Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Analytica Chimica Acta (v.585, #1)
Microfluidic chip accomplishing self-fluid replacement using only capillary force and its bioanalytical application by Kwang Hyo Chung; Jung Woo Hong; Dae-Sik Lee; Hyun C. Yoon (pp. 1-10).
A polymer microfluidic chip accomplishing automated sample flow and replacement without external controls and an application of the chip for bioanalytical reaction were described. All the fluidic operations in the chip were achieved by only natural capillary flow in a time-planned sequence. For the control of the capillary flow, the geometry of the channels and chambers in the chip was designed based on theoretical considerations and numerical simulations. The microfluidic chip was made by using polymer replication techniques, which were suitable for fast and cheap fabrication. The test for a biochemical analysis, employing an enzyme (HRP)-catalyzed precipitation reaction, exhibited a good performance using the developed chip. The presented microfluidic method would be applicable to biochemical lab-on-a-chips with integrated fluid replacement steps, such as affinity elution and solution exchange during biosensor signaling.
Keywords: Capillary force; Microfluidics; Polymer chip; Surface tension; Bioanalysis
Microfluidic chip accomplishing self-fluid replacement using only capillary force and its bioanalytical application by Kwang Hyo Chung; Jung Woo Hong; Dae-Sik Lee; Hyun C. Yoon (pp. 1-10).
A polymer microfluidic chip accomplishing automated sample flow and replacement without external controls and an application of the chip for bioanalytical reaction were described. All the fluidic operations in the chip were achieved by only natural capillary flow in a time-planned sequence. For the control of the capillary flow, the geometry of the channels and chambers in the chip was designed based on theoretical considerations and numerical simulations. The microfluidic chip was made by using polymer replication techniques, which were suitable for fast and cheap fabrication. The test for a biochemical analysis, employing an enzyme (HRP)-catalyzed precipitation reaction, exhibited a good performance using the developed chip. The presented microfluidic method would be applicable to biochemical lab-on-a-chips with integrated fluid replacement steps, such as affinity elution and solution exchange during biosensor signaling.
Keywords: Capillary force; Microfluidics; Polymer chip; Surface tension; Bioanalysis
Simultaneous microchip enzymatic measurements of blood lactate and glucose by Joseph Wang; Madhu Prakash Chatrathi; Greg E. Collins (pp. 11-16).
A miniaturized capillary electrophoretic (CE) microchip device for the simultaneous measurements of lactate and glucose is described. The new microchip bioassay protocol integrates an electrophoretic separation of lactate and glucose, post-column enzymatic reactions of these metabolites with their respective oxidase enzymes, and an amperometric (anodic) detection of enzymatically-liberated hydrogen peroxide at a gold-coated thick-film carbon detector. Factors influencing the response have been examined and optimized, and the analytical performance has been characterized. Applicability of the microchip assay to clinical samples, such as serum and blood, is demonstrated. The microchip protocol obviates cross enzymatic reactions and interferences from major oxidizable constituents common to dual glucose-lactate enzyme electrodes. Such ability to rapidly separate and quantitate lactate and glucose on a small microchip platform should find important clinical and biotechnological applications.
Keywords: Lactate; Glucose; Microchip; Electrochemical detection
Simultaneous microchip enzymatic measurements of blood lactate and glucose by Joseph Wang; Madhu Prakash Chatrathi; Greg E. Collins (pp. 11-16).
A miniaturized capillary electrophoretic (CE) microchip device for the simultaneous measurements of lactate and glucose is described. The new microchip bioassay protocol integrates an electrophoretic separation of lactate and glucose, post-column enzymatic reactions of these metabolites with their respective oxidase enzymes, and an amperometric (anodic) detection of enzymatically-liberated hydrogen peroxide at a gold-coated thick-film carbon detector. Factors influencing the response have been examined and optimized, and the analytical performance has been characterized. Applicability of the microchip assay to clinical samples, such as serum and blood, is demonstrated. The microchip protocol obviates cross enzymatic reactions and interferences from major oxidizable constituents common to dual glucose-lactate enzyme electrodes. Such ability to rapidly separate and quantitate lactate and glucose on a small microchip platform should find important clinical and biotechnological applications.
Keywords: Lactate; Glucose; Microchip; Electrochemical detection
Europium(III)-chelates embedded in nanoparticles are protected from interfering compounds present in assay media by Leena Kokko; Timo Lövgren; Tero Soukka (pp. 17-23).
Lanthanide chelates are excellent labels in ligand binding assays due to their long lifetime fluorescence, which enables efficient background reduction using time-resolved measurement. In separation-free homogeneous assays, however, some compounds in the sample may cause quenching of the lanthanide fluorescence and extra steps are required before these samples can be measured. In this study we have evaluated whether europium chelates packed inside a polystyrene nanoparticle are better protected from the environment than individual Eu(III)-chelates, and do these particles have higher tolerance against known interfering compounds (bivalent metal ions and variation of pH). We also tested whether metal ions had any effect on a fluorescence resonance energy transfer (FRET) based detection of a bioaffinity binding reaction. The presence of metal ions or variation of pH did not affect the fluorescence of the Eu(III)-chelate dyed nanoparticles, while significant decrease of the fluorescence was detected with a 9-dentate Eu(III)-chelate. Metal ions also decreased the fluorescence lifetime of the 9-dentate Eu(III)-chelate from 0.960 to 0.050ms. Coloured metal ions caused a minor decrease in sensitised emission generated by FRET when Eu(III)-chelate dyed nanoparticles were used as donor labels. The decreased signal was due to the absorption of the sensitised emission by the coloured metal ions, since the metal ions had no effect on the lifetime of the sensitised emission. Thus the Eu(III)-chelate dyed nanoparticles are preferred labels in homogeneous bioaffinity assays, when interfering compounds are known to be present.
Keywords: Europium; Nanoparticle; Time-resolved fluorescence; Homogeneous; Interfering compound
Europium(III)-chelates embedded in nanoparticles are protected from interfering compounds present in assay media by Leena Kokko; Timo Lövgren; Tero Soukka (pp. 17-23).
Lanthanide chelates are excellent labels in ligand binding assays due to their long lifetime fluorescence, which enables efficient background reduction using time-resolved measurement. In separation-free homogeneous assays, however, some compounds in the sample may cause quenching of the lanthanide fluorescence and extra steps are required before these samples can be measured. In this study we have evaluated whether europium chelates packed inside a polystyrene nanoparticle are better protected from the environment than individual Eu(III)-chelates, and do these particles have higher tolerance against known interfering compounds (bivalent metal ions and variation of pH). We also tested whether metal ions had any effect on a fluorescence resonance energy transfer (FRET) based detection of a bioaffinity binding reaction. The presence of metal ions or variation of pH did not affect the fluorescence of the Eu(III)-chelate dyed nanoparticles, while significant decrease of the fluorescence was detected with a 9-dentate Eu(III)-chelate. Metal ions also decreased the fluorescence lifetime of the 9-dentate Eu(III)-chelate from 0.960 to 0.050ms. Coloured metal ions caused a minor decrease in sensitised emission generated by FRET when Eu(III)-chelate dyed nanoparticles were used as donor labels. The decreased signal was due to the absorption of the sensitised emission by the coloured metal ions, since the metal ions had no effect on the lifetime of the sensitised emission. Thus the Eu(III)-chelate dyed nanoparticles are preferred labels in homogeneous bioaffinity assays, when interfering compounds are known to be present.
Keywords: Europium; Nanoparticle; Time-resolved fluorescence; Homogeneous; Interfering compound
A systematic study on the extractability of arsenic species from algal certified reference material IAEA-140/TM ( Fucus sp., Sea Plant Homogenate) using methanol/water extractant mixtures by Johannes Teun van Elteren; Zdenka Šlejkovec; Markus Kahn; Walter Goessler (pp. 24-31).
Using methanol/water mixtures (from pure water to pure methanol), with different desorption and solubility parameters, and varying extractant volume to algal mass ( V/ m) ratios, the extractability of arsenic species from CRM IAEA-140/TM was investigated. A linear sorption isotherm-based model was developed to process the data obtained with variable volume extraction, allowing the unambiguous deduction of the maximal extractable species concentrations under the specific extraction conditions, even for more stable species.The maximal extractable arsenic fraction ranged from 41 to 68% of the total arsenic concentration in CRM IAEA-140/TM, depending on the extractant composition, with pure methanol giving the lowest extraction yield and pure water giving erratic extractability (probably due to bad wettability). The main arsenic species quantified in the methanol/water extracts were arsenosugars, with arsenosugars 1 (glycerol arsenosugar), 3 (sulfonate arsenosugar) and 4 (sulfate arsenosugar) making up ca. 90% of the maximal extractable arsenic. The rest accounts for DMA (dimethylarsinate), arsenosugar 2 (phosphate arsenosugar) and As(V). There is no clear extraction pattern emerging from the data although it may be seen that extraction of more polar species (e.g. arsenosugar 1) is favoured in pure methanol and less polar more ionic species (e.g. arsenosugar 2 and As(V)) in methanol extractants with a higher water percentage.The precise and highly accurate data may be used for quality control purposes under strictly followed extraction conditions since the extraction is operationally defined. Additionally, the variable volume extraction methodology presented may be applied to other elemental species in other matrices using other extractants. Although this approach does not maximise the absolute extractability but only that which is extractant-specific, experimentators are forewarned that in most cases only a fingerprint of the extractant-specific species is produced unless a quantitative extraction of all species is obtained.
Keywords: Desorption; Solubility; Speciation; Algae; High performance liquid chromatography; Inductively coupled plasma mass spectrometry
A systematic study on the extractability of arsenic species from algal certified reference material IAEA-140/TM ( Fucus sp., Sea Plant Homogenate) using methanol/water extractant mixtures by Johannes Teun van Elteren; Zdenka Šlejkovec; Markus Kahn; Walter Goessler (pp. 24-31).
Using methanol/water mixtures (from pure water to pure methanol), with different desorption and solubility parameters, and varying extractant volume to algal mass ( V/ m) ratios, the extractability of arsenic species from CRM IAEA-140/TM was investigated. A linear sorption isotherm-based model was developed to process the data obtained with variable volume extraction, allowing the unambiguous deduction of the maximal extractable species concentrations under the specific extraction conditions, even for more stable species.The maximal extractable arsenic fraction ranged from 41 to 68% of the total arsenic concentration in CRM IAEA-140/TM, depending on the extractant composition, with pure methanol giving the lowest extraction yield and pure water giving erratic extractability (probably due to bad wettability). The main arsenic species quantified in the methanol/water extracts were arsenosugars, with arsenosugars 1 (glycerol arsenosugar), 3 (sulfonate arsenosugar) and 4 (sulfate arsenosugar) making up ca. 90% of the maximal extractable arsenic. The rest accounts for DMA (dimethylarsinate), arsenosugar 2 (phosphate arsenosugar) and As(V). There is no clear extraction pattern emerging from the data although it may be seen that extraction of more polar species (e.g. arsenosugar 1) is favoured in pure methanol and less polar more ionic species (e.g. arsenosugar 2 and As(V)) in methanol extractants with a higher water percentage.The precise and highly accurate data may be used for quality control purposes under strictly followed extraction conditions since the extraction is operationally defined. Additionally, the variable volume extraction methodology presented may be applied to other elemental species in other matrices using other extractants. Although this approach does not maximise the absolute extractability but only that which is extractant-specific, experimentators are forewarned that in most cases only a fingerprint of the extractant-specific species is produced unless a quantitative extraction of all species is obtained.
Keywords: Desorption; Solubility; Speciation; Algae; High performance liquid chromatography; Inductively coupled plasma mass spectrometry
Confirmation of vanadium complex formation using electrospray mass spectrometry and determination of vanadium speciation by sample stacking capillary electrophoresis by ZuLiang Chen; Gary Owens; Ravendra Naidu (pp. 32-37).
Capillary zone electrophoresis (CZE) with UV detection was used to determine vanadium species. Nitrilotriacetic acid (NTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), ethylene glycol-bis(2-aminoethylether)-tetraacetic acid (EGTA) and 2,6-pyridinedicarboxylic acid (PDCA) were investigated to determine whether these ligands formed stable anionic complexes with vanadium. Of all the ligands studied HEDTA was the most suitable ligand because it gave the largest UV response with reasonable migration time. Electrospray mass spectrometry (ES-MS) was used to confirm the formation of [VO2(HEDTA)]2− and [VO(HEDTA)]1− in solution. An electrolyte containing 25mM phosphate, 0.25mM tetradecyltrimethylammonium bromide (TTAB) at pH 5.5 was optimum for the separation of these anionic vanadium complexes. Sample stacking techniques, including large-volume sample stacking (LVSS) and field-amplified sample injection (FASI), were tested to improve the sensitivity. Best sensitivity was obtained using FASI, with detection limits of 0.001μM, equivalent to 0.4μgL−1, for [VO2(HEDTA)]2− and 0.01μM, equivalent to 3.4μgL−1 for [VO(HEDTA)]1−. The utility of the method for the speciation of V(IV) and V(V) was demonstrated using ground water samples.
Keywords: Capillary zone electrophoresis; Vanadium speciation; Electrospray mass spectrometry; Sample stacking techniques
Confirmation of vanadium complex formation using electrospray mass spectrometry and determination of vanadium speciation by sample stacking capillary electrophoresis by ZuLiang Chen; Gary Owens; Ravendra Naidu (pp. 32-37).
Capillary zone electrophoresis (CZE) with UV detection was used to determine vanadium species. Nitrilotriacetic acid (NTA), hydroxyethylethylenediaminetriacetic acid (HEDTA), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), ethylene glycol-bis(2-aminoethylether)-tetraacetic acid (EGTA) and 2,6-pyridinedicarboxylic acid (PDCA) were investigated to determine whether these ligands formed stable anionic complexes with vanadium. Of all the ligands studied HEDTA was the most suitable ligand because it gave the largest UV response with reasonable migration time. Electrospray mass spectrometry (ES-MS) was used to confirm the formation of [VO2(HEDTA)]2− and [VO(HEDTA)]1− in solution. An electrolyte containing 25mM phosphate, 0.25mM tetradecyltrimethylammonium bromide (TTAB) at pH 5.5 was optimum for the separation of these anionic vanadium complexes. Sample stacking techniques, including large-volume sample stacking (LVSS) and field-amplified sample injection (FASI), were tested to improve the sensitivity. Best sensitivity was obtained using FASI, with detection limits of 0.001μM, equivalent to 0.4μgL−1, for [VO2(HEDTA)]2− and 0.01μM, equivalent to 3.4μgL−1 for [VO(HEDTA)]1−. The utility of the method for the speciation of V(IV) and V(V) was demonstrated using ground water samples.
Keywords: Capillary zone electrophoresis; Vanadium speciation; Electrospray mass spectrometry; Sample stacking techniques
Aerosol time-of-flight mass spectrometry data analysis: A benchmark of clustering algorithms by Thomas P. Rebotier; Kimberly A. Prather (pp. 38-54).
Airborne particulate matter is an important component of atmospheric pollution, affecting human health, climate, and visibility. Modern instruments allow single particles to be analyzed one-by-one in real time, and offer the promise of determining the sources of individual particles based on their mass spectral signatures. The large number of particles to be apportioned makes clustering a necessary step. The goal of this study is to compare using mass spectral data the accuracy and speed of several clustering algorithms: ART-2a, several variants of hierarchical clustering, and K-means. Repeated simulations with various algorithms and different levels of data preprocessing suggest that hierarchical clustering methods using derivatives of Ward's algorithm discriminate sources with fewer errors than ART-2a, which itself discriminates much better than point-wise hierarchical clustering methods. In most cases, K-means algorithms do almost as well as the best hierarchical clustering. These efficient algorithms (clustering derived from Ward's algorithm, ART-2a and K-means) are most accurate when the relative peak areas have been pre-scaled by taking the square root. Analysis times vary within a factor of 30, and when accuracy above 95% is required, run times scale up as the square of the number of particles. Algorithms derived from Ward's remain the most accurate under a wide range of conditions and conversely, for an equal accuracy, can deliver a shorter list of clusters, allowing faster and maybe on-the-fly classification.
Keywords: Aerosol time-of-flight mass spectrometry (ATOFMS); Aerosol mass spectroscopy; Clustering; Data analysis; Hierarchical clustering; K; -means; ART-2a; Clustering accuracy; Runtimes; Spectral data preprocessing
Aerosol time-of-flight mass spectrometry data analysis: A benchmark of clustering algorithms by Thomas P. Rebotier; Kimberly A. Prather (pp. 38-54).
Airborne particulate matter is an important component of atmospheric pollution, affecting human health, climate, and visibility. Modern instruments allow single particles to be analyzed one-by-one in real time, and offer the promise of determining the sources of individual particles based on their mass spectral signatures. The large number of particles to be apportioned makes clustering a necessary step. The goal of this study is to compare using mass spectral data the accuracy and speed of several clustering algorithms: ART-2a, several variants of hierarchical clustering, and K-means. Repeated simulations with various algorithms and different levels of data preprocessing suggest that hierarchical clustering methods using derivatives of Ward's algorithm discriminate sources with fewer errors than ART-2a, which itself discriminates much better than point-wise hierarchical clustering methods. In most cases, K-means algorithms do almost as well as the best hierarchical clustering. These efficient algorithms (clustering derived from Ward's algorithm, ART-2a and K-means) are most accurate when the relative peak areas have been pre-scaled by taking the square root. Analysis times vary within a factor of 30, and when accuracy above 95% is required, run times scale up as the square of the number of particles. Algorithms derived from Ward's remain the most accurate under a wide range of conditions and conversely, for an equal accuracy, can deliver a shorter list of clusters, allowing faster and maybe on-the-fly classification.
Keywords: Aerosol time-of-flight mass spectrometry (ATOFMS); Aerosol mass spectroscopy; Clustering; Data analysis; Hierarchical clustering; K; -means; ART-2a; Clustering accuracy; Runtimes; Spectral data preprocessing
A Duffing oscillator algorithm to detect the weak chromatographic signal by Wei Zhang; Bing-Ren Xiang (pp. 55-59).
Based on the Duffing equation, a Duffing oscillator algorithm (DOA) to improve the signal-to-noise ratio (SNR) was presented. By simulated and experimental data sets, it was proven that the signal-to-noise ratio (SNR) of the weak signal could be greatly enhanced by this method. Using signal enhancement by DOA, this method extends the SNR of low concentrations of methylbenzene from 2.662 to 29.90 and the method can be used for quantitative analysis of methylbenzene, which are lower than detection limit of an analytical system. The Duffing oscillator algorithm (DOA) might be a promising tool to extend instrumental linear range and to improve the accuracy of trace analysis. The research enlarged the application scope of Duffing equation to chromatographic signal processing.
Keywords: Duffing equation; Signal-to-noise ratio; Weak signal; Liquid chromatography
A Duffing oscillator algorithm to detect the weak chromatographic signal by Wei Zhang; Bing-Ren Xiang (pp. 55-59).
Based on the Duffing equation, a Duffing oscillator algorithm (DOA) to improve the signal-to-noise ratio (SNR) was presented. By simulated and experimental data sets, it was proven that the signal-to-noise ratio (SNR) of the weak signal could be greatly enhanced by this method. Using signal enhancement by DOA, this method extends the SNR of low concentrations of methylbenzene from 2.662 to 29.90 and the method can be used for quantitative analysis of methylbenzene, which are lower than detection limit of an analytical system. The Duffing oscillator algorithm (DOA) might be a promising tool to extend instrumental linear range and to improve the accuracy of trace analysis. The research enlarged the application scope of Duffing equation to chromatographic signal processing.
Keywords: Duffing equation; Signal-to-noise ratio; Weak signal; Liquid chromatography
Improved stochastic resonance algorithm for enhancement of signal-to-noise ratio of high-performance liquid chromatographic signal by Shaofei Xie; Bingren Xiang; Haishan Deng; Suyun Xiang; Jun Lu (pp. 60-65).
Based on the theory of stochastic resonance, an improved stochastic resonance algorithm with a new criterion for optimizing system parameters to enhance signal-to-noise ratio (SNR) of HPLC/UV chromatographic signal for trace analysis was presented in this study. Compared with the conventional criterion in stochastic resonance, the proposed one can ensure satisfactory SNR as well as good peak shape of chromatographic peak in output signal. Application of the criterion to experimental weak signals of HPLC/UV was investigated and the results showed an excellent quantitative relationship between different concentrations and responses.
Keywords: Improved stochastic resonance; Signal-to-noise ratio; Chromatographic signal; High-performance liquid chromatography
Improved stochastic resonance algorithm for enhancement of signal-to-noise ratio of high-performance liquid chromatographic signal by Shaofei Xie; Bingren Xiang; Haishan Deng; Suyun Xiang; Jun Lu (pp. 60-65).
Based on the theory of stochastic resonance, an improved stochastic resonance algorithm with a new criterion for optimizing system parameters to enhance signal-to-noise ratio (SNR) of HPLC/UV chromatographic signal for trace analysis was presented in this study. Compared with the conventional criterion in stochastic resonance, the proposed one can ensure satisfactory SNR as well as good peak shape of chromatographic peak in output signal. Application of the criterion to experimental weak signals of HPLC/UV was investigated and the results showed an excellent quantitative relationship between different concentrations and responses.
Keywords: Improved stochastic resonance; Signal-to-noise ratio; Chromatographic signal; High-performance liquid chromatography
Neuro-genetic multioptimization of the determination of polychlorinated biphenyl congeners in human milk by headspace solid phase microextraction coupled to gas chromatography with electron capture detection by Cláudia Hoffmann Kowalski; Gilmare Antônia da Silva; Ronei Jesus Poppi; Helena Teixeira Godoy; Fabio Augusto (pp. 66-75).
Polychlorinated biphenyls (PCB) can eventually contaminate breast milk, which is a serious issue to the newborn due to their high vulnerability. Solid phase microextraction (SPME) can be a very convenient technique for their isolation and pre-concentration prior chromatographic analysis. Here, a simultaneous multioptimization strategy based on a neuro-genetic approach was applied to a headspace SPME method for determination of 12 PCB in human milk. Gas chromatography with electron capture detection (ECD) was adopted for the separation and detection of the analytes. Experiments according to a Doehlert design were carried out with varied extraction time and temperature, media ionic strength and concentration of the methanol (co-solvent). To find the best model that simultaneously correlate all PCB peak areas and SPME extraction conditions, a multivariate calibration method based on a Bayesian Neural Network (BNN) was applied. The net output from the neural network was used as input in a genetic algorithm (GA) optimization operation (neuro-genetic approach). The GA pointed out that the best values of the overall SPME operational conditions were the saturation of the media with NaCl, extraction temperature of 95°C, extraction time of 60min and addition of 5% (v/v) methanol to the media. These optimized parameters resulted in the decrease of the detection limits and increase on the sensitivity for all tested analytes, showing that the use of neuro-genetic approach can be a promising way for optimization of SPME methods.
Keywords: Multioptimization; Neuro-genetic approach; Doehlert design; Solid phase microextraction; Polychlorinated biphenyls
Neuro-genetic multioptimization of the determination of polychlorinated biphenyl congeners in human milk by headspace solid phase microextraction coupled to gas chromatography with electron capture detection by Cláudia Hoffmann Kowalski; Gilmare Antônia da Silva; Ronei Jesus Poppi; Helena Teixeira Godoy; Fabio Augusto (pp. 66-75).
Polychlorinated biphenyls (PCB) can eventually contaminate breast milk, which is a serious issue to the newborn due to their high vulnerability. Solid phase microextraction (SPME) can be a very convenient technique for their isolation and pre-concentration prior chromatographic analysis. Here, a simultaneous multioptimization strategy based on a neuro-genetic approach was applied to a headspace SPME method for determination of 12 PCB in human milk. Gas chromatography with electron capture detection (ECD) was adopted for the separation and detection of the analytes. Experiments according to a Doehlert design were carried out with varied extraction time and temperature, media ionic strength and concentration of the methanol (co-solvent). To find the best model that simultaneously correlate all PCB peak areas and SPME extraction conditions, a multivariate calibration method based on a Bayesian Neural Network (BNN) was applied. The net output from the neural network was used as input in a genetic algorithm (GA) optimization operation (neuro-genetic approach). The GA pointed out that the best values of the overall SPME operational conditions were the saturation of the media with NaCl, extraction temperature of 95°C, extraction time of 60min and addition of 5% (v/v) methanol to the media. These optimized parameters resulted in the decrease of the detection limits and increase on the sensitivity for all tested analytes, showing that the use of neuro-genetic approach can be a promising way for optimization of SPME methods.
Keywords: Multioptimization; Neuro-genetic approach; Doehlert design; Solid phase microextraction; Polychlorinated biphenyls
Fast determination of paeonol in plasma by headspace solid-phase microextraction followed by gas chromatography–mass spectrometry by Ling Dong; Chunhui Deng; Jiyao Wang; Xizhong Shen (pp. 76-80).
Paeonol is the active component in the traditional Chinese medicines (TCMs), such as Cynanchum paniculatum, which has been used to treat many diseases, such as eczema. In this work, a simple, rapid and sensitive method was developed for the determination of paeonol in rabbit plasma, which was based on headspace solid-phase microextraction (HS-SPME) followed by gas chromatography–mass spectrometry (GC–MS). The extraction parameters of fiber coating, sample temperature, extraction time, stirring rate and ion strength were systemically optimized; the method linearity, detection limit and precision were also investigated. It was shown that the proposed method provided a good linearity (0.02–20μgmL−1, R2>0.990), low detection limit (2.0ngmL−1) and good precision (R.S.D. value less than 8%). Finally, GC/MS following HS-SPME was applied to fast determination of paeonol in rabbit plasma at different time point after oral demonstration of Cynanchum paniculatum essential oil. The experimental results suggest that the proposed method provided an alternative and novel approach to the pharmacokinetics study of paeonol in the TCMs.
Keywords: Paeonol; Solid-phase microextraction; Gas chromatography–mass spectrometry; Plasma; Traditional Chinese medicine; Cynanchum paniculatum
Fast determination of paeonol in plasma by headspace solid-phase microextraction followed by gas chromatography–mass spectrometry by Ling Dong; Chunhui Deng; Jiyao Wang; Xizhong Shen (pp. 76-80).
Paeonol is the active component in the traditional Chinese medicines (TCMs), such as Cynanchum paniculatum, which has been used to treat many diseases, such as eczema. In this work, a simple, rapid and sensitive method was developed for the determination of paeonol in rabbit plasma, which was based on headspace solid-phase microextraction (HS-SPME) followed by gas chromatography–mass spectrometry (GC–MS). The extraction parameters of fiber coating, sample temperature, extraction time, stirring rate and ion strength were systemically optimized; the method linearity, detection limit and precision were also investigated. It was shown that the proposed method provided a good linearity (0.02–20μgmL−1, R2>0.990), low detection limit (2.0ngmL−1) and good precision (R.S.D. value less than 8%). Finally, GC/MS following HS-SPME was applied to fast determination of paeonol in rabbit plasma at different time point after oral demonstration of Cynanchum paniculatum essential oil. The experimental results suggest that the proposed method provided an alternative and novel approach to the pharmacokinetics study of paeonol in the TCMs.
Keywords: Paeonol; Solid-phase microextraction; Gas chromatography–mass spectrometry; Plasma; Traditional Chinese medicine; Cynanchum paniculatum
Per- O-methylation of neutral carbohydrates directly from aqueous samples for gas chromatography and mass spectrometry analysis by Ionel Ciucanu; Rodica Caprita (pp. 81-85).
Per- O-methylation of neutral carbohydrates in one step by adding dimethyl sulfoxide, powdered sodium hydroxide, and methyl iodide directly to aqueous sample is described. The influence of the water on the methylation reaction is investigated. Solid powdered sodium hydroxide is very hygroscopic and can scavenge the water from sample if an additional excess of sodium hydroxide is added. The degree of per- O-methylation of carbohydrates is checked by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Gas chromatography–mass spectrometry analysis of mono- and disaccharides from grape juice is presented.
Keywords: Per-; O; -methylation; Carbohydrates; Oligosaccharides; Gas chromatography; Mass spectrometry
Per- O-methylation of neutral carbohydrates directly from aqueous samples for gas chromatography and mass spectrometry analysis by Ionel Ciucanu; Rodica Caprita (pp. 81-85).
Per- O-methylation of neutral carbohydrates in one step by adding dimethyl sulfoxide, powdered sodium hydroxide, and methyl iodide directly to aqueous sample is described. The influence of the water on the methylation reaction is investigated. Solid powdered sodium hydroxide is very hygroscopic and can scavenge the water from sample if an additional excess of sodium hydroxide is added. The degree of per- O-methylation of carbohydrates is checked by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Gas chromatography–mass spectrometry analysis of mono- and disaccharides from grape juice is presented.
Keywords: Per-; O; -methylation; Carbohydrates; Oligosaccharides; Gas chromatography; Mass spectrometry
Oxidative status of human low density lipoprotein isolated by anion-exchange high-performance liquid chromatography—Assessment by total hydroxyoctadecadienoic acid, 7-hydroxycholesterol, and 8-iso-prostaglandin F2α by Soichi Kitano; Yasukazu Yoshida; Katsumi Kawano; Nozomu Hibi; Etsuo Niki (pp. 86-93).
This study aims to measure the oxidative status of LDL from human plasma ( n=26) as assessed by biomarkers for lipid peroxidation, total hydroxyoctadecadienoic acid (tHODE), 7α- and 7β-hydroxycholesterol (t7-OHCh), and 8-iso-prostaglandin F2α (t8-iso-PGF2α) after subfractionation of LDL with an anion-exchange HPLC (AE-HPLC). LDL was separated and quantified by AE-HPLC as LDL-1, LDL-2, and LDL-3 in the order of the anionic charge of the LDL particles. The concentrations of tHODE, t7-OHCh, and t8-iso-PGF2α in both plasma and LDL subfractions were assessed after reduction and saponification. In this method, the free and ester forms of hydroperoxides, ketones, and hydroxides of linoleic acid and cholesterol are measured as tHODE and t7-OHCh, respectively. It was found that tHODE significantly correlated with the proportion of LDL-2 and LDL-3 as well as with the concentration of malondialdehyde-modified LDL in plasma. Further, by the analyses of LDL subfractions, the concentrations of tHODE, t8-iso-PGF2α, and t7-OHCh in LDL-3 were found to be significantly higher than those in LDL-1 and LDL-2. These results clearly indicate that the extent of oxidation increases in the order of LDL-12α.
Keywords: Abbreviations; AE-HPLC; anion-exchange high-performance liquid chromatography; BSTFA; N,O-bis(trimethylsilyl)trifluoroacetamide; GOT; glutamic oxaloacetic transaminase; GPT; glutamic pyruvic transaminase; γ-GTP; γ-glutamyl transpeptidase; HDL; high density lipoprotein; 13-(; Z; ,; E; )-HODE; 13-hydroxy-9(; Z; ),11(E)-octadecadienoic acid; 13-(; E; ,; E; )-HODE; 13-hydroxy-9(; E; ),11(E)-octadecadienoic acid; 9-(; E; ,; Z; )-HODE; 9-hydroxy-10(; E; ),12(Z)-octadecadienoic; 9-(; E; ,; E; )-HODE; 9-hydroxy-10(; E; ),12(E)-octadecadienoic acid; 9-HODE-d; 4; 9S-hydroxy-10; E; ,12Z-octadecadienoic-9,10,12,13-d; 4; acid; HPODE; hydroperoxyoctadecadienoic acid; t8-iso-PGF; 2α; total 8-iso-prostaglandin F; 2α; 8-iso-PGF; 2α; -d; 4; 8-iso-prostaglandin F; 2α; -d; 4; LDL; low density lipoprotein; Lp(a); lipoprotein (a); PBS; phosphate-buffered saline; oxLDL; oxidized LDL; t20:4; total arachidonate; tCh; total cholesterol; t18:2; total linoleate; t7-OHCh; total 7-hydroxycholesterol; TG; triglyceride; tHODE; total hydroxyoctadecadienoic acid; MDA-LDL; malondialdehyde-modified LDL; PUFA; polyunsaturated fatty acid; αT; α-tocopherol; ZE; /; EE; stereoisomer ratio of HODE (9- and 13-(; Z; ,; E; )-HODE/9- and 13-(; E; ,; E; )-HODE)Low density lipoprotein; Lipid peroxidation; Total hydroxyoctadecadienoic acid; Total 7-hydroxycholesterol; Total 8-iso-prostaglandin F; 2α; Anion-exchange high-performance liquid chromatography
Oxidative status of human low density lipoprotein isolated by anion-exchange high-performance liquid chromatography—Assessment by total hydroxyoctadecadienoic acid, 7-hydroxycholesterol, and 8-iso-prostaglandin F2α by Soichi Kitano; Yasukazu Yoshida; Katsumi Kawano; Nozomu Hibi; Etsuo Niki (pp. 86-93).
This study aims to measure the oxidative status of LDL from human plasma ( n=26) as assessed by biomarkers for lipid peroxidation, total hydroxyoctadecadienoic acid (tHODE), 7α- and 7β-hydroxycholesterol (t7-OHCh), and 8-iso-prostaglandin F2α (t8-iso-PGF2α) after subfractionation of LDL with an anion-exchange HPLC (AE-HPLC). LDL was separated and quantified by AE-HPLC as LDL-1, LDL-2, and LDL-3 in the order of the anionic charge of the LDL particles. The concentrations of tHODE, t7-OHCh, and t8-iso-PGF2α in both plasma and LDL subfractions were assessed after reduction and saponification. In this method, the free and ester forms of hydroperoxides, ketones, and hydroxides of linoleic acid and cholesterol are measured as tHODE and t7-OHCh, respectively. It was found that tHODE significantly correlated with the proportion of LDL-2 and LDL-3 as well as with the concentration of malondialdehyde-modified LDL in plasma. Further, by the analyses of LDL subfractions, the concentrations of tHODE, t8-iso-PGF2α, and t7-OHCh in LDL-3 were found to be significantly higher than those in LDL-1 and LDL-2. These results clearly indicate that the extent of oxidation increases in the order of LDL-12α.
Keywords: Abbreviations; AE-HPLC; anion-exchange high-performance liquid chromatography; BSTFA; N,O-bis(trimethylsilyl)trifluoroacetamide; GOT; glutamic oxaloacetic transaminase; GPT; glutamic pyruvic transaminase; γ-GTP; γ-glutamyl transpeptidase; HDL; high density lipoprotein; 13-(; Z; ,; E; )-HODE; 13-hydroxy-9(; Z; ),11(E)-octadecadienoic acid; 13-(; E; ,; E; )-HODE; 13-hydroxy-9(; E; ),11(E)-octadecadienoic acid; 9-(; E; ,; Z; )-HODE; 9-hydroxy-10(; E; ),12(Z)-octadecadienoic; 9-(; E; ,; E; )-HODE; 9-hydroxy-10(; E; ),12(E)-octadecadienoic acid; 9-HODE-d; 4; 9S-hydroxy-10; E; ,12Z-octadecadienoic-9,10,12,13-d; 4; acid; HPODE; hydroperoxyoctadecadienoic acid; t8-iso-PGF; 2α; total 8-iso-prostaglandin F; 2α; 8-iso-PGF; 2α; -d; 4; 8-iso-prostaglandin F; 2α; -d; 4; LDL; low density lipoprotein; Lp(a); lipoprotein (a); PBS; phosphate-buffered saline; oxLDL; oxidized LDL; t20:4; total arachidonate; tCh; total cholesterol; t18:2; total linoleate; t7-OHCh; total 7-hydroxycholesterol; TG; triglyceride; tHODE; total hydroxyoctadecadienoic acid; MDA-LDL; malondialdehyde-modified LDL; PUFA; polyunsaturated fatty acid; αT; α-tocopherol; ZE; /; EE; stereoisomer ratio of HODE (9- and 13-(; Z; ,; E; )-HODE/9- and 13-(; E; ,; E; )-HODE)Low density lipoprotein; Lipid peroxidation; Total hydroxyoctadecadienoic acid; Total 7-hydroxycholesterol; Total 8-iso-prostaglandin F; 2α; Anion-exchange high-performance liquid chromatography
A general screening method for doping agents in human urine by solid phase extraction and liquid chromatography/time-of-flight mass spectrometry by Marjo Kolmonen; Antti Leinonen; Anna Pelander; Ilkka Ojanperä (pp. 94-102).
A general screening method based on solid phase extraction (SPE) and liquid chromatography/time-of-flight mass spectrometry (LC/TOFMS) was developed and investigated with 124 different doping agents, including stimulants,β-blockers, narcotics,β2-adrenergic agonists, agents with anti-estrogenic activity, diuretics and cannabinoids. Mixed mode cation exchange/C8 cartridges were applied to SPE, and chromatography was based on gradient elution on a C18 column. Ionization of the analytes was achieved with electrospray ionization in the positive mode. Identification by LC/TOFMS was based on retention time, accurate mass and isotopic pattern. Validation of the method consisted of analysis of specificity, analytical recovery, limit of detection and repeatability. The minimum required performance limit (MRPL), established by World Anti-Doping Agency (WADA), was attained to 97 doping agents. The extraction recoveries varied between 33 and 98% and the median was 58%. Mass accuracy was always better than 5 ppm, corresponding to a maximum mass error of 0.7 mDa. The repeatability of the method for spiked urine samples, expressed as median of relative standard deviations (RSD%) at concentrations of MRPL and 10 times MRPL, were 14% and 9%, respectively. The suitability of the LC/TOFMS method for doping control was demonstrated with authentic urine samples.
Keywords: Solid phase extraction; Liquid chromatography; Electrospray ionization; Time-of-flight mass spectrometry; Doping analysis
A general screening method for doping agents in human urine by solid phase extraction and liquid chromatography/time-of-flight mass spectrometry by Marjo Kolmonen; Antti Leinonen; Anna Pelander; Ilkka Ojanperä (pp. 94-102).
A general screening method based on solid phase extraction (SPE) and liquid chromatography/time-of-flight mass spectrometry (LC/TOFMS) was developed and investigated with 124 different doping agents, including stimulants,β-blockers, narcotics,β2-adrenergic agonists, agents with anti-estrogenic activity, diuretics and cannabinoids. Mixed mode cation exchange/C8 cartridges were applied to SPE, and chromatography was based on gradient elution on a C18 column. Ionization of the analytes was achieved with electrospray ionization in the positive mode. Identification by LC/TOFMS was based on retention time, accurate mass and isotopic pattern. Validation of the method consisted of analysis of specificity, analytical recovery, limit of detection and repeatability. The minimum required performance limit (MRPL), established by World Anti-Doping Agency (WADA), was attained to 97 doping agents. The extraction recoveries varied between 33 and 98% and the median was 58%. Mass accuracy was always better than 5 ppm, corresponding to a maximum mass error of 0.7 mDa. The repeatability of the method for spiked urine samples, expressed as median of relative standard deviations (RSD%) at concentrations of MRPL and 10 times MRPL, were 14% and 9%, respectively. The suitability of the LC/TOFMS method for doping control was demonstrated with authentic urine samples.
Keywords: Solid phase extraction; Liquid chromatography; Electrospray ionization; Time-of-flight mass spectrometry; Doping analysis
High-performance liquid chromatography and pharmacokinetics of aceclofenac in rats by Prashant Musmade; G. Subramanian; K.K. Srinivasan (pp. 103-109).
A simple and sensitive high-performance liquid chromatographic (HPLC) method was developed for quantification of aceclofenac in rat plasma. Ibuprofen was used as an internal standard (IS). The present method used protein precipitation for extraction of aceclofenac from rat plasma. Separation was carried out on reversed-phase C18 column (250mm×4.6mm, 5μ) and the column effluent was monitored by UV detector at 282nm. The mobile phase used was methanol-triethylamine (pH 7.0; 0.3% v/v in Milli-Q water) (60:40%, v/v) at a flow rate of 1.0mLmin−1. This method was linear over the range of 50.0–3500.0ngmL−1 with regression coefficient greater than 0.99. The mean recovery of aceclofenac and IS were 84.62±3.23 and 89.19±1.57%, respectively and the method was found to be precise, accurate, and specific during the study. The method was successfully applied for pharmacokinetic study of aceclofenac in rats.
Keywords: High-performance liquid chromatography; Aceclofenac; Pharmacokinetics
High-performance liquid chromatography and pharmacokinetics of aceclofenac in rats by Prashant Musmade; G. Subramanian; K.K. Srinivasan (pp. 103-109).
A simple and sensitive high-performance liquid chromatographic (HPLC) method was developed for quantification of aceclofenac in rat plasma. Ibuprofen was used as an internal standard (IS). The present method used protein precipitation for extraction of aceclofenac from rat plasma. Separation was carried out on reversed-phase C18 column (250mm×4.6mm, 5μ) and the column effluent was monitored by UV detector at 282nm. The mobile phase used was methanol-triethylamine (pH 7.0; 0.3% v/v in Milli-Q water) (60:40%, v/v) at a flow rate of 1.0mLmin−1. This method was linear over the range of 50.0–3500.0ngmL−1 with regression coefficient greater than 0.99. The mean recovery of aceclofenac and IS were 84.62±3.23 and 89.19±1.57%, respectively and the method was found to be precise, accurate, and specific during the study. The method was successfully applied for pharmacokinetic study of aceclofenac in rats.
Keywords: High-performance liquid chromatography; Aceclofenac; Pharmacokinetics
Identification and quantification of the main organic components of vinegars by high resolution1H NMR spectroscopy by A. Caligiani; D. Acquotti; G. Palla; V. Bocchi (pp. 110-119).
A detailed analysis of the proton high-field NMR spectra of vinegars (in particular of Italian balsamic vinegars) is reported. A large number of organic substances belonging to different classes, such as carbohydrates, alcohols, organic acids, volatile compounds and amino acids, were assigned. The possibility of quantification of the substances identified in the whole vinegar sample, without extraction or pre-concentration steps, was also tested. The data validity was demonstrated in terms of precision, accuracy, repeatability and inter-day reproducibility. The effects of the most critical experimental parameters (sample concentration, water suppression and relaxation time) on the analysis response were also discussed.1H NMR results were compared with those obtained by traditional techniques (GC–MS, titrations), and good correlations were obtained. The results showed that1H NMR with water suppression allows a rapid, simultaneous determination of carbohydrates (glucose and fructose), organic acids (acetic, formic, lactic, malic, citric, succinic and tartaric acids), alcohols and polyols (ethanol, acetoin, 2,3-butanediol, hydroxymethylfurfural), and volatile substances (ethyl acetate) in vinegar samples. On the contrary, the amino acid determination without sample pre-concentration was critical. The1H NMR method proposed was applied to different samples of vinegars, allowing, in particular, the discrimination of vinegars and balsamic vinegars.
Keywords: Quantitative analysis; 1; H NMR; Vinegars; Balsamic vinegars
Identification and quantification of the main organic components of vinegars by high resolution1H NMR spectroscopy by A. Caligiani; D. Acquotti; G. Palla; V. Bocchi (pp. 110-119).
A detailed analysis of the proton high-field NMR spectra of vinegars (in particular of Italian balsamic vinegars) is reported. A large number of organic substances belonging to different classes, such as carbohydrates, alcohols, organic acids, volatile compounds and amino acids, were assigned. The possibility of quantification of the substances identified in the whole vinegar sample, without extraction or pre-concentration steps, was also tested. The data validity was demonstrated in terms of precision, accuracy, repeatability and inter-day reproducibility. The effects of the most critical experimental parameters (sample concentration, water suppression and relaxation time) on the analysis response were also discussed.1H NMR results were compared with those obtained by traditional techniques (GC–MS, titrations), and good correlations were obtained. The results showed that1H NMR with water suppression allows a rapid, simultaneous determination of carbohydrates (glucose and fructose), organic acids (acetic, formic, lactic, malic, citric, succinic and tartaric acids), alcohols and polyols (ethanol, acetoin, 2,3-butanediol, hydroxymethylfurfural), and volatile substances (ethyl acetate) in vinegar samples. On the contrary, the amino acid determination without sample pre-concentration was critical. The1H NMR method proposed was applied to different samples of vinegars, allowing, in particular, the discrimination of vinegars and balsamic vinegars.
Keywords: Quantitative analysis; 1; H NMR; Vinegars; Balsamic vinegars
Homogeneous non-competitive bioaffinity assay based on fluorescence resonance energy transfer by Tiina Kokko; Leena Kokko; Tero Soukka; Timo Lövgren (pp. 120-125).
A homogeneous non-competitive assay principle for measurement of small analytes based on quenching of fluorescence is described. Fluorescence resonance energy transfer (FRET) occurs between the donor, intrinsically fluorescent europium(III)-chelate conjugated to streptavidin, and the acceptor, quencher dye conjugated to biotin derivative when the biotin–quencher is bound to Eu–streptavidin. Fluorescence can be measured only from those streptavidins that are bound to biotin of the sample, while the fluorescence of the streptavidins that are not occupied by biotin are quenched by quencher–biotin conjugates. The quenching efficiencies of the non-fluorescent quencher dyes were over 95% and one dye molecule was able to quench the fluorescence of more than one europium(III)-chelate. This, however, together with the quadrovalent nature of streptavidin limited the measurable range of the assay to 0.2–2nmolL−1. In this study we demonstrated that FRET could be used to design a non-competitive homogeneous assay for a small analyte resulting in equal performance with competitive heterogeneous assay.
Keywords: Fluorescence resonance energy transfer; Homogeneous; Non-competitive; Hapten
Homogeneous non-competitive bioaffinity assay based on fluorescence resonance energy transfer by Tiina Kokko; Leena Kokko; Tero Soukka; Timo Lövgren (pp. 120-125).
A homogeneous non-competitive assay principle for measurement of small analytes based on quenching of fluorescence is described. Fluorescence resonance energy transfer (FRET) occurs between the donor, intrinsically fluorescent europium(III)-chelate conjugated to streptavidin, and the acceptor, quencher dye conjugated to biotin derivative when the biotin–quencher is bound to Eu–streptavidin. Fluorescence can be measured only from those streptavidins that are bound to biotin of the sample, while the fluorescence of the streptavidins that are not occupied by biotin are quenched by quencher–biotin conjugates. The quenching efficiencies of the non-fluorescent quencher dyes were over 95% and one dye molecule was able to quench the fluorescence of more than one europium(III)-chelate. This, however, together with the quadrovalent nature of streptavidin limited the measurable range of the assay to 0.2–2nmolL−1. In this study we demonstrated that FRET could be used to design a non-competitive homogeneous assay for a small analyte resulting in equal performance with competitive heterogeneous assay.
Keywords: Fluorescence resonance energy transfer; Homogeneous; Non-competitive; Hapten
The derivatisation of avermectins and milbemycins in milk: New insights and improvement of the procedure by Bjorn J.A. Berendsen; Patrick P.J. Mulder; Hans (J.)A. van Rhijn (pp. 126-133).
Derivatisation of the avermectines ivermectin (IVM), doramectin (DOR), abamectin (ABA) and eprinomectin (EPR), and the milbemycin moxidectin (MOX) to fluorescent derivatives is commonly used for quantitative analysis at relevant levels using high performance liquid chromatography (HPLC) with fluorescence detection. Problems associated with the differences in reactivity towards derivatisation (EPM) and limited stability of the derived products (IVM, DOR, ABA) may seriously hamper the applicability of the method and the reliability of the obtained results. A study was performed to obtain more insight in this derivatisation process from an organic chemistry point of view. This study demonstrated the occurrence of two main fluorescent derivatives: the trifluoroacetyl esters (flu-TFA) and the derivatives with a free hydroxy group at the glycosidic ring (flu-OH). Optimisation of the derivatisation conditions resulted in a fast and reproducible formation of the fluorescent derivatives for all analytes including EPM. The improved procedure involves the addition of 1-methylimidazole (MI), trifluoroacetic anhydride (TFAA), triethylamine (TEA) and trifluoroacetic acid (TFA) with a subsequent incubation for 30min at 70°C. With this procedure for IVM, DOR and ABA flu-TFA derivatives are obtained instead of flu-OH derivatives as generally described in literature. The derivatisation is reproducible in different milk samples and the derivatives proved to be stable for at least 80h at room temperature. Using the optimised procedure a limit of detection (LoD) of 0.1μgkg−1 in milk was readily obtained.
Keywords: Avermectins; Milbemycins; Derivatisation; Fluorescence; Eprinomectin
The derivatisation of avermectins and milbemycins in milk: New insights and improvement of the procedure by Bjorn J.A. Berendsen; Patrick P.J. Mulder; Hans (J.)A. van Rhijn (pp. 126-133).
Derivatisation of the avermectines ivermectin (IVM), doramectin (DOR), abamectin (ABA) and eprinomectin (EPR), and the milbemycin moxidectin (MOX) to fluorescent derivatives is commonly used for quantitative analysis at relevant levels using high performance liquid chromatography (HPLC) with fluorescence detection. Problems associated with the differences in reactivity towards derivatisation (EPM) and limited stability of the derived products (IVM, DOR, ABA) may seriously hamper the applicability of the method and the reliability of the obtained results. A study was performed to obtain more insight in this derivatisation process from an organic chemistry point of view. This study demonstrated the occurrence of two main fluorescent derivatives: the trifluoroacetyl esters (flu-TFA) and the derivatives with a free hydroxy group at the glycosidic ring (flu-OH). Optimisation of the derivatisation conditions resulted in a fast and reproducible formation of the fluorescent derivatives for all analytes including EPM. The improved procedure involves the addition of 1-methylimidazole (MI), trifluoroacetic anhydride (TFAA), triethylamine (TEA) and trifluoroacetic acid (TFA) with a subsequent incubation for 30min at 70°C. With this procedure for IVM, DOR and ABA flu-TFA derivatives are obtained instead of flu-OH derivatives as generally described in literature. The derivatisation is reproducible in different milk samples and the derivatives proved to be stable for at least 80h at room temperature. Using the optimised procedure a limit of detection (LoD) of 0.1μgkg−1 in milk was readily obtained.
Keywords: Avermectins; Milbemycins; Derivatisation; Fluorescence; Eprinomectin
Simple and sensitive fluorimetric method for determination of environmental hormone bisphenol A based on its inhibitory effect on the redox reaction between peroxyl radical and rhodamine 6G by Jing Fan; Huiqin Guo; Guoguang Liu; Pingan Peng (pp. 134-138).
Peroxyl radical produced by Fenton-like reagent (Fe(III)+H2O2) oxidizes Rhodamine 6G and produces the quenching of its fluorescence. It is also found that bisphenol A has an inhibitory effect on the redox reaction. Based on this observation, an inhibitory kinetic fluorimetric method is reported for the determination of trace bisphenol A. The fluorescent inhibition of rhodamine 6G is measured by fix-time method. Under the optimum experimental conditions, the detection limit and the quantification limit for bisphenol A is 2.0 and 6.7ngmL−1, respectively; and the linear range of the determination is 0.024–0.4μgmL−1. The proposed method has been used for the determination of bisphenol A in environmental waters, river bottom sediment, generic soil, polycarbonate products and teeth filling samples with recoveries of 92.5–110.0%. The possible mechanism of the reaction has also been discussed.
Keywords: Fenton-like reagent; Peroxyl radical; Inhibitory fluorimetric method; Bisphenol A; Environmental samples
Simple and sensitive fluorimetric method for determination of environmental hormone bisphenol A based on its inhibitory effect on the redox reaction between peroxyl radical and rhodamine 6G by Jing Fan; Huiqin Guo; Guoguang Liu; Pingan Peng (pp. 134-138).
Peroxyl radical produced by Fenton-like reagent (Fe(III)+H2O2) oxidizes Rhodamine 6G and produces the quenching of its fluorescence. It is also found that bisphenol A has an inhibitory effect on the redox reaction. Based on this observation, an inhibitory kinetic fluorimetric method is reported for the determination of trace bisphenol A. The fluorescent inhibition of rhodamine 6G is measured by fix-time method. Under the optimum experimental conditions, the detection limit and the quantification limit for bisphenol A is 2.0 and 6.7ngmL−1, respectively; and the linear range of the determination is 0.024–0.4μgmL−1. The proposed method has been used for the determination of bisphenol A in environmental waters, river bottom sediment, generic soil, polycarbonate products and teeth filling samples with recoveries of 92.5–110.0%. The possible mechanism of the reaction has also been discussed.
Keywords: Fenton-like reagent; Peroxyl radical; Inhibitory fluorimetric method; Bisphenol A; Environmental samples
Analysis of close proximity quenching of phosphorescent metalloporphyrin labels in oligonucleotide structures by M. Burke; P.J. O'Sullivan; G.V. Ponomarev; D.V. Yashunsky; D.B. Papkovsky (pp. 139-146).
Quenching of phosphorescent platinum(II) and palladium(II) coproporphyrin (MeCP) labelled oligonucleotides was investigated. Strong hybridization-specific quenching was observed in duplex DNA structures with a variety of quenchers and with two identical porphyrin labels when in close proximity. Classical resonance energy transfer mechanism was ruled out, since quenching did not correlate with spectral overlaps and lifetime changes were insignificant. Quenching of MeCP by the free quenchers in solution revealed that porphyrin–porphyrin quenching is predominantly static while other dyes quench dynamically. The results suggest that the quenching in DNA duplex proceeds via direct contact.
Keywords: Oligonucleotide probes; Metalloporphyrin labels; Phosphorescence; Close proximity quenching; Hybridization assays
Analysis of close proximity quenching of phosphorescent metalloporphyrin labels in oligonucleotide structures by M. Burke; P.J. O'Sullivan; G.V. Ponomarev; D.V. Yashunsky; D.B. Papkovsky (pp. 139-146).
Quenching of phosphorescent platinum(II) and palladium(II) coproporphyrin (MeCP) labelled oligonucleotides was investigated. Strong hybridization-specific quenching was observed in duplex DNA structures with a variety of quenchers and with two identical porphyrin labels when in close proximity. Classical resonance energy transfer mechanism was ruled out, since quenching did not correlate with spectral overlaps and lifetime changes were insignificant. Quenching of MeCP by the free quenchers in solution revealed that porphyrin–porphyrin quenching is predominantly static while other dyes quench dynamically. The results suggest that the quenching in DNA duplex proceeds via direct contact.
Keywords: Oligonucleotide probes; Metalloporphyrin labels; Phosphorescence; Close proximity quenching; Hybridization assays
Chemiluminescence detection of organic peroxides in a two-phase system by Stefan Baj; Tomasz Krawczyk (pp. 147-153).
Potential application of chemiluminescence (CL) reaction of luminol for detection of organic peroxides by HPLC post-column reaction using an immiscible apolar eluent (hexane) with aqueous solution of luminol has been proposed. The positive influence of the addition of an anionic surface-active agent—sodium dodecyl sulphate (SDS) to the luminol solution on the CL intensity has been observed. The sensitivity of the method is greater for peroxyacid and hydroperoxide tested, and lesser for diacyl peroxide as compared to system with polar eluent miscible with solution of luminol. Our interpretation of observed results based on the extraction efficiency, CL kinetics and microemulsion formation has been suggested.
Keywords: Chromatography chemiluminescence; Luminol; Organic peroxides
Chemiluminescence detection of organic peroxides in a two-phase system by Stefan Baj; Tomasz Krawczyk (pp. 147-153).
Potential application of chemiluminescence (CL) reaction of luminol for detection of organic peroxides by HPLC post-column reaction using an immiscible apolar eluent (hexane) with aqueous solution of luminol has been proposed. The positive influence of the addition of an anionic surface-active agent—sodium dodecyl sulphate (SDS) to the luminol solution on the CL intensity has been observed. The sensitivity of the method is greater for peroxyacid and hydroperoxide tested, and lesser for diacyl peroxide as compared to system with polar eluent miscible with solution of luminol. Our interpretation of observed results based on the extraction efficiency, CL kinetics and microemulsion formation has been suggested.
Keywords: Chromatography chemiluminescence; Luminol; Organic peroxides
Potentiometric evaluation of calix[4]arene anion receptors in membrane electrodes: Phosphate detection by Francine Kivlehan; Wade J. Mace; Humphrey A. Moynihan; Damien W.M. Arrigan (pp. 154-160).
Ion-selective membrane electrodes doped with the urea- or thiourea-functionalised calix[4]arenes, 5,11,17,23-tetra- tert-butyl-25,27-bis[[4- N′-(phenylureido)butyl]oxy]-26,28-dipropoxy calix[4]arene (I) and 5,11,17,23-tetra- tert-butyl-25,27-bis[[4-( N′-phenylthioureido)-butyl]oxy]-26,28-dipropoxy calix[4]arene (II), were evaluated for anion sensing. Potentiometric results show that these calixarene ionophore-based membrane electrodes exhibit a good sensitivity to aqueous solutions of the monohydrogen orthophosphate species HPO42− in the concentration range 5.0×10−5 to 1.0×10−1M, with near-Nernstian response slopes of −33.0 and −28.0mVdec−1 for ionophoresI andII, respectively. Selectivity coefficient values for monohydrogen orthophosphate over a range of common anions were determined by the fixed interference and matched potential methods and indicated that these membrane electrodes exhibit a good selectivity for HPO42− with respect to the other anions, including sulfate and nitrate.
Keywords: Phosphate; Ion-selective electrode; Calixarene; Sensor; Selectivity
Potentiometric evaluation of calix[4]arene anion receptors in membrane electrodes: Phosphate detection by Francine Kivlehan; Wade J. Mace; Humphrey A. Moynihan; Damien W.M. Arrigan (pp. 154-160).
Ion-selective membrane electrodes doped with the urea- or thiourea-functionalised calix[4]arenes, 5,11,17,23-tetra- tert-butyl-25,27-bis[[4- N′-(phenylureido)butyl]oxy]-26,28-dipropoxy calix[4]arene (I) and 5,11,17,23-tetra- tert-butyl-25,27-bis[[4-( N′-phenylthioureido)-butyl]oxy]-26,28-dipropoxy calix[4]arene (II), were evaluated for anion sensing. Potentiometric results show that these calixarene ionophore-based membrane electrodes exhibit a good sensitivity to aqueous solutions of the monohydrogen orthophosphate species HPO42− in the concentration range 5.0×10−5 to 1.0×10−1M, with near-Nernstian response slopes of −33.0 and −28.0mVdec−1 for ionophoresI andII, respectively. Selectivity coefficient values for monohydrogen orthophosphate over a range of common anions were determined by the fixed interference and matched potential methods and indicated that these membrane electrodes exhibit a good selectivity for HPO42− with respect to the other anions, including sulfate and nitrate.
Keywords: Phosphate; Ion-selective electrode; Calixarene; Sensor; Selectivity
8-Hydroxyquinoline based neutral tripodal ionophore as a copper (II) selective electrode and the effect of remote substitutents on electrode properties by Susheel K. Mittal; Ashok Kumar S.K.; Nidhi Gupta; Sukhdeep Kaur; Subodh Kumar (pp. 161-170).
New PVC membrane ion selective electrodes based on 1,3,5-Tris(8-quinolinoxymethyl)-2,4,6-trimethylbenzene (MO8HQ) are reported. The basic sensing material belongs to the group of tripodal ionophores. Also their derivatives prepared by placing suitable substitutents at fifth position of 8-oxine moiety, i.e, 1,3,5-Tris(5-chloro-8-quinolinoxymethyl)-2,4,6-trimethylbenzene (5CHQ), 1,3,5-Tris(5-benzoyl-8-quinolinoxymethyl)-2,4,6-trimethylbenzene (5BHQ) and 1,3,5-Tris[(5-phenylhydroxymethylene)-8-quinolinoxymethyl]-2,4,6-trimethylbenzene (HYD-8HQ) ionophores have also been used to make copper-selective membrane electrodes. Among all the four electrodes, MO8HQ and HYD-8HQ ionophores based electrodes show excellent response towards Cu (II) ions. The electrodes having composition 33% PVC, 4% MO8HQ and 63% dibutyl phthalate (DBP) and 33% PVC, 6% HYD-8HQ, 63% dibutyl phthalate (DBP) exhibit a good Nernstian response to Cu (II) ions in the range of 1.0×10−6 to 1×10−1M. The electrode shows a reasonably fast response time of 15s. The effect of pH and electrode response is also reported. It shows good selectivity for Cu (II) ions in comparison to heavy metal ions, transition metal ions and for alkali and alkaline earth metal ions. The electrode response and selectivity remains unchanged for at least 5 months. The electrode can be used as an indicator electrode in the potentiometric titration of Cu (II) ions with EDTA.
Keywords: 8-Hydroxyquinoline; Tripodal; Copper (II); Selectivity co-efficients; Membrane electrode
8-Hydroxyquinoline based neutral tripodal ionophore as a copper (II) selective electrode and the effect of remote substitutents on electrode properties by Susheel K. Mittal; Ashok Kumar S.K.; Nidhi Gupta; Sukhdeep Kaur; Subodh Kumar (pp. 161-170).
New PVC membrane ion selective electrodes based on 1,3,5-Tris(8-quinolinoxymethyl)-2,4,6-trimethylbenzene (MO8HQ) are reported. The basic sensing material belongs to the group of tripodal ionophores. Also their derivatives prepared by placing suitable substitutents at fifth position of 8-oxine moiety, i.e, 1,3,5-Tris(5-chloro-8-quinolinoxymethyl)-2,4,6-trimethylbenzene (5CHQ), 1,3,5-Tris(5-benzoyl-8-quinolinoxymethyl)-2,4,6-trimethylbenzene (5BHQ) and 1,3,5-Tris[(5-phenylhydroxymethylene)-8-quinolinoxymethyl]-2,4,6-trimethylbenzene (HYD-8HQ) ionophores have also been used to make copper-selective membrane electrodes. Among all the four electrodes, MO8HQ and HYD-8HQ ionophores based electrodes show excellent response towards Cu (II) ions. The electrodes having composition 33% PVC, 4% MO8HQ and 63% dibutyl phthalate (DBP) and 33% PVC, 6% HYD-8HQ, 63% dibutyl phthalate (DBP) exhibit a good Nernstian response to Cu (II) ions in the range of 1.0×10−6 to 1×10−1M. The electrode shows a reasonably fast response time of 15s. The effect of pH and electrode response is also reported. It shows good selectivity for Cu (II) ions in comparison to heavy metal ions, transition metal ions and for alkali and alkaline earth metal ions. The electrode response and selectivity remains unchanged for at least 5 months. The electrode can be used as an indicator electrode in the potentiometric titration of Cu (II) ions with EDTA.
Keywords: 8-Hydroxyquinoline; Tripodal; Copper (II); Selectivity co-efficients; Membrane electrode
Chromium(III) selective membrane sensors based on Schiff bases as chelating ionophores by A.K. Singh; V.K. Gupta; Barkha Gupta (pp. 171-178).
The two chromium chelates of Schiff bases, N-(acetoacetanilide)-1,2-diaminoethane (L1) and N, N′-bis(acetoacetanilide)-triethylenetetraammine (L2), have been synthesized and explored as neutral ionophores for preparing poly(vinylchloride) (PVC) based membrane sensors selective to Cr(III). The addition of lipophilic anion excluder (NaTPB) and various plasticizers viz. o-Nitrophenyloctyl ether ( o-NPOE), dioctylpthalate (DOP), dibutylphthalate (DBP), tris(2-ethylhexyl)phosphate (TEHP), and benzyl acetate (BA) have found to improve the performance of the sensors. The best performance was obtained for the membrane sensor having a composition ofL1:PVC:DBP:NaTPB in the ratio 5:150:250:3 (w/w). The sensor exhibits Nernstian response in the concentration range 8.9×10−8 to 1.0×10−1M Cr3+ with limit of detection 5.6×10−8M. The proposed sensor manifest advantages of relatively fast response (10s) and good selectivity over some alkali, alkaline earth, transition and heavy metal ions. The selectivity behavior of the proposed electrode revealed a considerable improvement as compared to the best previously PVC-membrane electrode for chromium(III) ion. The potentiometric response of the proposed sensor was independent of pH of the test solution in the range of 2.0–7.0. The sensor has found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol and acetonitrile and could be used for a period of 3 months. The proposed electrode was used as an indicator electrode in potentiometric titration of chromium ion with EDTA and in direct determination in different water and food samples.
Keywords: Chromium selective electrode; Poly(vinylchloride) membranes; Schiff base and potentiometric sensors
Chromium(III) selective membrane sensors based on Schiff bases as chelating ionophores by A.K. Singh; V.K. Gupta; Barkha Gupta (pp. 171-178).
The two chromium chelates of Schiff bases, N-(acetoacetanilide)-1,2-diaminoethane (L1) and N, N′-bis(acetoacetanilide)-triethylenetetraammine (L2), have been synthesized and explored as neutral ionophores for preparing poly(vinylchloride) (PVC) based membrane sensors selective to Cr(III). The addition of lipophilic anion excluder (NaTPB) and various plasticizers viz. o-Nitrophenyloctyl ether ( o-NPOE), dioctylpthalate (DOP), dibutylphthalate (DBP), tris(2-ethylhexyl)phosphate (TEHP), and benzyl acetate (BA) have found to improve the performance of the sensors. The best performance was obtained for the membrane sensor having a composition ofL1:PVC:DBP:NaTPB in the ratio 5:150:250:3 (w/w). The sensor exhibits Nernstian response in the concentration range 8.9×10−8 to 1.0×10−1M Cr3+ with limit of detection 5.6×10−8M. The proposed sensor manifest advantages of relatively fast response (10s) and good selectivity over some alkali, alkaline earth, transition and heavy metal ions. The selectivity behavior of the proposed electrode revealed a considerable improvement as compared to the best previously PVC-membrane electrode for chromium(III) ion. The potentiometric response of the proposed sensor was independent of pH of the test solution in the range of 2.0–7.0. The sensor has found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol and acetonitrile and could be used for a period of 3 months. The proposed electrode was used as an indicator electrode in potentiometric titration of chromium ion with EDTA and in direct determination in different water and food samples.
Keywords: Chromium selective electrode; Poly(vinylchloride) membranes; Schiff base and potentiometric sensors
Net analyte signal-based simultaneous determination of ethanol and water by quartz crystal nanobalance sensor by A. Mirmohseni; H. Abdollahi; K. Rostamizadeh (pp. 179-184).
Net analyte signal (NAS)-based method called HLA/GO was applied for the selectively determination of binary mixture of ethanol and water by quartz crystal nanobalance (QCN) sensor. A full factorial design was applied for the formation of calibration and prediction sets in the concentration ranges 5.5–22.2μgmL−1 for ethanol and 7.01–28.07μgmL−1 for water. An optimal time range was selected by procedure which was based on the calculation of the net analyte signal regression plot in any considered time window for each test sample. A moving window strategy was used for searching the region with maximum linearity of NAS regression plot (minimum error indicator) and minimum of PRESS value. On the base of obtained results, the differences on the adsorption profiles in the time range between 1 and 600s were used to determine mixtures of both compounds by HLA/GO method. The calculation of the net analytical signal using HLA/GO method allows determination of several figures of merit like selectivity, sensitivity, analytical sensitivity and limit of detection, for each component. To check the ability of the proposed method in the selection of linear regions of adsorption profile, a test for detecting non-linear regions of adsorption profile data in the presence of methanol was also described. The results showed that the method was successfully applied for the determination of ethanol and water.
Keywords: Quartz crystal nanobalance (QCN); Net analyte signal-based method; Ethanol
Net analyte signal-based simultaneous determination of ethanol and water by quartz crystal nanobalance sensor by A. Mirmohseni; H. Abdollahi; K. Rostamizadeh (pp. 179-184).
Net analyte signal (NAS)-based method called HLA/GO was applied for the selectively determination of binary mixture of ethanol and water by quartz crystal nanobalance (QCN) sensor. A full factorial design was applied for the formation of calibration and prediction sets in the concentration ranges 5.5–22.2μgmL−1 for ethanol and 7.01–28.07μgmL−1 for water. An optimal time range was selected by procedure which was based on the calculation of the net analyte signal regression plot in any considered time window for each test sample. A moving window strategy was used for searching the region with maximum linearity of NAS regression plot (minimum error indicator) and minimum of PRESS value. On the base of obtained results, the differences on the adsorption profiles in the time range between 1 and 600s were used to determine mixtures of both compounds by HLA/GO method. The calculation of the net analytical signal using HLA/GO method allows determination of several figures of merit like selectivity, sensitivity, analytical sensitivity and limit of detection, for each component. To check the ability of the proposed method in the selection of linear regions of adsorption profile, a test for detecting non-linear regions of adsorption profile data in the presence of methanol was also described. The results showed that the method was successfully applied for the determination of ethanol and water.
Keywords: Quartz crystal nanobalance (QCN); Net analyte signal-based method; Ethanol
Determination of azoxystrobin residues in grapes, musts and wines with a multicommuted flow-through optosensor implemented with photochemically induced fluorescence by Javier López Flores; Antonio Molina Díaz; María L. Fernández de Córdova (pp. 185-191).
In this paper, the conversion of azoxystrobin in a strongly fluorescent degradation product by UV irradiation with quantitative purposes and its fluorimetric determination are reported for the first time. A multicommuted flow injection-solid phase spectroscopy (FI-SPS) system combined with photochemically-induced fluorescence (PIF) is developed for the determination of azoxystrobin in grapes, must and wine. Grape samples were homogenized and extracted with methanol and further cleaned-up by solid-phase extraction on C18 silica gel. Wine samples were solid-phase extracted on C18 sorbent using dichloromethane as eluent. Recoveries of azoxystrobin from spiked grapes (0.5–2.0mgKg−1), must (0.5–2.0μgmL−1) and wine (0.5–2.0μgmL−1) were 84.0–87.6%, 95.5–105.9% and 88.5–111.2%, respectively. The quantification limit for grapes was 0.021mgKg−1, being within European Union regulations, and 18μgL−1 and 8μgL−1 for must and wine, respectively.
Keywords: Azoxystrobin; Optosensor; Photochemically induced fluorescence; Multicommutation; Grapes; Must; Wine
Determination of azoxystrobin residues in grapes, musts and wines with a multicommuted flow-through optosensor implemented with photochemically induced fluorescence by Javier López Flores; Antonio Molina Díaz; María L. Fernández de Córdova (pp. 185-191).
In this paper, the conversion of azoxystrobin in a strongly fluorescent degradation product by UV irradiation with quantitative purposes and its fluorimetric determination are reported for the first time. A multicommuted flow injection-solid phase spectroscopy (FI-SPS) system combined with photochemically-induced fluorescence (PIF) is developed for the determination of azoxystrobin in grapes, must and wine. Grape samples were homogenized and extracted with methanol and further cleaned-up by solid-phase extraction on C18 silica gel. Wine samples were solid-phase extracted on C18 sorbent using dichloromethane as eluent. Recoveries of azoxystrobin from spiked grapes (0.5–2.0mgKg−1), must (0.5–2.0μgmL−1) and wine (0.5–2.0μgmL−1) were 84.0–87.6%, 95.5–105.9% and 88.5–111.2%, respectively. The quantification limit for grapes was 0.021mgKg−1, being within European Union regulations, and 18μgL−1 and 8μgL−1 for must and wine, respectively.
Keywords: Azoxystrobin; Optosensor; Photochemically induced fluorescence; Multicommutation; Grapes; Must; Wine