Check out our New Publishers' Select for Free Articles

Analytica Chimica Acta (v.665, #2)

Editorial Board (pp. i).

On-chip integrated multi-thermo-actuated microvalves of poly(N-isopropylacrylamide) for microflow injection analysis by Zhiming Li; Qiaohong He; Dan Ma; Hengwu Chen (pp. 107-112).

An array of thermo-actuated poly(N-isopropylacrylamide) (PNIPAAm) multivalves was designed and fabricated to perform volume-based sample injection for microflow injection analysis on a glass microfluidic chip. The PNIPAAm monolithic plug valves were prepared inside the vinylized glass channels by photopolymerization in water–ethanol (1:1) medium using 2-hydroxy-2-methyl propiophenone (Darocure-1173) as the initiator and a photo-mask for micropattern transferring. Experimental conditions for the photopolymerization were studied, and the thermo-responsive behavior of the synthesized monolithic plug valves was investigated. To perform active heating and cooling of the on-chip integrated thermo-actuated valves, micro-Peltier devices were used and operation times of 3-s for opening and 7-s for closing were obtained. In the close status, a 2-mm long monolithic plug valve could endure a pressure of no higher than 0.45MPa. The volume-based sample and reagent injector was composed of two groups of valves (total valve number of 5) and two loops. When the two groups of valves were alternatively opened and closed via thermo-actuation, the sampling loops were able to be switched between loading and injection position without any mechanical moving parts. Cooperating with syringe pumps, the microfluidic chip with the integrated sample injector has been demonstrated for microflow injection chemiluminescence detection of hydrogen peroxide. For a sampling volume of 6nL, linear response was observed over the H₂O₂ concentration range of 0–2mmolL⁻¹, and a precision of 0.6% (RSD, n=11) was achieved for a standard H₂O₂ solution 2mmolL⁻¹.

Keywords: Micro-flow-injection analysis; Thermo-actuated valves; Volume-based sampling; Poly(N-isopropylacrylamide)

Analytical methodologies for the determination of nitroimidazole residues in biological and environmental liquid samples: A review by Cristina Mahugo-Santana; Zoraida Sosa-Ferrera; M Esther Torres-Padrón; José Juan Santana-Rodríguez (pp. 113-122).

Nitroimidazoles (NDZs) are antiprotozoal drugs that are typically used in veterinary and human medicine. NDZs and their metabolites are believed to possess genotoxic, carcinogenic and mutagenic properties, and this is (one reason) why their use has been banned within the European Union. Hence, the determination of trace residues of these substances in edible animal tissues has been of growing concern over the past few years. Even, though there has been a need to develop sensitive and reliable analytical methods to study the residues of these compounds in different matrices, available methodologies in environmental samples are rather limited. These and other pharmaceutical compounds have become one of the most important new classes of environmental pollutants that have been detected in wastewater-treatment-plant (WWTP) effluents, receiving waters, drinking water and groundwater. A compilation of the most representative analytical methodologies for the determination of NDZ residues during the last decade is presented in this paper. Its scope is the two main areas which require their determination, namely biological and environmental matrices. A detailed explanation of both areas, including sample treatment and detection systems, and future trends is presented, focusing on the difficulties of confirming analytes at low concentration levels.

Keywords: Pharmaceutical products; Nitroimidazoles; Detection systems; Biological samples; Water samples

Low volume microwave digestion and direct determination of selenium in biological samples by hydride generation-atomic fluorescence spectrometry by Qiu-Xiang Zhao; Yu-Wei Chen; Nelson Belzile; Mohui Wang (pp. 123-128).

A low volume microwave digestion (LVMWD) procedure has been developed to have all forms of selenium (Se) compounds in biological samples decomposed to Se (IV) and allow total Se be directly determined by hydride generation-atomic fluorescence spectrometry (HG-AFS), or voltammetrically. Between 0.3 and 0.4mL of mixed digestion reagents consisting of concentrated (15.4M) HNO₃–(18.5M) H₂SO₄ (v:v=10:1) and >5 to <40mg sample were found ideal systems with an optimized MW digestion program. Total Se in five certified reference materials was accurately determined. The results obtained by the conventional and LVMWD techniques agreed well. By avoiding pre-reduction step, this method, suitable for a wide range of biological samples, fully takes the advantages of HG-AFS or voltammetric techniques for their high sensitivity, high tolerance to matrix-related interference and accessibility in instrumentation. LVMWD not only enhances the sample output by 3 times and reduces the operational cost and acid wastes, but also makes the small sample analysis possible for many environmental and medical related research objectives. The digestion pathways of Se containing organic samples are also discussed based on the experimental results.

Keywords: Se determination; Biological samples; Low volume microwave digestion; Hydride generation-atomic fluorescence spectrometry, digestion mechanism

A tutorial on support vector machine-based methods for classification problems in chemometrics by Jan Luts; Fabian Ojeda; Raf Van de Plas; Bart De Moor; Sabine Van Huffel; Johan A.K. Suykens (pp. 129-145).

This tutorial provides a concise overview of support vector machines and different closely related techniques for pattern classification. The tutorial starts with the formulation of support vector machines for classification. The method of least squares support vector machines is explained. Approaches to retrieve a probabilistic interpretation are covered and it is explained how the binary classification techniques can be extended to multi-class methods. Kernel logistic regression, which is closely related to iteratively weighted least squares support vector machines, is discussed. Different practical aspects of these methods are addressed: the issue of feature selection, parameter tuning, unbalanced data sets, model evaluation and statistical comparison. The different concepts are illustrated on three real-life applications in the field of metabolomics, genetics and proteomics.

Keywords: Abbreviations; ARD; automatic relevance determination; AUC; area under the receiver operating characteristic curve; BER; balanced error rate; KLR; kernel logistic regression; LOO; leave-one-out; LS-SVM; least squares support vector machine; MALDI-TOF; matrix-assisted laser desorption ionization time-of-flight; MLP; multilayer perceptron; MR; magnetic resonance; MRI; magnetic resonance imaging; MRS; magnetic resonance spectroscopy; MRSI; magnetic resonance spectroscopic imaging; MSI; mass spectral imaging; RBF; radial basis function; RFE; recursive feature elimination; ROC; receiver operating characteristic; SVM; support vector machine; TF; transcription factor; TOF; time of flight; VUS; volume under the surfaceSupport vector machine; Least squares support vector machine; Kernel logistic regression; Kernel-based learning; Feature selection; Multi-class probabilities

A novel tyrosinase biosensor based on hydroxyapatite–chitosan nanocomposite for the detection of phenolic compounds by Limin Lu; Li Zhang; Xiaobing Zhang; Shuangyan Huan; Guoli Shen; Ruqin Yu (pp. 146-151).

A novel tyrosinase biosensor based on hydroxyapatite nanoparticles (nano-HA)-chitosan nanocomposite has been developed for the detection of phenolic compounds. The uniform and size controlled nano-HA was synthesized by hydrothermal method, and its morphological characterization was examined by transmission electron microscope (TEM). Tyrosinase was then immobilized on a nano-HA-chitosan nanocomposite-modified gold electrode. Electrochemical impedance spectroscopy and cyclic voltammetry were used to characterize the sensing film. The prepared biosensor was applied to determine phenolic compounds by monitoring the reduction signal of the biocatalytically produced quinone species at −0.2V (vs. saturated calomel electrode). The effects of the pH, temperature and applied potential on the biosensor performance were investigated, and experimental conditions were optimized. The biosensor exhibited a linear response to catechol over a wide concentration range from 10nM to 7μM, with a high sensitivity of 2.11×10³μAmM⁻¹cm⁻², and a limit of detection down to 5nM (based on S/N=3). The apparent Michaelis–Menten constants of the enzyme electrode were estimated to be 3.16, 1.31 and 3.52μM for catechol, phenol and m-cresol, respectively. Moreover, the stability and reproducibility of this biosensor were evaluated with satisfactory results.

Keywords: Hydroxyapatite; Tyrosinase; Biosensors; Phenolic compounds; Chitosan

Preparation of metal nanoband microelectrode on poly(dimethylsiloxane) for chip-based amperometric detection by Shao-Peng Chen; Jian Wu; Xiao-Dong Yu; Jing-Juan Xu; Hong-Yuan Chen (pp. 152-159).

We proposed herein a novel approach for fabricating nanoband microelectrodes for electrochemical detection on an electrophoresis microchip. The metal films were first obtained via region-selective electroless deposition of gold or copper films on PDMS substrates by selective region plasma oxidation through shadow masking. Both metal films show uniform surfaces with the thickness at the level of 100nm. By casting another PDMS layer on the metal films, the cross section of the sandwich structures can be used as nanoband microelectrodes, which can be renewed just by cutting. These nanoband microelectrodes are successfully used as electrochemical detectors in microchip electrophoresis for the detection of amino acids, proteins and neurotransmitter molecules. Moreover, integrating an Au-Cu double-metal detector with a double-channel electrophoresis system, we can easily distinguish electroactive amino acids from that of non-electroactive amino acids.

Keywords: Microfluidic chip; Electrophoresis; Amperometric detection; Electroless plating

Comparison and validation of calibration methods for in vivo SPME determinations using an artificial vein system by Joanne Chung Yan Yeung; Dajana Vuckovic; Janusz Pawliszyn (pp. 160-166).

The success of in vivo solid phase microextraction (SPME) depends significantly on the selection of calibration method. Three kinetic in vivo SPME calibration methods are evaluated in this paper: (1) on-fibre standardization (OFS), (2) dominant pre-equilibrium desorption (DPED), and (3) the diffusion-based interface (DBI) model. These are compared in terms of precision, accuracy, and ease of experimental use by employing a flow device simulating an animal circulatory system. In addition, the kinetic calibration methods were validated against established SPME equilibrium extraction (EE) external calibration and a conventional sample preparation method involving protein precipitation. The comparison was performed using a hydrophilic drug fenoterol as the analyte of interest. Liquid chromatography–tandem mass spectrometry (LC–MS/MS) was used for the determinations. All three kinetic methods compared well with both EE extraction and the conventional method in terms of accuracy (93–119%). In terms of precision, the DBI model had the best precision in whole blood and buffered phosphate saline solution with %RSD similar to the standard techniques (9–15%). DPED had the poorest precision of %RSD (20–30%) possibly due to errors associated with uncertainty in the amount of standard loaded on-fibre and remaining on the fibre after desorption. In addition, incurred errors could result due to the greater number of fibres used in comparison to the other two calibration methods. The precision of the OFS procedure was better than for DPED primarily because the use of multiple fibres is eliminated. In terms of the ease of use for calibration, the DBI model was the simplest and most convenient as it did not require standards once it had been calibrated or the uptake constant was calculated. This research suggests the potential use of DBI model as the best kinetic calibration method for future in-vein blood SPME investigations.

Keywords: SPME; Diffusion-based calibration; On-fibre standardization; Dominant pre-equilibrium desorption; Equilibrium SPME; In vivo; SPME; Protein precipitation

Barium alginate caged Fe₃O₄@C₁₈ magnetic nanoparticles for the pre-concentration of polycyclic aromatic hydrocarbons and phthalate esters from environmental water samples by Shengxiao Zhang; Hongyun Niu; Yaqi Cai; Yali Shi (pp. 167-175).

The hydrophobic octadecyl (C₁₈) functionalized Fe₃O₄ magnetic nanoparticles (Fe₃O₄@C₁₈) were caged into hydrophilic barium alginate (Ba²⁺-ALG) polymers to obtain a novel type of solid-phase extraction (SPE) sorbents, and the sorbents were applied to the pre-concentration of polycyclic aromatic hydrocarbons (PAHs) and phthalate esters (PAEs) pollutants from environmental water samples. The hydrophilicity of the Ba²⁺-ALG cage enhances the dispersibility of sorbents in water samples, and the superparamagnetism of the Fe₃O₄ core facilitates magnetic separation. With the magnetic SPE technique based on the Fe₃O₄@C₁₈@Ba²⁺-ALG sorbents, it requires only 30min to extract trace levels of analytes from 500mL water samples. After the eluate is condensed to 0.5mL, concentration factors for both phenanthrene and di-n-propyl-phthalate are over 500, while for other analytes are about 1000. The recoveries of target compounds are independent of salinity and solution pH under testing conditions. Under optimized conditions, the detection limits for phenanthrene, pyrene, benzo[ a]anthracene, and benzo[ a]pyrene are 5, 5, 3, and 2ngL⁻¹, and for di-n-propyl-phthalate, di-n-butyl-phthalate, di-cyclohexyl-phthalate, and di-n-octyl-phthalate are 36, 59, 19, and 36ngL⁻¹, respectively. The spiked recoveries of several real water samples for PAHs and PAEs are in the range of 72–108% with relative standard deviations varying from 1% to 9%, showing good accuracy of the method. The advantages of the new SPE method include high extraction efficiency, short analysis time and convenient extraction procedure. To the best of our knowledge, it is unprecedented that hydrophilic Ba²⁺-ALG polymer caged Fe₃O₄@C₁₈ magnetic nanomaterial is used to extract organic pollutants from large volumes of water samples.

Keywords: Magnetic nanoparticles; Barium alginate; Solid-phase extraction; Polycyclic aromatic hydrocarbons; Phthalate esters

Monitoring of progestins: Development of immunochemical methods for purification and detection of levonorgestrel by Moran Shalev; Michal Bardugo; Ayelet Nudelman; Alex Krol; Haim Schlesinger; Alisa Bronshtein; Miriam Altstein (pp. 176-184).

A polyclonal antibody (Ab) for the progestin levonorgestrel (LNG) was generated, and immunochemical assays for its detection, clean-up and concentration were developed. A highly specific microplate diagnostic assay for the detection of LNG was developed that used the enzyme linked immunosorbent assay (ELISA) method. The LNG ELISA developed was sensitive and reproducible; it exhibited I₅₀ and I₂₀ values of 3.3±1.8ngmL⁻¹ and 0.6±0.4ngmL⁻¹, respectively, and the Abs did not cross react with any of the tested steroid hormones. The above Abs were used to develop a sol–gel-based immunoaffinity purification (IAP) method for concentration and clean-up of LNG that is compatible with subsequent immunochemical or instrumental chemical analytical procedures, such as liquid chromatography followed by mass spectrometry (LC–MS/MS). Development of the columns included successful entrapment of Abs within a tetramethoxysilane (TMOS)-based SiO₂ polymer network. The Abs could bind the free analyte from solution, and the bound analyte could be easily eluted from the sol–gel matrix at high recoveries. The Ab selectivity towards the antigen was high, in both ELISA and the sol–gel columns, but the entrapped Abs cross-reacted with two other steroid hormones – ethynylestradiol (EE2) and nortestosterone (NT) – which share similar epitopes with LNG, despite the lack of cross reactivity in the ELISA. The validity of the method was investigated by LC–MS/MS and a good analytical correlation was obtained.

Keywords: Abbreviation; ACN; acetonitrile; BSA; bovine serum albumin; CMA; (carboxymethoxy)amine hemihydrochloride; CMO; carboxymethyloxime; DCC; N′,N′-dicyclohexylcarbodiimide; DCM; methylene chloride; DDW; double distilled water; DMF; dimethylformamide; EE2; ethynylestradiol; ELISA; enzyme linked immunosorbent assay; FLX; fluoxetine; GC; gas chromatography; HEPES; 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid; HRP; horseradish peroxidase; IAP; immunoaffinity purification; IMT; indomethacin; KLH; Keyhole Limpet Hemocyanin; LC; liquid chromatography; LNG; levonorgestrel; LOD; limit of detection; MPA; medroxyprogesterone acetate; MRM; multiple reaction monitor; MS; mass spectrometry; NHS; N-hydroxysuccinimide; NSAIDs; non-steroid anti-inflammatory drugs; NT; nortestosterone; ON; overnight; PBS; phosphate-buffered saline; PBST; sodium phosphate containing Tween; PPs; pharmaceutical products; OVA; ovalbumin; PEG; polyethylene glycol; Py; pyridine; RIA; radioimmunoassay; SPE; solid-phase extraction; SSRIs; selective serotonin reuptake inhibitors; TMB; 3,3′,5,5′-tetramethyl benzidine; TMOS; tetramethylsilane; TMP; thrimethoprimLevonorgestrel; Enzyme linked immunosorbent assay; Immunoaffinity chromatography; Sol–gel; Pharmaceutical product residues; Residue monitoring; Endocrine disruptors

Determination of sulfonamides in soil samples based on alumina-coated magnetite nanoparticles as adsorbents by Lei Sun; Xin Sun; Xiaobo Du; Yanshan Yue; Ligang Chen; Haoyan Xu; Qinglei Zeng; Hui Wang; Lan Ding (pp. 185-192).

In this study, alumina-coated magnetite nanoparticles (Fe₃O₄/Al₂O₃ NPs) were synthesized, and they were applied to the analysis of sulfonamides (SAs) including sulfadiazine (SDZ), sulfamerazine (SMR), sulfamethoxazole (SMX), sulfamonomethoxine (SMM), sulfamethoxydiazine (SMD), sulfadimethoxine (SDM) and sulfaquinoxaline (SQX) in different soil samples based on magnetic solid-phase extraction (MSPE). The extraction and concentration process was carried out in a single step by mixing the extraction solvent, magnetic adsorbents and soil sample under ultrasonic action. Then, the adsorbents were isolated from the complicated matrix easily with an external magnetic field. The SAs desorbed from the adsorbents were determined by liquid chromatography–tandem mass spectrometry. Compared with traditional methods, the MSPE method simplified the operation procedure and reduced the analysis time. Under the optimum conditions, the recoveries of SDZ, SMR, SMX, SMM, SMD and SDM by analyzing the five spiked soil samples were between 71% and 93% except for SQX (42–60%). This may be due to the stronger hydrophobic property of SQX. Detection limits of SAs were between 0.37 and 6.74ngg⁻¹. It was also found that the “aging” effect of SAs contaminated soil could cause the recoveries to decrease.

Keywords: Alumina-coated magnetite nanoparticles; Magnetic solid-phase extraction; Sulfonamides; Soil samples

Determination of polycyclic aromatic hydrocarbons in waters by ultrasound-assisted emulsification-microextraction and gas chromatography–mass spectrometry by Senar Ozcan; Ali Tor; Mehmet Emin Aydin (pp. 193-199).

An ultrasound-assisted emulsification-microextraction (USAEME) procedure was developed for the extraction of US EPA 16 polycyclic aromatic hydrocarbons (PAHs) in 10mL of water samples, with subsequent determination by gas chromatography–mass spectrometry (GC–MS). After determination of the most suitable solvent and solvent volume, several other parameters (i.e., extraction time, centrifugation time and ionic strength of the sample) were optimized using a 2³ factorial experimental design. Limits of detection ranged from 0.001 to 0.036μgL⁻¹. The developed procedure was applied to fortified distilled water with different fortification levels (0.5, 2 and 5μgL⁻¹). Recoveries were over 92% and relative standard deviations of the recoveries were below 8%. The efficiency of the USAEME was compared with traditional liquid–liquid extraction (LLE) and solid-phase extraction on real water samples (i.e., tap water, well water and surface (lake) water as well as domestic and industrial wastewaters). The USAEME showed comparable efficiencies especially with LLE. The developed USAEME was demonstrated to be robust, viable, simple, rapid and easy to use for the determination of PAHs in water samples by GC–MS.

Keywords: Polycyclic aromatic hydrocarbons; Ultrasound-assisted emulsification-microextraction; Water analysis; Factorial design

Determination of Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb in seawater using high resolution magnetic sector inductively coupled mass spectrometry (HR-ICP-MS) by Angela Milne; William Landing; Michael Bizimis; Peter Morton (pp. 200-207).

A novel method, combining isotope dilution with standard additions, was developed for the analysis of eight elements (Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb) in seawater. The method requires just 12mL of sample and employs an off-line pre-concentration step using the commercially available chelating resin Toyopearl AF-Chelate-650M prior to determination by high resolution inductively coupled plasma magnetic sector mass spectrometry (ICP-MS). Acidified samples were spiked with a multi-element standard of six isotopes (⁵⁷Fe,⁶²Ni,⁶⁵Cu,⁶⁸Zn,¹¹¹Cd and²⁰⁷Pb) enriched over natural abundance. In addition, standard additions of a mixed Co and Mn standard were performed on sub-sets of the same sample. All samples were irradiated using a low power (119mWcm⁻²; 254nm) UV system, to destroy organic ligands, before pre-concentration and extraction from the seawater matrix. Ammonium acetate was used to raise the pH of the 12mL sub-samples (off-line) to pH 6.4±0.2 prior to loading onto the chelating resin. The extracted metals were eluted using 1.0M Q-HNO₃ and determined using ICP-MS. The method was verified through the analysis of certified reference material (NASS-5) and the SAFe inter-comparison samples (S1 and D2), the results of which are in good agreement with the certified and reported consensus values. We also present vertical profiles of the eight metals taken from the Bermuda Atlantic Time Series (BATS) station collected during the GEOTRACES inter-comparison cruise in June 2008.

Keywords: Trace metals; Seawater; Isotope dilution; HR-ICP-MS

Comparative studies of mercapto thiadiazoles self-assembled on gold nanoparticle as ionophores for Cu(II) carbon paste sensors by Mohammad Hossein Mashhadizadeh; Hadi Khani; Alireza Foroumadi; Parishad Sagharichi (pp. 208-214).

Comparative studies of the potentiometric behavior of three mercapto compounds [2-((5-mercapto-1,3,4-thiadiazol-2-ylimino)methyl)phenol] (MTMP), [5-(2-methoxy benzylidene amino)-1,3,4-thiadiazole-2-thiol] (MBYT) and [5-(pyridin-2-ylmethyleneamino)-1,3,4-thiadiazole-2-thiol] (PYTT) self-assembled on gold nanoparticles (GNPs) as ionophores in carbon paste electrodes (CPEs) have been made. These mercapto thiadiazole compounds were self-assembled onto gold nanoparticles and then incorporated within carbon paste electrode. The self-assembled ionophores exhibit a high selectivity for copper ion (Cu²⁺), in which the sulfur and nitrogen atoms in their structure play a role as the effective coordination donor site for the copper ion. These carbon paste electrodes were applied as indicator electrodes for potentiometric determination of copper ions. The sensor based on PYTT exhibits the working concentration range of 4.0×10⁻⁹ to 7.0×10⁻²M and a Nernstian slope of 28.7±0.3mVdecade⁻¹ of copper activity. The detection limit of electrode was 1.0×10⁻⁹M and potential response was pH independent across the range of 3.0–6.5. It exhibited a quick response time of <5s and could be used for a period of 45 days. The ion selectivity of this electrode for Cu²⁺ was over 10⁴ times that for other metal cations. The application of prepared sensors has been demonstrated for the determination of copper ions in spiked water and natural water samples.

Keywords: Gold nanoparticle; Self-assembly; Mercapto compound; Potentiometric sensor; Carbon paste electrode; Copper ion

Photophysical properties of rhodamine isomers: A two-photon excited fluorescent sensor for trivalent chromium cation (Cr³⁺) by Yan Wan; Qianjin Guo; Xuefei Wang; Andong Xia (pp. 215-220).

We introduce a new rhodamine-based fluorescent chemosensor, FD8 which exhibits a distinct two-photon excited fluorescence (TPEF) on/off characteristic upon binding Cr³⁺ ions. By coordination with metal cation, conformation of FD8 changes from spirocyclic to open-ring, resulting in remarkable enhancement of absorption and fluorescence both in one- and two-photon excitations. As a result, a 29-fold enhancement of two-photon excited fluorescent intensity was observed when 10eq. Cr³⁺ was added to the FD8 solution. The detection limit of Cr³⁺ cation concentration down to 1μM (0.01eq. of FD8) was achieved under our experimental condition. Besides the excitation within ultraviolet regime by fluorescence resonance energy transfer (FRET) mechanism, the TPEF on/off behavior further extends the excitation to near infrared regime (the biological optimal window of 700–1200nm), and shows more effective sensitivity. The broad excitation wavelength, on/off fluorescence and high selectivity to Cr³⁺ enable FD8 to be a powerful Cr³⁺ cation sensor with potential application, especially in biological detection. To the best of our knowledge, this is the first report about two-photon fluorescent sensor for Cr³⁺ ions.

Keywords: Two-photon excitation; Fluorescent sensor; Trivalent chromium ion (Cr; ³⁺; ); Rhodamine; Fluorescence on/off

Hollow fiber-based liquid phase microextraction combined with high-performance liquid chromatography for the analysis of gabapentin in biological samples by Homeira Ebrahimzadeh; Yadollah Yamini; Hamid Abedi Firozjaei; Fahimeh Kamarei; Najmeh Tavassoli; Mohammad Reza Rouini (pp. 221-226).

Three-phase hollow fiber microextraction technique combined with high performance liquid chromatography-ultra violet (HPLC-UV) was applied for the extraction and determination of gabapentin in biological fluids. Gabapentin (GBP) was derivatized with 1-fluoro-2,4-dinitrobenzene, as a UV absorbent agent in borate buffer (pH 8.2) before extraction. The derivative product of GBP was extracted from the 8.5mL of acidic solution (source phase) into an organic phase (dihexyl ether) impregnated in the pores of a hollow fiber and finally back-extracted into 24μL of the basic solution (pH 9.1) located inside the lumen of the hollow fiber (receiving phase). The extraction took place due to pH gradient between the inside and outside of the hollow fiber membrane. In order to achieve maximum extraction efficiency, different parameters affecting the extraction conditions were optimized. Under the optimized conditions, preconcentration factor of 95 and detection limit (LOD) of 0.2μgL⁻¹ were obtained. The calibration graph was linear within the range of 0.6–5000μgL⁻¹. Finally, the feasibility of the proposed method was successfully confirmed by extraction and determination of GBP in human urine and plasma samples in the range of microgram per liter and suitable results were obtained (RSDs<6.3%).

Keywords: Three-phase hollow fiber microextraction; Gabapentin; Derivatization; High performance liquid chromatography

A rapid, acetonitrile-free, HPLC method for determination of melamine in infant formula by Gopalakrishnan Venkatasami; John R. Sowa Jr. (pp. 227-230).

A simple, precise, accurate and validated, acetonitrile-free, reverse phase high performance liquid chromatography (HPLC) method is developed for the determination of melamine in dry and liquid infant formula. The separation is performed on a Kromasil C18 column (150mm×3.2mm I.D., 5μm particle size) at room temperature. The mobile phase (0.1% TFA/methanol 90:10) is pumped at a flow rate of 0.3mLmin⁻¹ with detection at 240nm. Melamine elutes at 3.7min. A linear response ( r>0.999) is observed for samples ranging from 1.0 to 80μgmL⁻¹. The method provides recoveries of 97.2–101.2% in the concentration range of 5–40μgmL⁻¹, intra- and inter-day variation in <1.0% R.S.D. The limit of detection (LOD) and limit of quantification (LOQ) values are 0.1μgmL⁻¹ and 0.2μgmL⁻¹, respectively.

Keywords: Melamine; High performance liquid chromatography (HPLC); Infant formula; Validation; Acetonitrile-free

Pressurised hot water extraction followed by simultaneous derivatization and headspace solid-phase microextraction and gas chromatography-tandem mass spectrometry for the determination of aliphatic primary amines in sewage sludge by Anna Llop; Francesc Borrull; Eva Pocurull (pp. 231-236).

In this paper we describe an environmentally friendly and sensitive method for the determination of ten primary amines in sewage sludge. The method is based on pressurised hot water extraction (PHWE) followed by simultaneous derivatization with pentafluorobenzaldehyde (PFBAY) and headspace solid-phase microextraction (HS-SPME) and subsequent gas-chromatography ion-trap tandem mass spectrometry (GC-IT-MS–MS) analysis. The influence of the main factors on the PHWE of sludge was optimized by a central composite design. For all species the optimal conditions were water at pH 4 as the extracting solvent, an extraction temperature of 100°C and an extraction time of 15min. The separation and detection of the ten amines by GC-IT-MS–MS took just 10min and the entire process took approximately 1h. Repeatability and reproducibility between days, expressed as RSD (%) ( n=5), were less than 19 and 24%, respectively. The average limit of detection (LOD) was of 65μgkg⁻¹s (range found 9–135) and the average limit of quantification (LOQ) was of 230μgkg⁻¹ (range found 50–450) of dry weight (d.w.). Under optimized conditions we used this method to determine the compounds in industrial and municipal sewage sludge samples and in sludge from a potable water treatment plant. Methylamine and isobutylamine showed the highest levels in one of the industrial sewage sludge samples (404 and 543mgkg⁻¹ (d.w.), respectively). To our knowledge, this paper presents for the first time the determination of ten primary amines in sewage sludge samples using PHWE.

Keywords: Primary aliphatic amines; Sewage sludge; Pressurised hot water extraction; Solid-phase microextraction; Gas chromatography–mass spectrometry–mass spectrometry; Central composite design

Sections

Personal tools

Analytica Chimica Acta (v.665, #2)

Sections

Personal tools

Local resources

Analytica Chimica Acta (v.665, #2)