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Analytica Chimica Acta (v.579, #1)
Pattern recognition analysis of differential mobility spectra with classification by chemical family by G.A. Eiceman; M. Wang; S. Prasad; H. Schmidt; F.K. Tadjimukhamedov; Barry K. Lavine; Nikhil Mirjankar (pp. 1-10).
Differential mobility spectra for alkanes, alcohols, ketones, cycloalkanes, substituted ketones, and substituted benzenes with carbon numbers between 3 and 10 were obtained from gas chromatography-differential mobility spectrometry (GC-DMS) analyses of mixtures in dilute solution. Spectra were produced in a supporting atmosphere of purified air with 0.6–0.8ppm moisture, gas temperature of 120°C, sample concentrations of ∼0.2–5ppm, and ion source of 5mCi (185MBq)63Ni. Multiple spectra were extracted from chromatographic elution profiles for each chemical providing a library of 390 spectra from 39 chemicals. The spectra were analyzed for structural content by chemical family using two different approaches. In the one approach, the wavelet packet transform was used to denoise and deconvolute the DMS data by decomposing each spectrum into its wavelet coefficients, which represent the sample's constituent frequencies. The wavelet coefficients characteristic of the compound's structural class were identified using a genetic algorithm (GA) for pattern recognition analysis. The pattern recognition GA uses both supervised and unsupervised learning to identify coefficients which optimize clustering of the spectra in a plot of the two or three largest principal components of the data. Because principal components maximize variance, the bulk of the information encoded by the selected coefficients is about differences between chemical families in the data set. The principal component analysis routine embedded in the fitness function of the pattern recognition GA acts as an information filter, significantly reducing the size of the search space since it restricts the search to coefficients whose principal component plots show clustering on the basis of chemical family. In a second approach, a back propagation neural network was trained to categorize spectra by chemical families and the network was successfully tested using familiar and unfamiliar chemicals. Performance of the network was associated with a region of the spectrum associated with fragment ions which could be extracted from spectra and were class specific.
Keywords: Differential mobility spectrometer; Fragment ions; Feature selection; Wavelets; Genetic algorithms; Neural networks; Classification; Pattern recognition
Pattern recognition analysis of differential mobility spectra with classification by chemical family by G.A. Eiceman; M. Wang; S. Prasad; H. Schmidt; F.K. Tadjimukhamedov; Barry K. Lavine; Nikhil Mirjankar (pp. 1-10).
Differential mobility spectra for alkanes, alcohols, ketones, cycloalkanes, substituted ketones, and substituted benzenes with carbon numbers between 3 and 10 were obtained from gas chromatography-differential mobility spectrometry (GC-DMS) analyses of mixtures in dilute solution. Spectra were produced in a supporting atmosphere of purified air with 0.6–0.8ppm moisture, gas temperature of 120°C, sample concentrations of ∼0.2–5ppm, and ion source of 5mCi (185MBq)63Ni. Multiple spectra were extracted from chromatographic elution profiles for each chemical providing a library of 390 spectra from 39 chemicals. The spectra were analyzed for structural content by chemical family using two different approaches. In the one approach, the wavelet packet transform was used to denoise and deconvolute the DMS data by decomposing each spectrum into its wavelet coefficients, which represent the sample's constituent frequencies. The wavelet coefficients characteristic of the compound's structural class were identified using a genetic algorithm (GA) for pattern recognition analysis. The pattern recognition GA uses both supervised and unsupervised learning to identify coefficients which optimize clustering of the spectra in a plot of the two or three largest principal components of the data. Because principal components maximize variance, the bulk of the information encoded by the selected coefficients is about differences between chemical families in the data set. The principal component analysis routine embedded in the fitness function of the pattern recognition GA acts as an information filter, significantly reducing the size of the search space since it restricts the search to coefficients whose principal component plots show clustering on the basis of chemical family. In a second approach, a back propagation neural network was trained to categorize spectra by chemical families and the network was successfully tested using familiar and unfamiliar chemicals. Performance of the network was associated with a region of the spectrum associated with fragment ions which could be extracted from spectra and were class specific.
Keywords: Differential mobility spectrometer; Fragment ions; Feature selection; Wavelets; Genetic algorithms; Neural networks; Classification; Pattern recognition
Analysis of arsenic and calcium in soil samples by laser ablation mass spectrometry by Ana M. Beccaglia; Carlos A. Rinaldi; Juan C. Ferrero (pp. 11-16).
We present an analytical procedure based on laser ablation mass spectrometry (LAMS) in order to detect and quantify arsenic and calcium in soil samples and we analyze the diverse factors that influence the precision of LAMS, such as laser fluence and matrix effect. The results indicate that a Zn matrix is a good choice for the analysis of those metals in soil samples. This work also provides a method for the direct determination of As in soil samples whose concentrations are lower than 100ppm with a 70ppm minimum detection limits (MDL).
Keywords: Laser ablation; Mass spectrometry; Elemental analysis; Soil sample; Calcium; Arsenic
Analysis of arsenic and calcium in soil samples by laser ablation mass spectrometry by Ana M. Beccaglia; Carlos A. Rinaldi; Juan C. Ferrero (pp. 11-16).
We present an analytical procedure based on laser ablation mass spectrometry (LAMS) in order to detect and quantify arsenic and calcium in soil samples and we analyze the diverse factors that influence the precision of LAMS, such as laser fluence and matrix effect. The results indicate that a Zn matrix is a good choice for the analysis of those metals in soil samples. This work also provides a method for the direct determination of As in soil samples whose concentrations are lower than 100ppm with a 70ppm minimum detection limits (MDL).
Keywords: Laser ablation; Mass spectrometry; Elemental analysis; Soil sample; Calcium; Arsenic
Univariate near infrared methods for determination of pesticides in agrochemicals by Javier Moros; Sergio Armenta; Salvador Garrigues; Miguel de la Guardia (pp. 17-24).
It has been developed a general strategy for the determination of pesticides in agrochemicals by Fourier transform near infrared (FT-NIR) spectroscopy. The methodology is based on previous extraction of the active principles through sonication with acetonitrile and direct determination by transmission measurements, using glass vials as measurement cells and univariate calibration at selected wavenumbers as a function of the pesticide to be analyzed. Chlorsulfuron, metamitron, iprodione, pirimicarb, procymidone and tricyclazole were used as test molecules and data obtained by FT-NIR for 20 samples containing one of these active principles compare well with those found by reference liquid chromatography (HPLC) procedures. In short, FT-NIR provides relative standard deviations between 0.04 and 0.7% and limit of detection values ranging from 0.004 to 0.17mgg−1 with recovery values between 96.4 and 100.5%. On the other hand, FT-NIR offers a 10 times faster methodology than chromatography ones and an environmentally friendly alternative which reduces the reagent consumption to 1mL acetonitrile per sample.
Keywords: Near infrared; Pesticide formulations; Chlorsulfuron; Metamitron; Iprodione; Pirimicarb; Procymidone; Tricyclazole
Univariate near infrared methods for determination of pesticides in agrochemicals by Javier Moros; Sergio Armenta; Salvador Garrigues; Miguel de la Guardia (pp. 17-24).
It has been developed a general strategy for the determination of pesticides in agrochemicals by Fourier transform near infrared (FT-NIR) spectroscopy. The methodology is based on previous extraction of the active principles through sonication with acetonitrile and direct determination by transmission measurements, using glass vials as measurement cells and univariate calibration at selected wavenumbers as a function of the pesticide to be analyzed. Chlorsulfuron, metamitron, iprodione, pirimicarb, procymidone and tricyclazole were used as test molecules and data obtained by FT-NIR for 20 samples containing one of these active principles compare well with those found by reference liquid chromatography (HPLC) procedures. In short, FT-NIR provides relative standard deviations between 0.04 and 0.7% and limit of detection values ranging from 0.004 to 0.17mgg−1 with recovery values between 96.4 and 100.5%. On the other hand, FT-NIR offers a 10 times faster methodology than chromatography ones and an environmentally friendly alternative which reduces the reagent consumption to 1mL acetonitrile per sample.
Keywords: Near infrared; Pesticide formulations; Chlorsulfuron; Metamitron; Iprodione; Pirimicarb; Procymidone; Tricyclazole
Least-squares support vector machines and near infrared spectroscopy for quantification of common adulterants in powdered milk by Alessandra Borin; Marco Flôres Ferrão; Cesar Mello; Danilo Althmann Maretto; Ronei Jesus Poppi (pp. 25-32).
This paper proposes the use of the least-squares support vector machine (LS-SVM) as an alternative multivariate calibration method for the simultaneous quantification of some common adulterants (starch, whey or sucrose) found in powdered milk samples, using near-infrared spectroscopy with direct measurements by diffuse reflectance. Due to the spectral differences of the three adulterants a nonlinear behavior is present when all groups of adulterants are in the same data set, making the use of linear methods such as partial least squares regression (PLSR) difficult. Excellent models were built using LS-SVM, with low prediction errors and superior performance in relation to PLSR. These results show it possible to built robust models to quantify some common adulterants in powdered milk using near-infrared spectroscopy and LS-SVM as a nonlinear multivariate calibration procedure.
Keywords: Powdered milk; Adulterants; Multivariate calibration; Support vector machines
Least-squares support vector machines and near infrared spectroscopy for quantification of common adulterants in powdered milk by Alessandra Borin; Marco Flôres Ferrão; Cesar Mello; Danilo Althmann Maretto; Ronei Jesus Poppi (pp. 25-32).
This paper proposes the use of the least-squares support vector machine (LS-SVM) as an alternative multivariate calibration method for the simultaneous quantification of some common adulterants (starch, whey or sucrose) found in powdered milk samples, using near-infrared spectroscopy with direct measurements by diffuse reflectance. Due to the spectral differences of the three adulterants a nonlinear behavior is present when all groups of adulterants are in the same data set, making the use of linear methods such as partial least squares regression (PLSR) difficult. Excellent models were built using LS-SVM, with low prediction errors and superior performance in relation to PLSR. These results show it possible to built robust models to quantify some common adulterants in powdered milk using near-infrared spectroscopy and LS-SVM as a nonlinear multivariate calibration procedure.
Keywords: Powdered milk; Adulterants; Multivariate calibration; Support vector machines
A membraneless gas diffusion unit: Design and its application to determination of ethanol in liquors by spectrophotometric flow injection by N. Choengchan; T. Mantim; P. Wilairat; P.K. Dasgupta; S. Motomizu; D. Nacapricha (pp. 33-37).
This work presents new design of a gas diffusion unit, called ‘membraneless gas diffusion (MGD) unit’, which, unlike a conventional gas diffusion (GD) unit, allows selective detection of volatile compounds to be made without the need of a hydrophobic membrane. A flow injection method was developed employing the MGD unit to determine ethanol in alcoholic drinks based on the reduction of dichromate by ethanol vapor. Results clearly demonstrated that the MGD unit was suitable for determination of ethanol in beer, wine and distilled liquors. Detection limit (3S/N) of MGD unit was lower than the GD unit (GD: 0.68%, v/v; MGD: 0.27%, v/v). The MGD design makes the system more sensitive as mass transfer is more efficient than that of GD and thus, MGD can perfectly replace membrane-based designs.
Keywords: Membraneless gas diffusion; Flow injection; Ethanol determination; Liquor; Spectrophotometry
A membraneless gas diffusion unit: Design and its application to determination of ethanol in liquors by spectrophotometric flow injection by N. Choengchan; T. Mantim; P. Wilairat; P.K. Dasgupta; S. Motomizu; D. Nacapricha (pp. 33-37).
This work presents new design of a gas diffusion unit, called ‘membraneless gas diffusion (MGD) unit’, which, unlike a conventional gas diffusion (GD) unit, allows selective detection of volatile compounds to be made without the need of a hydrophobic membrane. A flow injection method was developed employing the MGD unit to determine ethanol in alcoholic drinks based on the reduction of dichromate by ethanol vapor. Results clearly demonstrated that the MGD unit was suitable for determination of ethanol in beer, wine and distilled liquors. Detection limit (3S/N) of MGD unit was lower than the GD unit (GD: 0.68%, v/v; MGD: 0.27%, v/v). The MGD design makes the system more sensitive as mass transfer is more efficient than that of GD and thus, MGD can perfectly replace membrane-based designs.
Keywords: Membraneless gas diffusion; Flow injection; Ethanol determination; Liquor; Spectrophotometry
Determination of hydrogen sulfide and volatile thiols in air samples by mercury probe derivatization coupled with liquid chromatography–atomic fluorescence spectrometry by Emilia Bramanti; Lucia D’Ulivo; Cristina Lomonte; Massimo Onor; Roberto Zamboni; Giorgio Raspi; Alessandro D’Ulivo (pp. 38-46).
A new procedure is proposed for the sampling and storage of hydrogen sulphide (H2S) and volatile thiols (methanethiol or methyl mercaptan, ethanethiol and propanethiol) for their determination by liquid chromatography. The sampling procedure is based on the trapping/pre-concentration of the analytes in alkaline aqueous solution containing an organic mercurial probe p-hydroxymercurybenzoate, HO–Hg–C6H4–COO− (PHMB), where they are derivatized to stable PHMB complexes based on mercury–sulfur covalent bonds. PHMB complexes are separated on a C18 reverse phase column, allowing their determination by liquid chromatography coupled with sequential non-selective UV–vis (DAD) and mercury specific (chemical vapor generation atomic fluorescence spectrometry, CVGAFS) on-line detectors. PHMB complexes, S(PHMB)2CH3S-PHMB, C2H5S-PHMB and C3H7S-PHMB, are stable alt least for 12h at room temperature and for 3 months if stored frozen (−20°C).The best analytical figures of merits in the optimized conditions were obtained by CVGAFS detection, with detection limits (LODc) of 9.7μgL−1 for H2S, 13.7μgL−1 for CH3SH, 17.7μgL−1 for C2H5SH and 21.7μgL−1 for C3H7SH in the trapping solution in form of RS-PHMB complexes, the relative standard deviation (R.S.D.) ranging between 1.0 and 1.5%, and a linear dynamic range (LDR) between 10 and 9700μgL−1. Conventional UV absorbance detectors tuned at 254nm can be employed as well with comparable R.S.D. and LDR, but with LODc one order of magnitude higher than AFS detector and lower specificity. The sampling procedure followed by LC–DAD-CVGAFS analysis has been validated, as example, for H2S determination by a certified gas permeation tube as a source of 3.071±0.154μgmin−1 of H2S, giving a recovery of 99.8±7% and it has been applied to the determination of sulfur compounds in real gas samples (biogas and the air of a plant for fractional distillation of crude oil).
Keywords: Sampling; Environmental analysis; Reduced sulfur compounds; Sulfur speciation; Liquid chromatography; Thiols; Hyphenated technique
Determination of hydrogen sulfide and volatile thiols in air samples by mercury probe derivatization coupled with liquid chromatography–atomic fluorescence spectrometry by Emilia Bramanti; Lucia D’Ulivo; Cristina Lomonte; Massimo Onor; Roberto Zamboni; Giorgio Raspi; Alessandro D’Ulivo (pp. 38-46).
A new procedure is proposed for the sampling and storage of hydrogen sulphide (H2S) and volatile thiols (methanethiol or methyl mercaptan, ethanethiol and propanethiol) for their determination by liquid chromatography. The sampling procedure is based on the trapping/pre-concentration of the analytes in alkaline aqueous solution containing an organic mercurial probe p-hydroxymercurybenzoate, HO–Hg–C6H4–COO− (PHMB), where they are derivatized to stable PHMB complexes based on mercury–sulfur covalent bonds. PHMB complexes are separated on a C18 reverse phase column, allowing their determination by liquid chromatography coupled with sequential non-selective UV–vis (DAD) and mercury specific (chemical vapor generation atomic fluorescence spectrometry, CVGAFS) on-line detectors. PHMB complexes, S(PHMB)2CH3S-PHMB, C2H5S-PHMB and C3H7S-PHMB, are stable alt least for 12h at room temperature and for 3 months if stored frozen (−20°C).The best analytical figures of merits in the optimized conditions were obtained by CVGAFS detection, with detection limits (LODc) of 9.7μgL−1 for H2S, 13.7μgL−1 for CH3SH, 17.7μgL−1 for C2H5SH and 21.7μgL−1 for C3H7SH in the trapping solution in form of RS-PHMB complexes, the relative standard deviation (R.S.D.) ranging between 1.0 and 1.5%, and a linear dynamic range (LDR) between 10 and 9700μgL−1. Conventional UV absorbance detectors tuned at 254nm can be employed as well with comparable R.S.D. and LDR, but with LODc one order of magnitude higher than AFS detector and lower specificity. The sampling procedure followed by LC–DAD-CVGAFS analysis has been validated, as example, for H2S determination by a certified gas permeation tube as a source of 3.071±0.154μgmin−1 of H2S, giving a recovery of 99.8±7% and it has been applied to the determination of sulfur compounds in real gas samples (biogas and the air of a plant for fractional distillation of crude oil).
Keywords: Sampling; Environmental analysis; Reduced sulfur compounds; Sulfur speciation; Liquid chromatography; Thiols; Hyphenated technique
Determination of trace impurities in high-purity zirconium dioxide by inductively coupled plasma atomic emission spectrometry using microwave-assisted digestion and wavelet transform-based correction procedure by Xiaoguo Ma; Yibing Li (pp. 47-52).
This paper describes a rapid, accurate and precise method for the determination of trace Fe, Hf, Mn, Na, Si and Ti in high-purity zirconium dioxide (ZrO2) powders by inductively coupled plasma atomic emission spectrometry (ICP-AES). The samples were dissolved by a microwave-assisted digestion system. Four different digestion programs with various reagents were tested. It was found that using a mixture of sulfuric acid (H2SO4) and ammonium sulfate ((NH4)2SO4), the total sample dissolution time was 30min, much shorter than that required for conventional digestion in an opening system. The determination of almost all of the target analytes suffered from spectral interferences, since Zr shows a line-rich atomic emission spectrometry. The wavelet transform (WT), a recently developed mathematical technique was applied to the correction of spectral interference, and more accurate and precise results were obtained, compared with traditional off-peak background correction procedure. Experimental work revealed that a high Zr concentration would result in a significant decrease in peak height of the analyte lines, which was corrected by standard addition method. The performance of the developed method was evaluated by using synthetic samples. The recoveries were in the range of 87–112% and relative standard deviation was within 1.1–3.4%. The detection limits (3 σ) for Fe, Hf, Mn, Na, Si and Ti were found to be 1.2, 13.3, 1.0, 4.5, 5.8 and 2.0μgg−1, respectively. The results showed that with the microwave-assisted digestion and the WT correction, the detection limits have improved by a factor of about 5 for Fe, 4 for Mn and Ti, 3 for Si, and 2 for Hf and Na, respectively, in comparison with conventional open-system digestion and off-peak correction. The proposed technique was applied to the analysis of trace elements above-mentioned in three types of ZrO2 powders.
Keywords: Zirconium dioxide; Microwave-assisted digestion; Wavelet transform; Inductively coupled plasma atomic emission spectrometry; Trace element analysis; Spectral interference correction
Determination of trace impurities in high-purity zirconium dioxide by inductively coupled plasma atomic emission spectrometry using microwave-assisted digestion and wavelet transform-based correction procedure by Xiaoguo Ma; Yibing Li (pp. 47-52).
This paper describes a rapid, accurate and precise method for the determination of trace Fe, Hf, Mn, Na, Si and Ti in high-purity zirconium dioxide (ZrO2) powders by inductively coupled plasma atomic emission spectrometry (ICP-AES). The samples were dissolved by a microwave-assisted digestion system. Four different digestion programs with various reagents were tested. It was found that using a mixture of sulfuric acid (H2SO4) and ammonium sulfate ((NH4)2SO4), the total sample dissolution time was 30min, much shorter than that required for conventional digestion in an opening system. The determination of almost all of the target analytes suffered from spectral interferences, since Zr shows a line-rich atomic emission spectrometry. The wavelet transform (WT), a recently developed mathematical technique was applied to the correction of spectral interference, and more accurate and precise results were obtained, compared with traditional off-peak background correction procedure. Experimental work revealed that a high Zr concentration would result in a significant decrease in peak height of the analyte lines, which was corrected by standard addition method. The performance of the developed method was evaluated by using synthetic samples. The recoveries were in the range of 87–112% and relative standard deviation was within 1.1–3.4%. The detection limits (3 σ) for Fe, Hf, Mn, Na, Si and Ti were found to be 1.2, 13.3, 1.0, 4.5, 5.8 and 2.0μgg−1, respectively. The results showed that with the microwave-assisted digestion and the WT correction, the detection limits have improved by a factor of about 5 for Fe, 4 for Mn and Ti, 3 for Si, and 2 for Hf and Na, respectively, in comparison with conventional open-system digestion and off-peak correction. The proposed technique was applied to the analysis of trace elements above-mentioned in three types of ZrO2 powders.
Keywords: Zirconium dioxide; Microwave-assisted digestion; Wavelet transform; Inductively coupled plasma atomic emission spectrometry; Trace element analysis; Spectral interference correction
Development and validation of a new analytical method for the determination of 1,4-dichlorobenzene in honey by gas chromatography–isotope dilution mass spectrometry after steam-distillation by E.V. Botitsi; P.N. Kormali; S.N. Kontou; A. Economou; D.F. Tsipi (pp. 53-60).
A simple, fast, sensitive and robust analytical method using gas chromatography (GC)–isotope dilution mass spectrometry (MS) was developed and validated for the identification and quantification of 1,4-dichlorobenzene ( p-DCB) residues in honey samples. The proposed methodology is based on steam-distillation using a Clevenger-type apparatus followed by gas chromatography–mass spectrometry (GC–MS) in the selected ion monitoring (SIM) mode employing the isotopically labeled analogued4-1,4-dichlorobenzene (d4- p-DCB) as internal standard (IS). Validation of the method was performed in two different GC–MS systems, using quadrupole MS (QMS) and ion-trap MS (ITMS) detectors, with no statistically significant differences between two. Recoveries were better than 91% with percent relative standard deviations lower than 12%. The instrumental limits of detection were 1μgkg−1 in the GC–ITMS system and 0.6μgkg−1 in the GC–QMS system. The expanded uncertainty was estimated as 17% at the currently accepted “action level? of 10μgkg−1. The method was applied to the analysis of 310 honey samples in an extensive national monitoring study. A quality control (QC) system applied during the assays has demonstrated a good performance and long-term stability over a period of more than 8 months of continuous operation.
Keywords: 1,4-Dichlorobenzene; p; -Dichlorobenzene; Honey; Steam-distillation; Gas chromatography; Mass spectrometry; Isotope dilution; Validation
Development and validation of a new analytical method for the determination of 1,4-dichlorobenzene in honey by gas chromatography–isotope dilution mass spectrometry after steam-distillation by E.V. Botitsi; P.N. Kormali; S.N. Kontou; A. Economou; D.F. Tsipi (pp. 53-60).
A simple, fast, sensitive and robust analytical method using gas chromatography (GC)–isotope dilution mass spectrometry (MS) was developed and validated for the identification and quantification of 1,4-dichlorobenzene ( p-DCB) residues in honey samples. The proposed methodology is based on steam-distillation using a Clevenger-type apparatus followed by gas chromatography–mass spectrometry (GC–MS) in the selected ion monitoring (SIM) mode employing the isotopically labeled analogued4-1,4-dichlorobenzene (d4- p-DCB) as internal standard (IS). Validation of the method was performed in two different GC–MS systems, using quadrupole MS (QMS) and ion-trap MS (ITMS) detectors, with no statistically significant differences between two. Recoveries were better than 91% with percent relative standard deviations lower than 12%. The instrumental limits of detection were 1μgkg−1 in the GC–ITMS system and 0.6μgkg−1 in the GC–QMS system. The expanded uncertainty was estimated as 17% at the currently accepted “action level” of 10μgkg−1. The method was applied to the analysis of 310 honey samples in an extensive national monitoring study. A quality control (QC) system applied during the assays has demonstrated a good performance and long-term stability over a period of more than 8 months of continuous operation.
Keywords: 1,4-Dichlorobenzene; p; -Dichlorobenzene; Honey; Steam-distillation; Gas chromatography; Mass spectrometry; Isotope dilution; Validation
Homogeneous chemiluminescent assays for free choline in human plasma and whole blood by Maciej Adamczyk; R. Jeffrey Brashear; Phillip G. Mattingly; Panagiota H. Tsatsos (pp. 61-67).
Choline was oxidized in the presence of choline oxidase and the hydrogen peroxide generated was detected using a chemiluminescent acridinium-9-carboxamide. The dose response for choline (0–150μM) was established in buffer and was validated for the quantification of choline in human plasma and whole blood. This homogeneous assay was performed in a 96-well microplate format and required minimal sample volume (4μL) and short analysis time (<5s per well). The new assay(s) correlated well ( R>0.98, plasma; R>0.97, whole blood) with LC-MS/MS.
Keywords: Chemiluminescence; Choline analysis; Liquid chromatography-electrospray ionization tandem mass spectrometry correlation; Plasma; Whole blood
Homogeneous chemiluminescent assays for free choline in human plasma and whole blood by Maciej Adamczyk; R. Jeffrey Brashear; Phillip G. Mattingly; Panagiota H. Tsatsos (pp. 61-67).
Choline was oxidized in the presence of choline oxidase and the hydrogen peroxide generated was detected using a chemiluminescent acridinium-9-carboxamide. The dose response for choline (0–150μM) was established in buffer and was validated for the quantification of choline in human plasma and whole blood. This homogeneous assay was performed in a 96-well microplate format and required minimal sample volume (4μL) and short analysis time (<5s per well). The new assay(s) correlated well ( R>0.98, plasma; R>0.97, whole blood) with LC-MS/MS.
Keywords: Chemiluminescence; Choline analysis; Liquid chromatography-electrospray ionization tandem mass spectrometry correlation; Plasma; Whole blood
Synthesis of salicylaldehyde-modified mesoporous silica and its application as a new sorbent for separation, preconcentration and determination of uranium by inductively coupled plasma atomic emission spectrometry by Mohammad Reza Jamali; Yaghoub Assadi; Farzaneh Shemirani; Mohammad Reza Milani Hosseini; Reyhaneh Rahnama Kozani; Majid Masteri-Farahani; Masoud Salavati-Niasari (pp. 68-73).
A new functionalized mesoporous silica (MCM-41) using salicylaldehyde was utilized for the separation, preconcentration and determination of uranium in natural water by inductively coupled plasma atomic emission spectrometry (ICP-AES).Experimental conditions for effective adsorption of trace levels of U(VI) were optimized. The preconcentration factor was 100 (1.0mL of elution for a 100mL sample volume). The analytical curve was linear in the range 2–1000μgL−1 and the detection limit was 0.5ngmL−1. The relative standard deviation (R.S.D.) under optimum conditions was 2.5% ( n=10). Common coexisting ions did not interfere with the separation and determination of uranium at pH 5. The sorbent exhibited excellent stability and its sorption capacity under optimum conditions has been found to be 10mg of uranium per gram of sorbent. The method was applied for the recovery and determination of uranium in different water samples.
Keywords: Preconcentration; Determination of uranium; Mesoporous silica; Salicylaldehyde; Inductively coupled plasma atomic emission spectrometry
Synthesis of salicylaldehyde-modified mesoporous silica and its application as a new sorbent for separation, preconcentration and determination of uranium by inductively coupled plasma atomic emission spectrometry by Mohammad Reza Jamali; Yaghoub Assadi; Farzaneh Shemirani; Mohammad Reza Milani Hosseini; Reyhaneh Rahnama Kozani; Majid Masteri-Farahani; Masoud Salavati-Niasari (pp. 68-73).
A new functionalized mesoporous silica (MCM-41) using salicylaldehyde was utilized for the separation, preconcentration and determination of uranium in natural water by inductively coupled plasma atomic emission spectrometry (ICP-AES).Experimental conditions for effective adsorption of trace levels of U(VI) were optimized. The preconcentration factor was 100 (1.0mL of elution for a 100mL sample volume). The analytical curve was linear in the range 2–1000μgL−1 and the detection limit was 0.5ngmL−1. The relative standard deviation (R.S.D.) under optimum conditions was 2.5% ( n=10). Common coexisting ions did not interfere with the separation and determination of uranium at pH 5. The sorbent exhibited excellent stability and its sorption capacity under optimum conditions has been found to be 10mg of uranium per gram of sorbent. The method was applied for the recovery and determination of uranium in different water samples.
Keywords: Preconcentration; Determination of uranium; Mesoporous silica; Salicylaldehyde; Inductively coupled plasma atomic emission spectrometry
Creation of recognition sites for organophosphate esters based on charge transfer and ligand exchange imprinting methods by Rıdvan Say (pp. 74-80).
This manuscript describes a method for the selective binding behavior of paraoxan and parathion compounds on surface imprinted polymers which were prepared using both charge transfer (CT) (methacryloyl-antipyrine, MAAP) and ligand-exchange (LE) (methacryloyl-antipyrine-gadalonium, MAAP-Gd) monomers. These polymers were prepared in the presence of azobisisobutyronitrile (AIBN) as an initiator and crosslinking EDMA and were imprinted with organophosphate esters. Influence of CT and LE imprinting on the creation of recognition sites toward paraoxan and parathion was determined applying adsorption isotherms. The effect of initial concentration of paraoxan and parathion, adsorption time and imprinting efficiency on adsorption selectivity for MIP-CT and MIP-LE was investigated. Association constant ( Kass), number of accessible sites ( Qmax), relative selectivity coefficient ( k′) and binding ability were also evaluated.
Keywords: Organophosphate ester; Molecularly imprinted polymer (MIP); Charge-transfer; Ligand-exchange
Creation of recognition sites for organophosphate esters based on charge transfer and ligand exchange imprinting methods by Rıdvan Say (pp. 74-80).
This manuscript describes a method for the selective binding behavior of paraoxan and parathion compounds on surface imprinted polymers which were prepared using both charge transfer (CT) (methacryloyl-antipyrine, MAAP) and ligand-exchange (LE) (methacryloyl-antipyrine-gadalonium, MAAP-Gd) monomers. These polymers were prepared in the presence of azobisisobutyronitrile (AIBN) as an initiator and crosslinking EDMA and were imprinted with organophosphate esters. Influence of CT and LE imprinting on the creation of recognition sites toward paraoxan and parathion was determined applying adsorption isotherms. The effect of initial concentration of paraoxan and parathion, adsorption time and imprinting efficiency on adsorption selectivity for MIP-CT and MIP-LE was investigated. Association constant ( Kass), number of accessible sites ( Qmax), relative selectivity coefficient ( k′) and binding ability were also evaluated.
Keywords: Organophosphate ester; Molecularly imprinted polymer (MIP); Charge-transfer; Ligand-exchange
Montmorillonite as an adsorbent for extraction and concentration of atrazine, propazine, deethylatrazine, deisopropylatrazine and hydroxyatrazine by Lílian Zarpon; Gilberto Abate; Luciana B.O. dos Santos; Jorge C. Masini (pp. 81-87).
Adsorption properties of the clay mineral montmorillonite in the potassium homoionic form (KMT) was investigated to achieve the extraction and concentration of the herbicides atrazine (AT) and propazine (PROP), as well as the main degradation products of atrazine, namely deethylatrazine (DEA), deisopropylatrazine (DIA) and hydroxyatrazine (ATOH). A batch approach was proposed, with recovery percentages for AT, PROP and DIA higher than 90% at concentrations of 0.50 and 2.50μgL−1. For DEA and ATOH, however, low recoveries were obtained. For DEA, this fact can be explained by its low Kd with KMT, contrary to ATOH, which interacts strongly with the mineral surface, hindering the complete desorption and hence, generating low recovery percentages. The influence of pH, ionic strength and humic acid was studied, and a comparison with the C18 phase as SPE cartridges was carried out. Montmorillonite showed a similar performance to commercial cartridge for concentrations of AT, DEA and PROP, but better recoveries for DIA was obtained using the clay mineral. For ATOH the recovery was also higher on the clay mineral, although for this compound the most suitable SPE cartridge is constituted by cation exchange resin. After the concentration and elution steps, the 0.50 and 2.50μgL−1 gave chromatographic peak areas that could be easily quantified with an analytical curve obtained in the concentration range between 7.5 and 100μgL−1. The obtained concentration factors are suitable to allow the application of the method to the monitoring of triazine residues in drinking water.
Keywords: s; -Triazines; Atrazine metabolites; Montmorillonite; Preconcentration
Montmorillonite as an adsorbent for extraction and concentration of atrazine, propazine, deethylatrazine, deisopropylatrazine and hydroxyatrazine by Lílian Zarpon; Gilberto Abate; Luciana B.O. dos Santos; Jorge C. Masini (pp. 81-87).
Adsorption properties of the clay mineral montmorillonite in the potassium homoionic form (KMT) was investigated to achieve the extraction and concentration of the herbicides atrazine (AT) and propazine (PROP), as well as the main degradation products of atrazine, namely deethylatrazine (DEA), deisopropylatrazine (DIA) and hydroxyatrazine (ATOH). A batch approach was proposed, with recovery percentages for AT, PROP and DIA higher than 90% at concentrations of 0.50 and 2.50μgL−1. For DEA and ATOH, however, low recoveries were obtained. For DEA, this fact can be explained by its low Kd with KMT, contrary to ATOH, which interacts strongly with the mineral surface, hindering the complete desorption and hence, generating low recovery percentages. The influence of pH, ionic strength and humic acid was studied, and a comparison with the C18 phase as SPE cartridges was carried out. Montmorillonite showed a similar performance to commercial cartridge for concentrations of AT, DEA and PROP, but better recoveries for DIA was obtained using the clay mineral. For ATOH the recovery was also higher on the clay mineral, although for this compound the most suitable SPE cartridge is constituted by cation exchange resin. After the concentration and elution steps, the 0.50 and 2.50μgL−1 gave chromatographic peak areas that could be easily quantified with an analytical curve obtained in the concentration range between 7.5 and 100μgL−1. The obtained concentration factors are suitable to allow the application of the method to the monitoring of triazine residues in drinking water.
Keywords: s; -Triazines; Atrazine metabolites; Montmorillonite; Preconcentration
Optimization of microwave-assisted solvent extraction for volatile organic acids in tobacco and its comparison with conventional extraction methods by Xiaolan Zhu; Qingde Su; Jibao Cai; Jun Yang (pp. 88-94).
In the present study, a new method using microwave-assisted solvent extraction (MASE) technique followed directly GC analysis was developed for the extraction of volatile organic acids (VOAs) in tobacco. The MASE conditions (heating time, volume of extracting solvent and extraction temperature) were optimized by means of an orthogonal array design (OAD) procedure. The results suggested that extractant, temperature and heating time were statistically the most significant factors. The extracts were directly analyzed with capillary GC operating in splitless-injection mode on an Agilent HP-FFAP capillary column. Under optimum operating conditions, MASE showed significantly better recoveries than those obtained by the conventional extraction method (ultrasonic and reflux extraction), ranging from 90.6% to 103.2%. In addition, a drastic reduction of the extraction time (20min versus 4h) and solvent consumption (20mL versus 100mL) was achieved with an outstanding reproducibility (CV ≤5%).
Keywords: Volatile organic acids; Tobacco; Microwave-assisted solvent extraction; Orthogonal array design; Gas chromatography
Optimization of microwave-assisted solvent extraction for volatile organic acids in tobacco and its comparison with conventional extraction methods by Xiaolan Zhu; Qingde Su; Jibao Cai; Jun Yang (pp. 88-94).
In the present study, a new method using microwave-assisted solvent extraction (MASE) technique followed directly GC analysis was developed for the extraction of volatile organic acids (VOAs) in tobacco. The MASE conditions (heating time, volume of extracting solvent and extraction temperature) were optimized by means of an orthogonal array design (OAD) procedure. The results suggested that extractant, temperature and heating time were statistically the most significant factors. The extracts were directly analyzed with capillary GC operating in splitless-injection mode on an Agilent HP-FFAP capillary column. Under optimum operating conditions, MASE showed significantly better recoveries than those obtained by the conventional extraction method (ultrasonic and reflux extraction), ranging from 90.6% to 103.2%. In addition, a drastic reduction of the extraction time (20min versus 4h) and solvent consumption (20mL versus 100mL) was achieved with an outstanding reproducibility (CV ≤5%).
Keywords: Volatile organic acids; Tobacco; Microwave-assisted solvent extraction; Orthogonal array design; Gas chromatography
Monitoring of bentonite pore water with a probe based on solid-state microsensors by Jahir Orozco; Antoni Baldi; Pedro L. Martín; Andrei Bratov; Cecilia Jiménez (pp. 95-101).
Repositories for the disposal of radioactive waste generally rely on a multi-barrier system to isolate the waste from the biosphere. This multi-barrier system typically comprises the natural geological barrier provided by the repository host rock and its surroundings and an engineered barrier system (EBS). Bentonite is being studied as an appropriated porous material for an EBS to prevent or delay the release and transport of radionuclides towards biosphere. The study of pore water chemistry within bentonite barriers will permit to understand the transport phenomena of radionuclides and obtain a database of the bentonite-water interaction processes. In this work, the measurement of some chemical parameters in bentonite pore water using solid-state microsensors is proposed. Those sensors are well suited for this application since in situ measurements are feasible and they are robust enough for the long periods of time that monitoring is needed in an EBS. A probe containing an ISFET (ion sensitive field effect transistor) for measuring pH, and platinum microelectrodes for measuring conductivity and redox potential was developed, together with the required instrumentation, to study the chemical changes in a test cell with compacted bentonite. Response features of the sensors’ probe and instrumentation performance in synthetic samples with compositions similar to those present in bentonite barriers are reported. Measurements of sensors stability in a test cell are also presented.
Keywords: Pore water monitoring; pH ion sensitive field effect transistor; Platinum microelectrodes; Redox potential; Conductivity; Bentonite
Monitoring of bentonite pore water with a probe based on solid-state microsensors by Jahir Orozco; Antoni Baldi; Pedro L. Martín; Andrei Bratov; Cecilia Jiménez (pp. 95-101).
Repositories for the disposal of radioactive waste generally rely on a multi-barrier system to isolate the waste from the biosphere. This multi-barrier system typically comprises the natural geological barrier provided by the repository host rock and its surroundings and an engineered barrier system (EBS). Bentonite is being studied as an appropriated porous material for an EBS to prevent or delay the release and transport of radionuclides towards biosphere. The study of pore water chemistry within bentonite barriers will permit to understand the transport phenomena of radionuclides and obtain a database of the bentonite-water interaction processes. In this work, the measurement of some chemical parameters in bentonite pore water using solid-state microsensors is proposed. Those sensors are well suited for this application since in situ measurements are feasible and they are robust enough for the long periods of time that monitoring is needed in an EBS. A probe containing an ISFET (ion sensitive field effect transistor) for measuring pH, and platinum microelectrodes for measuring conductivity and redox potential was developed, together with the required instrumentation, to study the chemical changes in a test cell with compacted bentonite. Response features of the sensors’ probe and instrumentation performance in synthetic samples with compositions similar to those present in bentonite barriers are reported. Measurements of sensors stability in a test cell are also presented.
Keywords: Pore water monitoring; pH ion sensitive field effect transistor; Platinum microelectrodes; Redox potential; Conductivity; Bentonite
Potentiometric membrane sensor based on 6-(4-nitrophenyl)-2,4-diphenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene for detection of Sn(II) in real samples by Majid Arvand; A. Majid Moghimi; Anoosheh Afshari; Nosratollah Mahmoodi (pp. 102-108).
A Sn2+ ion-selective electrode which was prepared with a polymeric membrane based on 6-(4-nitrophenyl)-2,4-diphenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene (NDDBH) as a ionophore. Effects of experimental parameters such as membrane composition, nature and amount of plasticizer, the amount of additive and concentration of internal solution on the potential response of Sn2+ sensor were investigated. The electrode exhibited a Nernstian slope of 28.8±1.1mV/decade of Sn2+ over a concentration range of 1.0×10−5 to 1.0×10−1M of Sn2+ in an acidic solution (pH 1). The limit of detection was 4.0×10−6M. The results show that this electrode can be used in ethanol media until 20% (v/v) concentration without interference. It can be used for more than 6 weeks without any considerable divergence in the potentials. The proposed membrane electrode revealed very good selectivity for Sn(II) ions over a wide variety of other cations and could be used in acidic media. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode. The stability constant (log Ks) of the Sn(II)–ionophore complex was determined at 25°C by potentiometric titration in mixed aqueous solution. It was used as indicator electrode in potentiometric determination of Sn(II) ion in real samples.
Keywords: Potentiometric Sn(II) sensor; Poly(vinyl chloride) membrane; Non-aqueous media; Isothermal temperature coefficient
Potentiometric membrane sensor based on 6-(4-nitrophenyl)-2,4-diphenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene for detection of Sn(II) in real samples by Majid Arvand; A. Majid Moghimi; Anoosheh Afshari; Nosratollah Mahmoodi (pp. 102-108).
A Sn2+ ion-selective electrode which was prepared with a polymeric membrane based on 6-(4-nitrophenyl)-2,4-diphenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene (NDDBH) as a ionophore. Effects of experimental parameters such as membrane composition, nature and amount of plasticizer, the amount of additive and concentration of internal solution on the potential response of Sn2+ sensor were investigated. The electrode exhibited a Nernstian slope of 28.8±1.1mV/decade of Sn2+ over a concentration range of 1.0×10−5 to 1.0×10−1M of Sn2+ in an acidic solution (pH 1). The limit of detection was 4.0×10−6M. The results show that this electrode can be used in ethanol media until 20% (v/v) concentration without interference. It can be used for more than 6 weeks without any considerable divergence in the potentials. The proposed membrane electrode revealed very good selectivity for Sn(II) ions over a wide variety of other cations and could be used in acidic media. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode. The stability constant (log Ks) of the Sn(II)–ionophore complex was determined at 25°C by potentiometric titration in mixed aqueous solution. It was used as indicator electrode in potentiometric determination of Sn(II) ion in real samples.
Keywords: Potentiometric Sn(II) sensor; Poly(vinyl chloride) membrane; Non-aqueous media; Isothermal temperature coefficient
Simultaneous amperometric determination of lignin peroxidase and manganese peroxidase activities in compost bioremediation using artificial neural networks by Lin Tang; Guang-Ming Zeng; Guo-Li Shen; Yi Zhang; Guo-He Huang; Jian-Bing Li (pp. 109-116).
The activities of lignin-degrading peroxidases are the primary decomposition indexes in compost bioremediation. In this paper, artificial neural networks (ANNs) have been combined with an enzyme sensor for simultaneous determination of lignin peroxidase (LiP) and manganese peroxidase (MnP) activities secreted by Phanerochaete chrysosporium in composting of municipal solid waste. The LiP and MnP activities were detected through catalytic redox of H2O2, hydroquinone and veratryl alcohol as substrates by an amperometric sensor immersed in the culture filtrate solution. Due to the dynamic, nonlinear and uncertain characteristics of the complex composting system, ANNs have been used as a chemometric tool for overlapping signal deconvolution and modelling to quantify the two enzyme activities separately. Feedforward backpropagation network was used for the training process. The effects of the transfer functions, the amount of current values, the number of hidden neurons and the optimization algorithm were investigated. The LiP activities in the filtrate varied from 8.14 to 29.79UL−1, and from 0.36 to 1.37UL−1 for MnP activities. A good prediction capability was obtained, with correlation coefficients of 0.9936 for LiP activity and 0.9976 for MnP activity between the expected and predicted values of the external test samples. The performance of the ANN model was compared with the linear regression model in respect to simulation accuracy, adaptability to uncertainty, etc. All the results show that the combination of amperometric enzyme sensor and artificial neural networks is a rapid, sensitive and robust method in the quantitative study of composting system.
Keywords: Amperometric determination; Lignin peroxidase; Manganese peroxidase; Enzyme activity; Artificial neural networks; Compost bioremediation
Simultaneous amperometric determination of lignin peroxidase and manganese peroxidase activities in compost bioremediation using artificial neural networks by Lin Tang; Guang-Ming Zeng; Guo-Li Shen; Yi Zhang; Guo-He Huang; Jian-Bing Li (pp. 109-116).
The activities of lignin-degrading peroxidases are the primary decomposition indexes in compost bioremediation. In this paper, artificial neural networks (ANNs) have been combined with an enzyme sensor for simultaneous determination of lignin peroxidase (LiP) and manganese peroxidase (MnP) activities secreted by Phanerochaete chrysosporium in composting of municipal solid waste. The LiP and MnP activities were detected through catalytic redox of H2O2, hydroquinone and veratryl alcohol as substrates by an amperometric sensor immersed in the culture filtrate solution. Due to the dynamic, nonlinear and uncertain characteristics of the complex composting system, ANNs have been used as a chemometric tool for overlapping signal deconvolution and modelling to quantify the two enzyme activities separately. Feedforward backpropagation network was used for the training process. The effects of the transfer functions, the amount of current values, the number of hidden neurons and the optimization algorithm were investigated. The LiP activities in the filtrate varied from 8.14 to 29.79UL−1, and from 0.36 to 1.37UL−1 for MnP activities. A good prediction capability was obtained, with correlation coefficients of 0.9936 for LiP activity and 0.9976 for MnP activity between the expected and predicted values of the external test samples. The performance of the ANN model was compared with the linear regression model in respect to simulation accuracy, adaptability to uncertainty, etc. All the results show that the combination of amperometric enzyme sensor and artificial neural networks is a rapid, sensitive and robust method in the quantitative study of composting system.
Keywords: Amperometric determination; Lignin peroxidase; Manganese peroxidase; Enzyme activity; Artificial neural networks; Compost bioremediation
Determination of triflumizole by differential pulse polarography in formulation, soil and natural water samples by Recai İnam; Ebru Zeynep Gülerman; Tuba Sarıgül (pp. 117-123).
A novel electroanalytical procedure is proposed for the determination of the triflumizole in formulation, soil and natural water samples using differential pulse polarography (DPP). Triflumizole exhibited a single well-defined cathodic peak over the pH range of 1.0–9.0 in Britton–Robinson (B–R) buffers. The peak potentials were shifted to more negative values upon increasing the pH and a plot of reduction potentials ( Ep) versus pH exhibited two linear segments with a break at pH 4.0 which corresponded to the pKa±1 value of triflumizole. The peak appeared as a maximum at pH 2.0 (−810mV versus saturated calomel electrode (SCE)) was well resolved and suitable to be investigated for analytical use. The current–concentration plot obtained using this peak was rectilinear over the range from 2.0 to 91.0μmolL−1 with a correlation coefficient of 0.993. The limit of detection (LOD) and limit of quantification (LOQ) were obtained as 0.72 and 2.39μmolL−1, respectively. The proposed method was successfully applied to the determination of triflumizole in spiked soil and lake water. The mean recoveries of the pesticide were 102.1 and 103.6% with a relative standard deviation of 1.01 and 2.68% in soil and lake water, respectively. The method was extended to the determination of triflumizole in agrochemical fungicide formulation Trifmine® and results were in agreement with that obtained by high-performance liquid chromatographic analysis (HPLC). The influence of some diverse ions and some other pesticides was also investigated.
Keywords: Polarography; Determination; Pesticide; Triflumizole
Determination of triflumizole by differential pulse polarography in formulation, soil and natural water samples by Recai İnam; Ebru Zeynep Gülerman; Tuba Sarıgül (pp. 117-123).
A novel electroanalytical procedure is proposed for the determination of the triflumizole in formulation, soil and natural water samples using differential pulse polarography (DPP). Triflumizole exhibited a single well-defined cathodic peak over the pH range of 1.0–9.0 in Britton–Robinson (B–R) buffers. The peak potentials were shifted to more negative values upon increasing the pH and a plot of reduction potentials ( Ep) versus pH exhibited two linear segments with a break at pH 4.0 which corresponded to the pKa±1 value of triflumizole. The peak appeared as a maximum at pH 2.0 (−810mV versus saturated calomel electrode (SCE)) was well resolved and suitable to be investigated for analytical use. The current–concentration plot obtained using this peak was rectilinear over the range from 2.0 to 91.0μmolL−1 with a correlation coefficient of 0.993. The limit of detection (LOD) and limit of quantification (LOQ) were obtained as 0.72 and 2.39μmolL−1, respectively. The proposed method was successfully applied to the determination of triflumizole in spiked soil and lake water. The mean recoveries of the pesticide were 102.1 and 103.6% with a relative standard deviation of 1.01 and 2.68% in soil and lake water, respectively. The method was extended to the determination of triflumizole in agrochemical fungicide formulation Trifmine® and results were in agreement with that obtained by high-performance liquid chromatographic analysis (HPLC). The influence of some diverse ions and some other pesticides was also investigated.
Keywords: Polarography; Determination; Pesticide; Triflumizole