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Stir bar sorptive extraction coupled to liquid chromatography-tandem mass spectrometry for the determination of pesticides in water samples: Method validation and measurement uncertainty
08 July 2013,
08:51:54
Publication date: 15 November
2013
Source:Talanta, Volume 116
Author(s): Christelle Margoum , Céline Guillemain , Xi Yang , Marina Coquery
Stir bar sorptive extraction followed by liquid desorption and high performance liquid chromatography with tandem mass spectrometry (SBSE-LD-LC-MSMS) has been developed for the determination of 15 pesticides or selected metabolites from different families (herbicides, insecticides, fungicides) in surface water samples. The optimization of parameters that could influence SBSE-LD efficiency was carried out by means of experimental design. Optimized conditions were established as follows concerning extraction time, stirring speed, aqueous medium characteristics (ionic strength and polarity) and back desorption solvent and time, respectively: 3h (800rpm), addition of 10% of sodium chloride, no addition of methanol as organic modifier, and 15min ultrasonic desorption in equivolume mixtures of acetonitrile-methanol. A specific and thorough cleanup procedure was developed and applied to each stir bar to avoid possible carry-over between consecutive extractions with the same stir bar. Pesticide quantification in water was achieved thanks to matrix matched calibration. Mean recoveries ranged from 93 to 101% (RSD <17%, n=30). Validated limits of quantification in matrix were between 0.02 and 1µgL−1, depending on the compound. A specific experimental design was conducted to evaluate the measurement uncertainty, which was comprised between 13 and 51%, whatever the pesticide and the concentration level. The applicability of the SBSE-LD-LCMSMS method was evaluated by analyzing surface water samples and by comparing with conventional solid phase extraction-LC-MSMS procedure.
Source:Talanta, Volume 116
Author(s): Christelle Margoum , Céline Guillemain , Xi Yang , Marina Coquery
Stir bar sorptive extraction followed by liquid desorption and high performance liquid chromatography with tandem mass spectrometry (SBSE-LD-LC-MSMS) has been developed for the determination of 15 pesticides or selected metabolites from different families (herbicides, insecticides, fungicides) in surface water samples. The optimization of parameters that could influence SBSE-LD efficiency was carried out by means of experimental design. Optimized conditions were established as follows concerning extraction time, stirring speed, aqueous medium characteristics (ionic strength and polarity) and back desorption solvent and time, respectively: 3h (800rpm), addition of 10% of sodium chloride, no addition of methanol as organic modifier, and 15min ultrasonic desorption in equivolume mixtures of acetonitrile-methanol. A specific and thorough cleanup procedure was developed and applied to each stir bar to avoid possible carry-over between consecutive extractions with the same stir bar. Pesticide quantification in water was achieved thanks to matrix matched calibration. Mean recoveries ranged from 93 to 101% (RSD <17%, n=30). Validated limits of quantification in matrix were between 0.02 and 1µgL−1, depending on the compound. A specific experimental design was conducted to evaluate the measurement uncertainty, which was comprised between 13 and 51%, whatever the pesticide and the concentration level. The applicability of the SBSE-LD-LCMSMS method was evaluated by analyzing surface water samples and by comparing with conventional solid phase extraction-LC-MSMS procedure.
Graphical abstract
Investigating of labelling and detection of transthyretin synthetic peptide derivatized with naphthalene-2,3-dicarboxaldehyde
08 July 2013,
08:51:54
Publication date: 15 November
2013
Source:Talanta, Volume 116
Author(s): Mathilde Faure , Sonia Korchane , Isabelle Le Potier , Antoine Pallandre , Claude Deslouis , Anne-Marie Haghiri-Gosnet , Jean Gamby
Labelling and detection of a synthetic peptide (PN) mimicking a tryptic fragment of interest for the diagnosis of familial amyloidal polyneuropathy have been investigated optically and electrochemically. We decided to covalently label naphtalene-2,3-dicarboxyaldehyde (NDA), a fluorogenic and electroactive molecule on PN. First, the optimization of the labelling chemical reaction was performed by capillary electrophoresis coupled with laser induced fluorescence detection (CE-LIF). The analytical parameters such as separation efficiency and peak area were considered to propose this optimized derivatization reaction. The results obtained allowed us to establish the pH and ionic strength of the derivatization buffer, the molar ratio between NDA and PN and the reaction time of the labelling. Optimal conditions are obtained when [NDA]/[PN]=40, buffer pH of 9, buffer ionic strength of 70mM and reaction time of 15min. Second, differential pulse voltammetry (DPV) and cyclic voltammetry (CV) were also used to characterize NDA-labelled PN and different electroinactive amino acids (histidine, lysine, serine, threonine) which are in the PN sequence. The electrochemical detection experiments demonstrated that the labelled biomolecules could be also easily detected at low concentration. Moreover, the derivatization reaction could be followed to describe more precisely the labelling process of these biomolecules. Optimal conditions for labelling are obtained when [NDA]total/[CN-] ratio =1 and [NDA]total/[amino acid or peptide]=100 with a buffer having a pH=9 on a glassy carbon electrode. In all cases, an obvious oxidation peak for the N-2-substituted-1-cyanobenz-[f]-isoindole derivative (CBI) has been observed at 0.5–0.7V/SCE. The multi-labelling of PN and lysine were shown with DPV. We presumed this result to occur because of the shouldered shape of the DPV peak shape. These experiments confirm that NDA can be used as a derivative agent for PN, allowing for electrochemical and fluorescence detections with a limit of detection of labelled PN estimated at 0.2µM and 5µM, respectively.
Source:Talanta, Volume 116
Author(s): Mathilde Faure , Sonia Korchane , Isabelle Le Potier , Antoine Pallandre , Claude Deslouis , Anne-Marie Haghiri-Gosnet , Jean Gamby
Labelling and detection of a synthetic peptide (PN) mimicking a tryptic fragment of interest for the diagnosis of familial amyloidal polyneuropathy have been investigated optically and electrochemically. We decided to covalently label naphtalene-2,3-dicarboxyaldehyde (NDA), a fluorogenic and electroactive molecule on PN. First, the optimization of the labelling chemical reaction was performed by capillary electrophoresis coupled with laser induced fluorescence detection (CE-LIF). The analytical parameters such as separation efficiency and peak area were considered to propose this optimized derivatization reaction. The results obtained allowed us to establish the pH and ionic strength of the derivatization buffer, the molar ratio between NDA and PN and the reaction time of the labelling. Optimal conditions are obtained when [NDA]/[PN]=40, buffer pH of 9, buffer ionic strength of 70mM and reaction time of 15min. Second, differential pulse voltammetry (DPV) and cyclic voltammetry (CV) were also used to characterize NDA-labelled PN and different electroinactive amino acids (histidine, lysine, serine, threonine) which are in the PN sequence. The electrochemical detection experiments demonstrated that the labelled biomolecules could be also easily detected at low concentration. Moreover, the derivatization reaction could be followed to describe more precisely the labelling process of these biomolecules. Optimal conditions for labelling are obtained when [NDA]total/[CN-] ratio =1 and [NDA]total/[amino acid or peptide]=100 with a buffer having a pH=9 on a glassy carbon electrode. In all cases, an obvious oxidation peak for the N-2-substituted-1-cyanobenz-[f]-isoindole derivative (CBI) has been observed at 0.5–0.7V/SCE. The multi-labelling of PN and lysine were shown with DPV. We presumed this result to occur because of the shouldered shape of the DPV peak shape. These experiments confirm that NDA can be used as a derivative agent for PN, allowing for electrochemical and fluorescence detections with a limit of detection of labelled PN estimated at 0.2µM and 5µM, respectively.
Surface-enhanced Raman spectroscopy detection of polybrominated diphenylethers using a portable Raman spectrometer
08 July 2013,
08:51:54
Publication date: 15 November
2013
Source:Talanta, Volume 116
Author(s): Xiaohong Jiang , Yongchao Lai , Wei Wang , Wei Jiang , Jinhua Zhan
Polybrominated diphenylethers (PBDEs), one of the most common brominated flame retardants, are toxic and persistent, generally detected by the chromatographic method. In this work, qualitative and quantitative detection of PBDEs were explored based on surface-enhanced Raman spectroscopy (SERS) technique using a portable Raman spectrometer. Alkanethiol modified silver nanoparticle aggregates were used as the substrate and PBDEs could be pre-concentrated close to the substrate surface through their hydrophobic interactions with alkanethiol. The effect of alkanethiols with different chain length on the SERS detection of PBDEs was evaluated. It was shown that 1-hexanethiol (HT) modified substrate has higher sensitivity, good stability and reusability. Qualitative and quantitative SERS detection of PBDEs in real sea water was accomplished, with the measured detection limits at 1.2×102 μgL−1. These results illustrate SERS could be used as an effective method for the detection of PBDEs.
Source:Talanta, Volume 116
Author(s): Xiaohong Jiang , Yongchao Lai , Wei Wang , Wei Jiang , Jinhua Zhan
Polybrominated diphenylethers (PBDEs), one of the most common brominated flame retardants, are toxic and persistent, generally detected by the chromatographic method. In this work, qualitative and quantitative detection of PBDEs were explored based on surface-enhanced Raman spectroscopy (SERS) technique using a portable Raman spectrometer. Alkanethiol modified silver nanoparticle aggregates were used as the substrate and PBDEs could be pre-concentrated close to the substrate surface through their hydrophobic interactions with alkanethiol. The effect of alkanethiols with different chain length on the SERS detection of PBDEs was evaluated. It was shown that 1-hexanethiol (HT) modified substrate has higher sensitivity, good stability and reusability. Qualitative and quantitative SERS detection of PBDEs in real sea water was accomplished, with the measured detection limits at 1.2×102 μgL−1. These results illustrate SERS could be used as an effective method for the detection of PBDEs.
Determination of trace level cadmium in SRM 3280 Multivitamin/Multielement Tablets via isotope dilution inductively coupled plasma mass spectrometry
08 July 2013,
08:51:54
Publication date: 15 November
2013
Source:Talanta, Volume 116
Author(s): Steven J. Christopher , Robert Q. Thompson
Cadmium was quantified at 80.15±0.86ng/g (mean±95% expanded uncertainty) in NIST SRM 3280 Multivitamin/Multielement Tablets, using isotope dilution mass spectrometry. The method described utilized various precipitation and solid-phase extraction separation methodologies to isolate Cd from Sn and Mo, present respectively, at 11.1±0.9mg/kg and 70.7±4.5mg/kg in the tablet matrix. This allowed for measurement of 111Cd/113Cd and 111Cd/114Cd isotope ratios using both quadrupole collision cell technology inductively coupled plasma mass spectrometry (Q-CCT-ICP-MS) and sector field (SF)-ICP-MS equipped with a desolvating nebulizer system to mitigate the MoO+ and MoOH+ molecular ion interferences that typically affect the envelope of Cd isotopes.
Source:Talanta, Volume 116
Author(s): Steven J. Christopher , Robert Q. Thompson
Cadmium was quantified at 80.15±0.86ng/g (mean±95% expanded uncertainty) in NIST SRM 3280 Multivitamin/Multielement Tablets, using isotope dilution mass spectrometry. The method described utilized various precipitation and solid-phase extraction separation methodologies to isolate Cd from Sn and Mo, present respectively, at 11.1±0.9mg/kg and 70.7±4.5mg/kg in the tablet matrix. This allowed for measurement of 111Cd/113Cd and 111Cd/114Cd isotope ratios using both quadrupole collision cell technology inductively coupled plasma mass spectrometry (Q-CCT-ICP-MS) and sector field (SF)-ICP-MS equipped with a desolvating nebulizer system to mitigate the MoO+ and MoOH+ molecular ion interferences that typically affect the envelope of Cd isotopes.
On-chip electrochemical microsystems for measurements of copper and conductivity in artificial seawater
08 July 2013,
08:51:54
Publication date: 15 November
2013
Source:Talanta, Volume 116
Author(s): Grégoire Herzog , Waleed Moujahid , Karen Twomey , Conor Lyons , Vladimir I. Ogurtsov
The fabrication and characterisation of microelectrochemical sensors for Cu2+ and conductivity suitable for operation in the marine environment are presented. The impact of the designs on sensor performance and their adequacy to operate in real conditions are discussed. The sensors, tailored to voltammetric and impedimetric measurements, are fabricated on silicon using photolithographic and thin film deposition techniques. The impedimetric sensor is made of Pt interdigitated electrodes which are used for the measurement of conductivity. The voltammetric sensors are based on a three electrode electrochemical cell with on-chip Ag|AgCl reference and Pt counter and working electrodes, used for detection of copper by underpotential deposition-stripping voltammetry at microelectrode array. The sensors operated in the Cu2+ concentrations ranging from 0.48 to 3.97µM with a limit of detection of 0.115μM. The impact of the temperature, the pH and the salinity of the artificial seawater on the sensitivity for Cu2+ detection are also considered. Measurements of copper concentration and conductivity are validated using certified reference materials and standard solutions.
Source:Talanta, Volume 116
Author(s): Grégoire Herzog , Waleed Moujahid , Karen Twomey , Conor Lyons , Vladimir I. Ogurtsov
The fabrication and characterisation of microelectrochemical sensors for Cu2+ and conductivity suitable for operation in the marine environment are presented. The impact of the designs on sensor performance and their adequacy to operate in real conditions are discussed. The sensors, tailored to voltammetric and impedimetric measurements, are fabricated on silicon using photolithographic and thin film deposition techniques. The impedimetric sensor is made of Pt interdigitated electrodes which are used for the measurement of conductivity. The voltammetric sensors are based on a three electrode electrochemical cell with on-chip Ag|AgCl reference and Pt counter and working electrodes, used for detection of copper by underpotential deposition-stripping voltammetry at microelectrode array. The sensors operated in the Cu2+ concentrations ranging from 0.48 to 3.97µM with a limit of detection of 0.115μM. The impact of the temperature, the pH and the salinity of the artificial seawater on the sensitivity for Cu2+ detection are also considered. Measurements of copper concentration and conductivity are validated using certified reference materials and standard solutions.
Detection of chemical residues in tangerine juices by a duplex immunoassay
08 July 2013,
08:51:54
Publication date: 15 November
2013
Source:Talanta, Volume 116
Author(s): P. Navarro , A.J. Pérez , J.A. Gabaldón , E. Núñez-Delicado , R. Puchades , A. Maquieira , S. Morais
A rapid duplex ELISA for the simultaneous determination of two of the most widely used organophosphorous insecticides in tangerine juices is described. To accomplish this aim, two individual enzyme-linked immunosorbent assays for chlorpyrifos and fenthion pesticides were integrated into one ELISA test. The strategy uses 96-well plates with specific wells coated with the corresponding haptenized conjugate. The optimized duplex ELISA was accomplished within 40min achieving a detection limit of 0.20±0.04µg/L and 0.50±0.06µg/L, for chlorpyrifos and fenthion, respectively in tangerine juice samples. The determination of residues of both pesticides was carried out by simple sample dilution, without any extra sample clean-up procedure. Results of testing precision, stability, and selectivity demonstrated that the assay provided reliable analytical performances for the simultaneous determination of residues of chlorpyrifos and fenthion in fruit juice samples below the established European maximum residue limits (MRL). In addition, the accuracy and reliability of this duplex bioanalytical method is demonstrated by analyzing blind spiked juice samples and the results, correlated well with those achieved using a well-established GC/MS method (recoveries between 95% and 106%).
Source:Talanta, Volume 116
Author(s): P. Navarro , A.J. Pérez , J.A. Gabaldón , E. Núñez-Delicado , R. Puchades , A. Maquieira , S. Morais
A rapid duplex ELISA for the simultaneous determination of two of the most widely used organophosphorous insecticides in tangerine juices is described. To accomplish this aim, two individual enzyme-linked immunosorbent assays for chlorpyrifos and fenthion pesticides were integrated into one ELISA test. The strategy uses 96-well plates with specific wells coated with the corresponding haptenized conjugate. The optimized duplex ELISA was accomplished within 40min achieving a detection limit of 0.20±0.04µg/L and 0.50±0.06µg/L, for chlorpyrifos and fenthion, respectively in tangerine juice samples. The determination of residues of both pesticides was carried out by simple sample dilution, without any extra sample clean-up procedure. Results of testing precision, stability, and selectivity demonstrated that the assay provided reliable analytical performances for the simultaneous determination of residues of chlorpyrifos and fenthion in fruit juice samples below the established European maximum residue limits (MRL). In addition, the accuracy and reliability of this duplex bioanalytical method is demonstrated by analyzing blind spiked juice samples and the results, correlated well with those achieved using a well-established GC/MS method (recoveries between 95% and 106%).
Graphical abstract
Semiautomated solid-phase extraction manifold with a solvent-level sensor
08 July 2013,
08:51:54
Publication date: 15 November
2013
Source:Talanta, Volume 116
Author(s): R.M. Orlando , S. Rath , J.J.R. Rohwedder
A semiautomated solid-phase extraction manifold for multiple extractions is presented. The manifold utilizes commercial solid-phase syringe cartridges and automatically introduces and elutes all the solvents during the extraction, reducing the typical workload and stress of the analyst. The manifold consists of a peristaltic pump with solenoid valves in a flow circuit that contains transmissive photomicrosensors. The photomicrosensors were used to control the solvent dispenser and the solvent level inside the cartridge. As solvent-level sensors, the photomicrosensors determined the exact time the solvent reached the top frit to avoid sorbent drying and accurately perform the solvent exchange. The repeatability of the manifold to introduce a particular volume of solvent into the cartridges was measured, and the precisions were between 0.05 and 2.89% (RSD). To evaluate the manifold, the amount of two fluoroquinolones in a fortified blank milk sample was determined. The results of the intra- and inter-day precision of multiple extractions from the fortified milk samples resulted in precisions better than 9.0% (RSD) and confirmed that the arrangement of the semiautomated manifold could adequately be used in solid-phase extraction with commercial cartridges.
Source:Talanta, Volume 116
Author(s): R.M. Orlando , S. Rath , J.J.R. Rohwedder
A semiautomated solid-phase extraction manifold for multiple extractions is presented. The manifold utilizes commercial solid-phase syringe cartridges and automatically introduces and elutes all the solvents during the extraction, reducing the typical workload and stress of the analyst. The manifold consists of a peristaltic pump with solenoid valves in a flow circuit that contains transmissive photomicrosensors. The photomicrosensors were used to control the solvent dispenser and the solvent level inside the cartridge. As solvent-level sensors, the photomicrosensors determined the exact time the solvent reached the top frit to avoid sorbent drying and accurately perform the solvent exchange. The repeatability of the manifold to introduce a particular volume of solvent into the cartridges was measured, and the precisions were between 0.05 and 2.89% (RSD). To evaluate the manifold, the amount of two fluoroquinolones in a fortified blank milk sample was determined. The results of the intra- and inter-day precision of multiple extractions from the fortified milk samples resulted in precisions better than 9.0% (RSD) and confirmed that the arrangement of the semiautomated manifold could adequately be used in solid-phase extraction with commercial cartridges.
The connection between inverse and classical calibration
08 July 2013,
08:51:54
Publication date: 15 November
2013
Source:Talanta, Volume 116
Author(s): Emili Besalú
Within the context of the simple classical linear calibration procedure (regression of y on x), here it is shown how a distinction between the distributions of the observed dependent variable (y obs ) and the calculated (fitted) one (y calc ) leads to the following counterintuitive approach: in order to get the independent x values with lesser systematic deviations, do not identify as direct inputs in the classical calibration equation the new y observed ones (experimentally acquired), but instead the transformed ones by means of a regression towards the mean effect correction. It is shown how the conjunction of both steps, i.e., first the transformation of observed values and then the ulterior use in the classical calibration equation, corresponds to an operation totally equivalent to the direct implementation of the inverse calibration equation (regression of x on y in a single step). The reasoning given here explains in a simple manner why the inverse calibration numerically performs usually better for predictions of interpolated x values. Results are accompanied with the analysis of both theoretical and experimental data.
Source:Talanta, Volume 116
Author(s): Emili Besalú
Within the context of the simple classical linear calibration procedure (regression of y on x), here it is shown how a distinction between the distributions of the observed dependent variable (y obs ) and the calculated (fitted) one (y calc ) leads to the following counterintuitive approach: in order to get the independent x values with lesser systematic deviations, do not identify as direct inputs in the classical calibration equation the new y observed ones (experimentally acquired), but instead the transformed ones by means of a regression towards the mean effect correction. It is shown how the conjunction of both steps, i.e., first the transformation of observed values and then the ulterior use in the classical calibration equation, corresponds to an operation totally equivalent to the direct implementation of the inverse calibration equation (regression of x on y in a single step). The reasoning given here explains in a simple manner why the inverse calibration numerically performs usually better for predictions of interpolated x values. Results are accompanied with the analysis of both theoretical and experimental data.
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