The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Víctor Cerdà - One of the best experts on this subject based on the ideXlab platform.
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Simultaneous determination of fluorophores with overlapped spectra by sequential injection analysis coupled to variable angle scanning fluorescence spectrometry and multivariate linear regression algorithms
Analytica Chimica Acta, 2002Co-Authors: G De Armas, J.m. Estela, Manuel Miró, Víctor CerdàAbstract:Abstract An automated and versatile sequential injection spectrofluorimetric procedure for the simultaneous determination of multicomponent mixtures in micellar medium without prior separation processes is reported. The methodology is based upon the segmentation of a sample slug between two different buffer zones in order to attain both an improvement of sensitivity and residual minimization for the whole species. Resolution of overlapping fluorescence profiles is achieved using a variable angle scanning technique coupled to multivariate least-squares regression (MLR) algorithms at both sample edges. The potentialities of the described methodology are illustrated with the spectrofluorimetric determination of four widespread pesticides with different acid–base properties; viz. carbaryl (CBL) (1-naphthyl- N -methylcarbamate), Fuberidazole (FBZ) (2-(2′-furyl)benzimidazole), thiabendazole (TBZ) (2-(4′-thiazolyl)benzimidazole) and warfarin (W) (3-α-acetonylbenzyl)-4-hydroxycoumarin). Detection limits at the 3 σ level were 3.9, 0.02, 0.03 and 10 μg l −1 for CBL, FBZ, TBZ and W, respectively at the maximum sensitivity pH. Dynamic ranges of 13–720 μg l −1 CBL, 0.10–14 μg l −1 FBZ, 0.19–60 μg l −1 TBZ and 0.05–5 mg l −1 W were achieved. Relative standard deviations ( n =10) were 0.2% for 100 μg l −1 CBL and 2.4 μg l −1 FBZ, 0.7% for 8 μg l −1 TBZ and 1.0% for 1 mg l −1 W. The proposed automated methodology, which handles 17 samples/h, was validated and applied to spiked real water samples with very satisfactory results.
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Sequential injection analysis for the determination of Fuberidazole and thiabendazole by variable-angle scanning fluorescence spectrometry
Analytica Chimica Acta, 2001Co-Authors: G De Armas, Eduardo Becerra, Andreu Cladera, J.m. Estela, Víctor CerdàAbstract:Abstract A study of the behaviour of Fuberidazole (FBZ) (2-(2′-furyl)benzimidazole), and thiabendazole (TBZ) (2-(thiazol-4-yl)benzimidazole) in a sequential injection system with a fluorimetric detector has been performed. Several variables such as pH, composition of buffers, volumes of sample and reagents, addition order, geometry of mixing coil and spectrofluorimetric parameters have been optimised. A pH 2 buffer solution was found to be optimal for both FBZ and TBZ. The calibration graphs are linear between 0.04 and 10 μg l−1 for FBZ and between 0.08 and 20 μg l−1 for TBZ with 3σ detection limits of 0.012 and 0.02 μg l−1, respectively. The relative standard deviation (n=10) was 0.3% for 1 μg l−1 of FBZ and 0.5% for 2 μg l−1 of TBZ. Resolution of the system was carried out by applying a multiple linear regression (MLR) calibration model. The method was applied to the determination of both fungicides added to natural waters. Recoveries between 96 and 106% were achieved.
M. Martínez Galera - One of the best experts on this subject based on the ideXlab platform.
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Correction of predicted concentration in the use of solvent-based calibration lines for determining carbendazim, Fuberidazole and thiabendazole in water after a SPE step.
Talanta, 2003Co-Authors: D. Picón Zamora, M. Martínez Galera, A. Garrido Frenich, J. L. Martínez Vidal, J.l. López González, Manuel R. ArahalAbstract:This paper addresses an attempt to overcome the deviation that results from the use of a solid phase extraction (SPE) procedure for extracting trace levels of three benzimidazole pesticides (carbendazim, Fuberidazole and thiabendazole) from water samples, for their subsequent quantitative determination by spectrofluorimetry, using univariate calibration. The deviation is due to an attenuation effect originating in the C18 cartridge used in the SPE step. The approach developed is based on the calculation of a correction factor (fc) that is dependent on the signal measured after the SPE step. In order to calculate fc a study of the intermediate precision of two calibration graphs (with and without SPE) was performed. The fc was added to the predicted concentrations for the analytes using a calibration graph for pure solvent, built every time that the analysis is done. In addition, predictions were made using both average calibration graphs obtained from the intermediate precision study. In this study, the first of these three options was shown to improve the accuracy of predictions in the presence of matrix effects.
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Application of GRAM and TLD to the resolution and quantitation of real complex multicomponent mixtures by fluorescence spectroscopy
Analytical and Bioanalytical Chemistry, 2003Co-Authors: A. Garrido Frenich, D. Picón Zamora, M. Martínez Galera, J. L. Martínez VidalAbstract:The application of the generalised rank annihilation method (GRAM) and the trilinear decomposition (TLD) method to the resolution and quantitation of fluorescence excitation–emission matrices of a ternary mixture of pesticides, carbendazim, Fuberidazole, and thiabendazole, with overlapped spectra is described. The results obtained with both methods are compared and evaluated using measures of similarity (correlation coefficients) between the real and estimated spectra. Both approaches have been tested using augmented data matrices containing only two samples, but none of these methods succeeded completely in resolution of the system. When TLD was applied to augmented data matrices containing more than two samples better performance was achieved. To illustrate the application of both algorithms to real samples, they were used in the analysis of water samples containing the target pesticides. Again, TLD had an advantage over GRAM because the ability to analyse data from multiple (more than two) samples simultaneously allowed the resolution of the mixtures.
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Determination of carbendazim, Fuberidazole and thiabendazole by three-dimensional excitation–emission matrix fluorescence and parallel factor analysis
Analytica Chimica Acta, 2003Co-Authors: M.j Rodrı́guez-cuesta, D. Picón Zamora, M. Martínez Galera, Ricard Boque, F X Rius, A. Garrido FrenichAbstract:Abstract We simultaneously determined carbendazim, Fuberidazole and thiabendazole by excitation–emission matrix (EEM) fluorescence in combination with parallel factor analysis (PARAFAC). Three-way deconvolution provided the pure analyte spectra from which we estimated the selectivity and sensitivity of the pesticides, and the relative concentration in the mixtures from which we established a linear calibration. Special attention was given calculating such figures of merit as precision, sensitivity and limit of detection (LOD), derived from the univariate calibration curve. The method, which had a relative precision of around 2–3% for the three pesticides, provided limits of detection of 20 ng ml −1 for carbendazim, 4.7 ng ml −1 for thiabendazole and 0.15 ng ml −1 for Fuberidazole. The accuracy of the method, evaluated through the root mean square error of prediction (RMSEP), was 27.5, 1.4, and 0.03 ng ml −1 , respectively, for each of the pesticides.
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Standardization of SPE signals in multicomponent analysis of three benzimidazolic pesticides by spectrofluorimetry
Analytica Chimica Acta, 2003Co-Authors: A. Garrido Frenich, D. Picón Zamora, J. L. Martínez Vidal, M. Martínez GaleraAbstract:Piecewise direct standardization (PDS) is applied to multivariate standardization of fluorescence signals using partial least squares (PLS) and principal component regression (PCR) as the calibration models. The multivariate standardization was used to transfer spectra obtained after a step of solid phase extraction (SPE) to spectra registered in pure solvent in the determination of carbendazim, Fuberidazole and thiabendazole in water samples. The influential parameters, such as tolerance, window size and the number of samples of the standardization subset were optimized by means of the root mean squared error of prediction (RMSEP). Similar RMSEP values were obtained by PLS and PCR using the optimized influential parameters in the standardization. However, better predictions of the compounds were obtained in test set by the PLS model.
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Resolution (and quantitation) of mixtures with overlapped spectra by orthogonal projection approach and alternating least squares
Analytica Chimica Acta, 2001Co-Authors: A. Garrido Frenich, D. Picón Zamora, J. L. Martínez Vidal, M. Martínez GaleraAbstract:Abstract Resolution and quantitative determination of a mixture of overlapped pesticides, carbendazim, Fuberidazole and thiabendazole, in fluorescence spectroscopy by multivariate curve resolution–orthogonal projection approach (MCR–OPA) and by multivariate curve resolution–alternating least squares (MCR–ALS) is shown. Both approaches have been tested using a single matrix (two-way data) or an augmented matrix containing several data matrices simultaneously (three-way data). Augmented matrix data analysis showed an improvement in the recovery of the spectral profiles in both MCR methods. On the other hand, the influence of the pesticide concentrations in the MCR–ALS resolution power was evaluated using measures of dissimilarity between the real and the estimated excitation spectra, and correlations >0.96 were obtained at concentration levels higher than the quantitation limit.
Soledad Rubio - One of the best experts on this subject based on the ideXlab platform.
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Determination of benzimidazolic fungicides in fruits and vegetables by supramolecular solvent-based microextraction/liquid chromatography/fluorescence detection.
Analytica chimica acta, 2009Co-Authors: Antonia Moral, María Dolores Sicilia, Soledad RubioAbstract:Abstract A supramolecular solvent consisting of vesicles, made up of equimolecular amounts of decanoic acid (DeA) and tetrabutylammonium decanoate (Bu4NDe), dispersed in a continuous aqueous phase, is proposed for the extraction of benzimidazolic fungicides (BFs) from fruits and vegetables. Carbendazim (CB), thiabendazole (TB) and Fuberidazole (FB) were extracted in a single step and no clean-up or concentration of extracts was needed. The high extraction efficiency obtained for BFs was a result of the different types of interactions provided by the supramolecular solvent (e.g. hydrophobic and hydrogen bonds) and the high number of solubilisation sites it contains. Besides simple and efficient, the proposed extraction approach was rapid, low-cost, environment friendly and it was implemented using conventional lab equipments. The target analytes were determined in the supramolecular extract by LC/fluorescence detection. They were separated in a Kromasil C18 (5 μm, 150 mm × 4.6 mm) column using isocratic elution [mobile phase: 60:40 (v/v) 50 mM phosphate buffer (pH 4)/methanol] and quantified at 286/320 nm (CB) and 300/350 nm (TB and FB) excitation/emission wavelengths, respectively. Quantitation limits provided by the supramolecular solvent-based microextraction (SUSME)/LC/fluorescence detection proposed method for the determination of CB, TB and FB in fruits and vegetables were 14.0, 1.3 and 0.03 μg kg−1, respectively, values far below the current maximum residue levels (MRLs) established by the European Union, i.e. 100–2000 μg kg−1 for CB, 50–5000 μg kg−1 for TB and 50 μg kg−1 for FB. The precision of the method, expressed as relative standard deviation, for inter-day measurements (n = 13) was 3.3% for CB (50 μg kg−1), 3.5% for TB (10 μg kg−1) and 2.8% for FB (0.5 μg kg−1) and recoveries for fruits (oranges, tangerines, lemons, limes, grapefruits, apples, pears and bananas) and vegetables (potatoes and lettuces) fortified at the μg kg−1 level were in the interval 93–102%.
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Supramolecular solvent-based extraction of benzimidazolic fungicides from natural waters prior to their liquid chromatographic/fluorimetric determination
Journal of chromatography. A, 2009Co-Authors: Antonia Moral, María Dolores Sicilia, Soledad RubioAbstract:Abstract A supramolecular solvent made up of vesicles of decanoic acid in the nano- and microscale regimes dispersed in a continuous aqueous phase is proposed for the extraction/preconcentration of benzimidazolic fungicides (BFs) from river and underground water samples prior to their determination by liquid chromatography (LC)/fluorimetry. The solvent is produced from the coacervation of decanoic acid aqueous vesicles by the action of tetrabutylammonium (Bu4N+). Carbendazim (CB), thiabendazole (TB) and Fuberidazole (FB) are extracted on the basis of hydrophobic and π-cation interactions and the formation of hydrogen bonds. The extraction provides high preconcentration factors (160 for CB and 190 for TB and FB), requires a short time (the procedure takes less than 20 min and several samples can be simultaneously processed) and a low sample volume (20 mL), and avoids the use of toxic organic solvents. Because of the absence of matrix interferences and the low viscosity of the extracts, these can be directly injected into the chromatographic system without the need of cleaning-up or diluting them. Recoveries are not influenced by the presence of salt concentrations up to 1 M. The proposed method provides detection limits for the determination of CB, TB and FB in natural waters of 32, 4 and 0.1 ng L−1, respectively, and a precision, expressed as relative standard deviation (n = 11) of 5.5% for CB (100 ng L−1), 4.0% for TB (80 ng L−1) and 2.5% for FB (30 ng L−1). Recoveries obtained by applying this approach to the analysis of river and underground water samples fortified at the ng L−1 level are in the intervals 75–83, 95–102 and 97–101% for CB, TB and FB, respectively.
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Sodium dodecyl sulphate-coated alumina for the extraction/preconcentration of benzimidazolic fungicides from natural waters prior to their quantification by liquid chromatography/fluorimetry
Analytica Chimica Acta, 2006Co-Authors: Antonia Moral, María Dolores Sicilia, Soledad Rubio, Dolores Pérez-benditoAbstract:Abstract Sodium dodecyl sulphate (SDS)-coated alumina was used for the extraction/preconcentration of benzimidazolic pesticides (BFs) [carbendazim (CB), thiabendazole (TB) and Fuberidazole (FB)] from river and underground water. SDS admicelles were required to get quantitative retention of BFs. Adsolubilization of analytes occurred through hydrophobic and electrostatic interactions. Methanol (1 ml) provided quantitative elution of the target analytes for all the samples analyzed. The high breakthrough volumes obtained (400 ml for CB and 1 l for BF and FB) and the low eluent volume used resulted in very high preconcentration factors (between 400 and 1000). Calcium was found to decrease BFs retention due to the disruption of SDS admicelles; however, this interference was easily removed by precipitation with SDS prior to BFs adsolubilization. The accuracy of the proposed method was assessed by studying recoveries of BFs in natural waters at two spiking concentration levels (80, 40 and 4 ng l −1 , and 400, 200 and 20 ng l −1 for CB, TB and FB, respectively); mean recoveries in the intervals 96–105% and 98–108% were obtained for river and underground water samples, respectively.
A. Garrido Frenich - One of the best experts on this subject based on the ideXlab platform.
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Correction of predicted concentration in the use of solvent-based calibration lines for determining carbendazim, Fuberidazole and thiabendazole in water after a SPE step.
Talanta, 2003Co-Authors: D. Picón Zamora, M. Martínez Galera, A. Garrido Frenich, J. L. Martínez Vidal, J.l. López González, Manuel R. ArahalAbstract:This paper addresses an attempt to overcome the deviation that results from the use of a solid phase extraction (SPE) procedure for extracting trace levels of three benzimidazole pesticides (carbendazim, Fuberidazole and thiabendazole) from water samples, for their subsequent quantitative determination by spectrofluorimetry, using univariate calibration. The deviation is due to an attenuation effect originating in the C18 cartridge used in the SPE step. The approach developed is based on the calculation of a correction factor (fc) that is dependent on the signal measured after the SPE step. In order to calculate fc a study of the intermediate precision of two calibration graphs (with and without SPE) was performed. The fc was added to the predicted concentrations for the analytes using a calibration graph for pure solvent, built every time that the analysis is done. In addition, predictions were made using both average calibration graphs obtained from the intermediate precision study. In this study, the first of these three options was shown to improve the accuracy of predictions in the presence of matrix effects.
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Application of GRAM and TLD to the resolution and quantitation of real complex multicomponent mixtures by fluorescence spectroscopy
Analytical and Bioanalytical Chemistry, 2003Co-Authors: A. Garrido Frenich, D. Picón Zamora, M. Martínez Galera, J. L. Martínez VidalAbstract:The application of the generalised rank annihilation method (GRAM) and the trilinear decomposition (TLD) method to the resolution and quantitation of fluorescence excitation–emission matrices of a ternary mixture of pesticides, carbendazim, Fuberidazole, and thiabendazole, with overlapped spectra is described. The results obtained with both methods are compared and evaluated using measures of similarity (correlation coefficients) between the real and estimated spectra. Both approaches have been tested using augmented data matrices containing only two samples, but none of these methods succeeded completely in resolution of the system. When TLD was applied to augmented data matrices containing more than two samples better performance was achieved. To illustrate the application of both algorithms to real samples, they were used in the analysis of water samples containing the target pesticides. Again, TLD had an advantage over GRAM because the ability to analyse data from multiple (more than two) samples simultaneously allowed the resolution of the mixtures.
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Determination of carbendazim, Fuberidazole and thiabendazole by three-dimensional excitation–emission matrix fluorescence and parallel factor analysis
Analytica Chimica Acta, 2003Co-Authors: M.j Rodrı́guez-cuesta, D. Picón Zamora, M. Martínez Galera, Ricard Boque, F X Rius, A. Garrido FrenichAbstract:Abstract We simultaneously determined carbendazim, Fuberidazole and thiabendazole by excitation–emission matrix (EEM) fluorescence in combination with parallel factor analysis (PARAFAC). Three-way deconvolution provided the pure analyte spectra from which we estimated the selectivity and sensitivity of the pesticides, and the relative concentration in the mixtures from which we established a linear calibration. Special attention was given calculating such figures of merit as precision, sensitivity and limit of detection (LOD), derived from the univariate calibration curve. The method, which had a relative precision of around 2–3% for the three pesticides, provided limits of detection of 20 ng ml −1 for carbendazim, 4.7 ng ml −1 for thiabendazole and 0.15 ng ml −1 for Fuberidazole. The accuracy of the method, evaluated through the root mean square error of prediction (RMSEP), was 27.5, 1.4, and 0.03 ng ml −1 , respectively, for each of the pesticides.
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Standardization of SPE signals in multicomponent analysis of three benzimidazolic pesticides by spectrofluorimetry
Analytica Chimica Acta, 2003Co-Authors: A. Garrido Frenich, D. Picón Zamora, J. L. Martínez Vidal, M. Martínez GaleraAbstract:Piecewise direct standardization (PDS) is applied to multivariate standardization of fluorescence signals using partial least squares (PLS) and principal component regression (PCR) as the calibration models. The multivariate standardization was used to transfer spectra obtained after a step of solid phase extraction (SPE) to spectra registered in pure solvent in the determination of carbendazim, Fuberidazole and thiabendazole in water samples. The influential parameters, such as tolerance, window size and the number of samples of the standardization subset were optimized by means of the root mean squared error of prediction (RMSEP). Similar RMSEP values were obtained by PLS and PCR using the optimized influential parameters in the standardization. However, better predictions of the compounds were obtained in test set by the PLS model.
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Resolution (and quantitation) of mixtures with overlapped spectra by orthogonal projection approach and alternating least squares
Analytica Chimica Acta, 2001Co-Authors: A. Garrido Frenich, D. Picón Zamora, J. L. Martínez Vidal, M. Martínez GaleraAbstract:Abstract Resolution and quantitative determination of a mixture of overlapped pesticides, carbendazim, Fuberidazole and thiabendazole, in fluorescence spectroscopy by multivariate curve resolution–orthogonal projection approach (MCR–OPA) and by multivariate curve resolution–alternating least squares (MCR–ALS) is shown. Both approaches have been tested using a single matrix (two-way data) or an augmented matrix containing several data matrices simultaneously (three-way data). Augmented matrix data analysis showed an improvement in the recovery of the spectral profiles in both MCR methods. On the other hand, the influence of the pesticide concentrations in the MCR–ALS resolution power was evaluated using measures of dissimilarity between the real and the estimated excitation spectra, and correlations >0.96 were obtained at concentration levels higher than the quantitation limit.
D. Picón Zamora - One of the best experts on this subject based on the ideXlab platform.
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Correction of predicted concentration in the use of solvent-based calibration lines for determining carbendazim, Fuberidazole and thiabendazole in water after a SPE step.
Talanta, 2003Co-Authors: D. Picón Zamora, M. Martínez Galera, A. Garrido Frenich, J. L. Martínez Vidal, J.l. López González, Manuel R. ArahalAbstract:This paper addresses an attempt to overcome the deviation that results from the use of a solid phase extraction (SPE) procedure for extracting trace levels of three benzimidazole pesticides (carbendazim, Fuberidazole and thiabendazole) from water samples, for their subsequent quantitative determination by spectrofluorimetry, using univariate calibration. The deviation is due to an attenuation effect originating in the C18 cartridge used in the SPE step. The approach developed is based on the calculation of a correction factor (fc) that is dependent on the signal measured after the SPE step. In order to calculate fc a study of the intermediate precision of two calibration graphs (with and without SPE) was performed. The fc was added to the predicted concentrations for the analytes using a calibration graph for pure solvent, built every time that the analysis is done. In addition, predictions were made using both average calibration graphs obtained from the intermediate precision study. In this study, the first of these three options was shown to improve the accuracy of predictions in the presence of matrix effects.
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Application of GRAM and TLD to the resolution and quantitation of real complex multicomponent mixtures by fluorescence spectroscopy
Analytical and Bioanalytical Chemistry, 2003Co-Authors: A. Garrido Frenich, D. Picón Zamora, M. Martínez Galera, J. L. Martínez VidalAbstract:The application of the generalised rank annihilation method (GRAM) and the trilinear decomposition (TLD) method to the resolution and quantitation of fluorescence excitation–emission matrices of a ternary mixture of pesticides, carbendazim, Fuberidazole, and thiabendazole, with overlapped spectra is described. The results obtained with both methods are compared and evaluated using measures of similarity (correlation coefficients) between the real and estimated spectra. Both approaches have been tested using augmented data matrices containing only two samples, but none of these methods succeeded completely in resolution of the system. When TLD was applied to augmented data matrices containing more than two samples better performance was achieved. To illustrate the application of both algorithms to real samples, they were used in the analysis of water samples containing the target pesticides. Again, TLD had an advantage over GRAM because the ability to analyse data from multiple (more than two) samples simultaneously allowed the resolution of the mixtures.
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Determination of carbendazim, Fuberidazole and thiabendazole by three-dimensional excitation–emission matrix fluorescence and parallel factor analysis
Analytica Chimica Acta, 2003Co-Authors: M.j Rodrı́guez-cuesta, D. Picón Zamora, M. Martínez Galera, Ricard Boque, F X Rius, A. Garrido FrenichAbstract:Abstract We simultaneously determined carbendazim, Fuberidazole and thiabendazole by excitation–emission matrix (EEM) fluorescence in combination with parallel factor analysis (PARAFAC). Three-way deconvolution provided the pure analyte spectra from which we estimated the selectivity and sensitivity of the pesticides, and the relative concentration in the mixtures from which we established a linear calibration. Special attention was given calculating such figures of merit as precision, sensitivity and limit of detection (LOD), derived from the univariate calibration curve. The method, which had a relative precision of around 2–3% for the three pesticides, provided limits of detection of 20 ng ml −1 for carbendazim, 4.7 ng ml −1 for thiabendazole and 0.15 ng ml −1 for Fuberidazole. The accuracy of the method, evaluated through the root mean square error of prediction (RMSEP), was 27.5, 1.4, and 0.03 ng ml −1 , respectively, for each of the pesticides.
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Standardization of SPE signals in multicomponent analysis of three benzimidazolic pesticides by spectrofluorimetry
Analytica Chimica Acta, 2003Co-Authors: A. Garrido Frenich, D. Picón Zamora, J. L. Martínez Vidal, M. Martínez GaleraAbstract:Piecewise direct standardization (PDS) is applied to multivariate standardization of fluorescence signals using partial least squares (PLS) and principal component regression (PCR) as the calibration models. The multivariate standardization was used to transfer spectra obtained after a step of solid phase extraction (SPE) to spectra registered in pure solvent in the determination of carbendazim, Fuberidazole and thiabendazole in water samples. The influential parameters, such as tolerance, window size and the number of samples of the standardization subset were optimized by means of the root mean squared error of prediction (RMSEP). Similar RMSEP values were obtained by PLS and PCR using the optimized influential parameters in the standardization. However, better predictions of the compounds were obtained in test set by the PLS model.
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Resolution (and quantitation) of mixtures with overlapped spectra by orthogonal projection approach and alternating least squares
Analytica Chimica Acta, 2001Co-Authors: A. Garrido Frenich, D. Picón Zamora, J. L. Martínez Vidal, M. Martínez GaleraAbstract:Abstract Resolution and quantitative determination of a mixture of overlapped pesticides, carbendazim, Fuberidazole and thiabendazole, in fluorescence spectroscopy by multivariate curve resolution–orthogonal projection approach (MCR–OPA) and by multivariate curve resolution–alternating least squares (MCR–ALS) is shown. Both approaches have been tested using a single matrix (two-way data) or an augmented matrix containing several data matrices simultaneously (three-way data). Augmented matrix data analysis showed an improvement in the recovery of the spectral profiles in both MCR methods. On the other hand, the influence of the pesticide concentrations in the MCR–ALS resolution power was evaluated using measures of dissimilarity between the real and the estimated excitation spectra, and correlations >0.96 were obtained at concentration levels higher than the quantitation limit.
