M. del Olmo

Determination of bisphenol A (BPA) in water by gas chromatography-mass spectrometry

Abstract A simple method for determination of bisphenol A in waters was developed using Gas Chromatography-Mass Spectrometry with a Selected Ion Monitoring (GC/MS-SIM). A 1000 ml water sample was extracted with dichloromethane in acid medium. No clean-up was necessary. Anthracene-d10 was used as an internal standard. The applicable concentration range was 2.5 to 10 ng ml−1 in water samples. The detection limit was 0.6 ng ml−1. The method was applied satisfactorily to the determination of oestrogenic environmental pollutants in sea water from Malaga (Spain) and spring water from the fertile plain of Granada (Spain). The method was validated using the standard addition methodology. The accuracy of the proposed method was verified by applying a Student t test. The relative standard deviations established for the linear concentration range was between 8.6 and 1.5%.

Kohonen artificial neural networks as a tool for wavelength selection in multicomponent spectrofluorimetric PLS modelling: application to phenol, o-cresol, m-cresol and p-cresol mixtures

Abstract Different strategies for wavelength selection for partial least squared (PLS) calibration models have been proposed. In this article, Kohonen artificial neural networks (K-ANN) are used to select optimal sets of wavelengths for PLS calibration of mixtures with stray overlapping. This kind of variable selection appears simple and very effective due to the well known high correlation of spectroscopic data; a measure of the multivariate correlation of the different wavelength subsets is also given. This strategy has been applied to the resolution of mixtures of phenol, o -cresol, m -cresol and p -cresol by spectrofluorimetry. The number of samples to obtain the calibration matrix is also reduced with respect to the number necessary when the full spectrum is used, and the predictive ability of the PLS method is improved.

Resolution of phenol, o-cresol, m-cresol and p-cresol mixtures by excitation fluorescence using partial least-squares (PLS) multivariate calibration

Abstract Determination of phenol, o-cresol, m-cresol and p-cresol has been carried out in mixtures of up to four components by recording excitation fluorescence spectra between 210 and 285 nm with an emission wavelength of 298 nm. The excitationemission spectra of these compounds are strongly overlapped, which does not permit their direct determination without previous separation by conventional methodologies. Here, a method is proposed for the determination of these chemicals by the use of a full-spectrum multivariate calibration method, partial least squares (PLS). The experimental calibration matrix was designed with 18 samples. The concentrations were varied between 100 and 900 μgl−1 for phenol, 150 and 900 μg l−1 for o-cresol and from 80 to 800 μg l−1 for m- and p-cresol. The cross-validation method was used to select the number of factors. To check the accuracy of the proposed method, the optimized model, obtained using PLS-1, was applied to the determination of these compounds in natural water and soil samples previously spiked with different amounts of each chemical.

Resolution of mixtures of three nonsteroidal anti-inflammatory drugs by fluorescence using partial least squares multivariate calibration with previous wavelength selection by Kohonen artificial neural networks.

A spectrofluorometric method for the quantitative determination of flufenamic, mefenamic and meclofenamic acids in mixtures has been developed by recording emission fluorescence spectra between 370 and 550 nm with an excitation wavelength of 352 nm. The excitation-emission spectra of these compounds are deeply overlapped which does not allow their direct determination without previous separation. The proposed method applies partial least squares (PLS) multivariate calibration to the resolution of this mixture using a set of wavelengths previously selected by Kohonen artificial neural networks (K-ANN). The linear calibration graphs used to construct the calibration matrix were selected in the ranges from 0.25 to 1.00 mug ml(-1) for flufenamic and meclofenamic acids, and from 1.00 to 4.00 mug ml(-1) for mefenamic acid. A cross-validation procedure was used to select the number of factors. The selected calibration model has been applied to the determination of these compounds in synthetic mixtures and pharmaceutical formulations.

Determination of bisphenol A (BPA) in the presence of phenol by first-derivative fluorescence following micro liquid-liquid extraction (MLLE).

Bisphenol A (BPA) in the presence of phenol is determined using a method based on first-derivative spectrofluorimetry. The proposed method involves a micro liquid-liquid extraction of sodium chloride saturated water samples with diethyl ether followed by direct fluorimetric analysis of extracts. The excitation spectra of both compounds in diethyl ether are recorded between 200 and 290 nm, with the emission wavelength at 306 nm. The first-derivative spectra were calculated, measuring the analytical signal for BPA at 239 nm. The concentration range over which the method was applied was 0.5-10.0 microg.l(-1) of BPA with relative standard deviations of 2.9% for a concentration of 4.0 microg.l(-1) of BPA. The detection limit was 0.07 microg.l(-1). The proposed method was applied satisfactorily to the determination of BPA in synthetic mixtures and water samples from different sources previously spiked with different amounts of these chemicals. Recovery values ranging from 93% to 112% were obtained for water samples.

Determination of trace amounts of carbaryl in water by solid-phase laser-induced fluorescence.

A quick and very sensitive method is proposed for the determination of the insecticide carbaryl, following transformation in 1-naphthol, using solid-phase fluorescence excited by a pulsed nitrogen laser and detected with a charge-coupled device. Carbaryl is hydrolized in an alkaline medium resulting in 1-naphthol. This hydrolysis product is fixed on QAE Sephadex A-25 gel at pH 11.20. The fluorescence of the gel, packed in a 1 mm silica cell, was measured directly using a solid-surface attachment. The detection limit obtained was 1.8 ng. A recovery study was carried out on several types of water samples to check the efficiency of the method. The results obtained are compared with data published in a previous paper where the LS-50 spectrofluorimeter was used. The detection and quantification limits are improved here by an order of magnitude.

Determination of bisphenol-a and related compounds in human saliva by gas chromatography—mass spectrometry

SummaryA simple and sensitive method for the determination of trace amounts of bisphenol-A (BPA), bisphenol-A diglycidyl dimethacrylate (bis-GMA), bisphenol-A dimethacrylate (bis-DMA) and triethyleneglycol dimethacrylate (TEGDMA) in human saliva is proposed. These materials are used in dental restorations, as composites and sealants, and are sometimes detected in human saliva after dental treatment. The proposed method involves protein precipitation using acetonitrile followed by acidification, evaporation of the solvent and dissolution with dichloromethane prior to injection into a GC-MS.Thermal derivatization in the injection system was used for the identification and quantification of bis-GMA. Clean-up is not necessary using SIM mode. Bisphenol-F (BPF) was used as internal standard. The linear range was 15 to 1000 μg·L−1 for BPA, 50 to 10 000 μg·L−1 for bis-GMA, 50 to 1000 μg·L−1 for bis-DMA and 1 to 100 μg·L−1 for TEGDMA.The detection limits were 3,15,10 and 0.3 μg·L−1 for BPA, bis-GMA, bis-DMA and TEGD-MA, respectively. Validation of the proposed method was carried out by using the standard addition methodology.Samples of 10 mL of human saliva collected 1 h after dental treatment were analysed in order to assess the applicability of the method to detect and quantify such compounds originated from methacrylic resins used in odontological treatment.

Determination of carbetamide in groundwater by micro liquid-liquid extraction and gas chromatography-mass spectrometry.

SummaryA method is proposed for the determination of carbetamide in water below European Union guidelines (detection limit,DL, below 0.1 μgL−1). Micro liquid-liquid extraction with dichloromethane affords carbetamide which is converted to aniline by hydrolysis. Identification and quantification of aniline was performed by GC-MS. The retention time was 4.24 min. Quantification was achieved by single-ion monitoring (SIM) atm/z 66 and 93. Clean-up is not necessary before SIM. Deuterated anthracene (2H10-anthracene) was used as internal standard. The method was used to determine carbetamide in different types of water sample spiked at very low concentration levels (0.13–10.00 μgL−1). TheDL was 0.04 μgL−1. The effect of the presence of other carbamates was also studied.