J.L. Vílchez

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.

Determination of imidacloprid in water and soil samples by gas chromatography-mass spectrometry

A method for determination of imidacloprid in water and soil samples, previous hydrolysis in basic medium, followed by gas chromatography-mass spectrometry and selected ion monitoring. A 250-ml sample water was previously heated in basic medium to give a hydrolysis compound of adequate volatility. The hydrolysis product which was extracted and isolated with chloroform was identified and found to be suitable for gas chromatography analysis. Further, a clean-up is not necessary using the selected ion monitoring mode. [2H10]Anthracene was used as an internal standard. The applicable concentration range was 5–20 μg l−1. Detection limit was 0.16 μg l−1 for water and 1 μg kg−1 for soil samples. Their relative standard deviations established for different concentration levels were between 0.3 and 1%. It was applied to the check whether there was imidacloprid above these limits on waters and soil from Granada (Spain). The method was validated applying the standard addition methodology. Recovery levels of the method reached 100% in all cases.

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.

Determination of the antibacterial norfloxacin in human urine and serum samples by solid-phase spectrofluorimetry

A method for the determination of trace amounts of ofloxacin has been developed, based on solid-phase spectrofluorimetry. The relative fluorescence intensity of ofloxacin fixed on Sephadex SP C-25 gel was measured directly after packing the gel beads in a 1-mm silica cell, using a solid-phase attachment. The wavelengths of excitation and emission were 294 and 494 nm, respectively. The linear concentration range of application was 0.5-16.0 ng ml(-1) of ofloxacin, with a relative standard deviation of 1.1% (for a level of 8.0 ng ml(-1)) and a detection limit of 0.14 ng ml(-1). The method was applied to the determination of ofloxacin in human urine and serum samples. It was validated applying the standard addition methodology and using HPLC as a reference method. Recovery levels of the method reached 100% in all cases.

Trace determination of phenol, bisphenol A and bisphenol A diglycidyl ether in mixtures by excitation fluorescence following micro liquid–liquid extraction using partial least squares regression

The determination of phenol, bisphenol A and bisphenol A diglycidyl ether in mixtures was carried out by recording excitation fluorescence spectra between 245 and 290 nm with an emission wavelength of 306 nm. The proposed method involves a micro liquid–liquid extraction of sodium chloride saturated water samples with diethyl ether followed by direct fluorimetric analysis of the extracts in a 10 mm quartz cell with a 2 mm inside width and a volume of 400 µl. The excitation–emission spectra of these compounds overlap considerably, which does not permit their direct determination without previous separation by conventional methodologies. A method is proposed for the determination of these compounds by the use of a full-spectrum multivariate calibration method, partial least squares (PLS). A comparison between two PLS algorithms with different pre-processing methodologies was made. The experimental calibration matrix was designed with 19 samples. The concentrations were varied between 3.0 and 18.0 µg l–1 for phenol, 3.0 and 13.0 µg l–1 for bisphenol A and 5.0 and 30.0 µg l–1 for bisphenol A diglycidyl ether. The cross-validation method was used to select the number of factors. The proposed method, which applied the PLS-1 model with mean centred data, was used for the determination of these compounds in previously spiked water. The predicted concentrations were satisfactory in all cases.

On the estimate of blanks in differential pulse voltammetric techniques : application to detection limits evaluation as recommended by IUPAC

A new method to obtain the signal associated with a blank in differential pulse voltammetry and stripping voltammetry techniques is applied. The signal assigned to the blank is obtained by direct integration of the background noise extrapolated values of the base-peak width at different concentrations in order to obtain the zero concentration. Detection limits more amenable to a statistical evaluation are thus implemented, as recommended by the International Union of Pure and Applied Chemistry (IUPAC).

Determination of Trace Amounts of Carbaryl in Water by Solid Phase Spectrofluorimetry

Abstract A simple and sensitive spectrofluorimetric method for the determination of carbaryl residues in water is presented. Carbaryl is hydrolized in alkaline medium to 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. Spectral characteristics of 1-naphthol-gel system are described in detail. The applicable concentration range was 0.5–60.0 ng.ml−1, with a relative standard deviation of 0.9% and a detection limit of 0.1 ng.ml−1. The method was applied to the determination of carbaryl in natural waters.

Close overlapping discrimination of polycyclic aromatic hydrocarbons by synchronous scanning at variable-angle solid-phase spectrofluorimetry

Abstract The polycyclic aromatic hydrocarbons (PAHs) fluorene, acenaphthene and phenanthrene have been determined in water at trace levels by solid-phase variable-angle synchronous scanning spectrofluorimetry. These PAHs were previously fixed on Sephadex G-15 gel, and then packed in a quartz cell with a 1-mm pathlength. The fluorescence of the PAHs-gel system was measured directly using a solid-surface attachment. The applicable concentration ranges were 0.70–7.00 ng ml −1 for fluorene, 4.0–60.0 ng ml −1 for acenaphthene and 0.50–5.00 ng ml −1 for phenanthrene. The detection limits were 0.07 ng ml −1 , for fluorene, 0.4 ng ml −1 for acenaphthene and 0.05 ng ml −1 for phenanthrene, the relative standard deviations being 0.94%, 0.95% and 0.74%, respectively. The method was applied to the determination of the cited PAHs in waters of diverse provenance. The recoveries obtained were 93.0–105.0%.

Optimization of the composition and pH of the mobile phase used for separation and determination of a series of quinolone antibacterials regulated by the European Union

SummaryTo ensure the safety of human food the European Union (EU) has set tolerance levels for quinolone compounds in animal products, so screening and confirmatory analytical methods are required for monitoring of these drugs. In this work, the proportion of organic modifier and the pH of acetonitrile-water mixtures used as mobile phases were optimized for separation of a group of quinolones. Linear solvation energy relationship (LSER) formalism based on the single solvent polarity parameterETN was used to predict the chromatographic behaviour of the compounds as a function of the amount of acetonitrile in the mobile phase. Correlation between retention and the pH of aqueous-organic mobile phases has also been used to optimize mobile-phase pH. The optimized mobile phase was a linear gradient starting from 18∶82 (v/v) acetonitrileacetate + formate buffer, pH 2.5. Quality data were determined and were satisfactory. The method detection limit was approximately 10 ng mL−1 for most of the quinolones studied. The proposed mobile phase is compatible with mass spectrometric detection of the substances.