Antonio González-Casado

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%.

Determination of trace amounts of bisphenol F, bisphenol A and their diglycidyl ethers in wastewater by gas chromatography–mass spectrometry

A simple and sensitive method for the determination of trace amounts of bisphenol F, bisphenol A and their diglycidyl ethers in wastewater is proposed. The method involves a liquid‐liquid extraction (LLE) procedure using trichloromethane followed by a silylation step. Identification and quantification was performed by gas chromatography‐mass spectrometry (GC‐MS) using an HP1-MS column. The retention times were 6.59 and 7.02 min for BPF and BPA silylated, respectively, 8.30, 9.10 and 10.13 min for the three isomers of BFDGE and 11.12 min for BADGE. A clean-up is not necessary using SIM mode. Deuterated anthracene ( 2 H10-anthracene) was used as an internal standard. The detection limits obtained were 0.02, 0.006, 0.13 and 0.09m gl 1 for BPF, BPA, BFDGE and BADGE, respectively. The method was applied to the determination of these chemicals, as indicators of contamination by epoxy resins, in different types of spiked urban wastewater from Granada and Melilla (Spain) at concentration levels ranging from 0.06 to 2.50 m gl 1 for bisphenol F, 0.02 to 0.50m gl 1 for bisphenol A, 0.45 to 50.00m gl 1 for BFDGE and 0.30 to 50.00m gl 1 for BADGE.

Differential-pulse polarographic determination of the insecticide imidacloprid in commercial formulations

The reduction reaction of imidacloprid [1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine] at a mercury electrode shows two well-defined waves in the range of pH 2.0–11.0. The characteristics of the electrode processes were examined. The analyte captures four electrons in the first step and two in the second to give the hydroxylamine and amine derivatives, respectively. A differential-pulse polarographic method for the determination of imidacloprid based on the first reduction peak of this compound is presented. Britton-Robinson buffer was used as a supporting electrolyte and optimum pH value was found to be pH 8.O. The applicable concentration range was from 10 to 200 ng/ml, with a relative standard deviation of 1.5% (for a level of 80 ng/ml) and a detection limit of 3 ng/ml. The method has been satisfactorily applied to the determination of imidacloprid in commercial formulations.

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.

Determination of imidacloprid in vegetable samples by gas chromatography-mass spectrometry

A method for the determination of imidacloprid involving hydrolysis in basic medium followed by gas chromatography–mass spectrometry and selected ion monitoring was developed. The hydrolysis product which was extracted with chloroform was found to be suitable for gas chromatographic analysis. Further, clean-up is not necessary using the selected ion monitoring mode. [ 2 H 10 ]Anthracene was used as an internal standard. The applicable concentration range was 12.5–250.0 µg kg - 1 , the detection limit was 2.5 µg kg - 1 (98 pg) and the relative standard deviation at the 125.0 µg kg - 1 level was 0.7%. The method was applied to the determination of the imidaclorpid in vegetable samples (tomato, cucumber, pepper and green beans). Recovery levels were between 94.3% and 105.8%.

Quantification of blending of olive oils and edible vegetable oils by triacylglycerol fingerprint gas chromatography and chemometric tools

A reliable procedure for the identification and quantification of the adulteration of olive oils in terms of blending with other vegetable oils (sunflower, corn, seeds, sesame and soya) has been developed. From the analytical viewpoint, the whole procedure relies only on the results of the determination of the triacylglycerol profile of the oils by high temperature gas chromatography-mass spectrometry. The chromatographic profiles were pre-treated (baseline correction, peak alignment using iCoshift algorithm and mean centering) before building the models. At first, a class-modeling approach, Soft Independent Modeling of Class Analogy (SIMCA) was used to identify the vegetable oil used blending. Successively, a separate calibration model for each kind of blending was built using Partial Least Square (PLS). The correlation coefficients of actual versus predicted concentrations resulting from multivariate calibration models were between 0.95 and 0.99. In addition, Genetic algorithms (GA-PLS), were used, as variable selection method, to improve the models which yielded R(2) values higher than 0.90 for calibration set. This model had a better predictive ability than the PLS without feature selection. The results obtained showed the potential of this method and allowed quantification of blends of olive oil in the vegetable oils tested containing at least 10% of olive oil.

Multivariate analysis of HT/GC-(IT)MS chromatographic profiles of triacylglycerol for classification of olive oil varieties

The ability of multivariate analysis methods such as hierarchical cluster analysis, principal component analysis and partial least squares-discriminant analysis (PLS-DA) to achieve olive oil classification based on the olive fruit varieties from their triacylglycerols profile, have been investigated. The variations in the raw chromatographic data sets of 56 olive oil samples were studied by high-temperature gas chromatography with (ion trap) mass spectrometry detection. The olive oil samples were of four different categories (“extra-virgin olive oil”, “virgin olive oil”, “olive oil” and “olive-pomace” oil), and for the “extra-virgin” category, six different well-identified olive oil varieties (“hojiblanca”, “manzanilla”, “picual”, “cornicabra”, “arbequina” and “frantoio”) and some blends of unidentified varieties. Moreover, by pre-processing methods of chemometric (to linearise the response of the variables) such as peak-shifting, baseline (weighted least squares) and mean centering, it was possible to improve the model and grouping between different varieties of olive oils. By using the first three principal components, it was possible to account for 79.50% of the information on the original data. The fitted PLS-DA model succeeded in classifying the samples. Correct classification rates were assessed by cross-validation.

Chemiluminescence determination of carbofuran at trace levels in lettuce and waters by flow-injection analysis

A simple, fast chemiluminescence (CL) flow-injection (FI) method based on the reaction of luminol with KMnO(4) in alkaline medium has been described for the direct determination of carbofuran. The method is based on the enhancing effect in the emission light from the oxidation of luminol produced in presence of carbofuran. The optimisation of instrumental and chemical variables influencing the CL response of the method has been carried out by applying experimental design, using the proposed flow-injection manifold. Under the optimal conditions, the CL intensity was linear for a carbofuran concentration over the range of 0.06-0.5mugml(-1), with a detection limit of 0.02mugml(-1). The method has been successfully applied to the determination of carbofuran residues in spiked water and lettuce samples.

Application of selected ion monitoring to the analysis of triacylglycerols in olive oil by high temperature-gas chromatography/mass spectrometry.

The analysis of the triacylglycerol (TAG) composition of oils is a very challenging task, since the TAGs have very similar physico-chemical properties. In this work, a high temperature-gas chromatographic method coupled to electron ionization-mass spectrometry (HT-GC/EI-MS), in the Selected Ion Monitoring (SIM) mode, method was developed for the analysis of TAGs in the olive oil; this is a method suitable for routine analysis. This method was developed using commercially available standard TAGs. The TAGs studied were separated according to their equivalent carbon number and degree of unsaturation. The peak assignment was carried out by locating the characteristic fragment ions having the same retention time on the SIM profile such as [RCO+74](+) and [RCO+128](+) ions, due to the fatty acyl residues on sn-1, sn-2 and sn-3 positions of the TAG molecule and the [M-OCOR](+) ions corresponding to the acyl ions. The developed method was very useful to eliminate the interferences that appeared in the mass spectrum since electron ionization can prevent satisfactory interpretation of spectra.

The Use of β-Cyclodextrin Inclusion Complexes for the Analysis of Bisphenol a Residues in Water by Spectrofluorimetry

Abstract The application of β-cyclodextrin inclusion complexes to determine trace levels of bisphenol A (BPA) in aqueous solution by spectrofluorimetry was investigated. A 1:1 stoichiometry of the host-guest complex between β-CD and BPA, as well as the association constant was determined by using the changes in the fluorescence of BPA that occur when it is included in the hydrophobic cyclodextrin cavity. A simple and sensitive spectrofluorimetric method for the determination of BPA residues is presented; the applicable concentration range was 10.0 to 200.0 μgL−1. The detection limit obtained was 0.5 μg.L−1. The accuracy of the proposed method, was checked in the analysis of water samples from different sources previously spiked with different amounts of BPA.