José Luis Pérez Pavón

Detection of adulterants in olive oil by headspace-mass spectrometry.

In the present work, we propose the use of direct coupling of a headspace sampler to a mass spectrometer for the detection of adulterants in olive oil. Samples of olive oils were mixed with different proportions of sunflower oil and olive-pomace oil, respectively, and patterns of the volatile compounds in the original and mixed samples were generated. Application of the linear discriminant analysis technique to the data from the signals was sufficient to differentiate the adulterated from the non-adulterated oils and to discriminate the type of adulteration. The results obtained revealed 100% success in classification and close to 100% in prediction. The main advantages of the proposed methodology are the speed of analysis (since no prior sample preparation steps are required), low cost, and the simplicity of the measuring process.

Cloud point preconcentration and flame atomic absorption spectrometry : application to the determination of cadmium

Cloud point methodology has been successfully used for the preconcentration of trace amounts of cadmium as a prior step to its determination by flame atomic absorption spectrometry. A procedure based on the formation of a complex with 1-(2-pyridylazo)-2-naphthol (PAN) is used for the preconcentration of cadmium in a surfactant-rich phase of Triton X-114. The chemical variables affecting the preconcentration step and the viscosity of the solution affecting the detection process have been optimized. Under the optimum conditions, a precision of 3.0% was achieved. The preconcentration of only 15 ml of sample with 0.05% Triton X-114 permits the detection of <0.4 ppb of cadmium with a concentration factor of 120.

Electronic nose based on metal oxide semiconductor sensors as a fast alternative for the detection of adulteration of virgin olive oils

Abstract An “electronic nose” has been used for the detection of adulterations of virgin olive oil. The system, comprising 12 metal oxide semiconductor sensors, was used to generate a pattern of the volatile compounds present in the samples. Prior to different supervised pattern recognition treatments, feature selection techniques were employed to choose a set of optimally discriminant variables. Linear discriminant analysis (LDA), quadratic discriminant analysis (QDA) and artificial neural networks (ANN) were applied. Excellent results were obtained in the differentiation of adulterated and non-adulterated olive oils and it was even possible to identify the type of oil used in the adulteration. Promising results were also obtained as regards quantification of the percentages of adulteration.

Micelle-mediated methodology for the preconcentration of uranium prior to its determination by flow injection

Cloud point extraction has been used for the preconcentration of uranium, prior to its determination by flow injection. The non-ionic surfactant employed was Triton X-114 and the reagent chosen to form a hydrophobic chelate of uranium was 1-(2-pyridylazo)-2-naphthol. The optimum conditions for the preconcentration and determination of uranium have been studied. This methodology has been applied to the determination of trace amounts of uranium in tap and river waters from Salamanca.

Cloud Point Methodology : A New Approach for Preconcentration and Separation in Hydrodynamic Systems of Analysis

The analytical potential shown by the cloud point phenomenon for the separation and preconcentration of different analytes as an alternative method to other separation techniques is studied. We offer and discuss several examples that can be applied in flow injection analysis and high performance liquid chromatography with both optical (UV and fluorescence) and electrochemical detection.

Classification of vegetable oils by linear discriminant analysis of Electronic Nose data

The purpose of this work was to attempt to classify edible vegetable oils by chemometric treatment of the data obtained from an array of gas sensors. A commercial Electronic Nose (FOX 2000) comprising six metal oxide semiconductor sensors was used to generate a pattern of the volatile compounds present in the samples. Linear discriminant analysis (LDA) was applied to the patterns generated to achieve several classification tasks. The procedure for obtaining the signals and the chemometric treatment are rapid and simple, and provide classification and prediction capabilities higher than 95%.

Electronic nose based on metal oxide semiconductor sensors and pattern recognition techniques: characterisation of vegetable oils

Different supervised pattern recognition treatments were applied to the signals generated by an electronic nose for the classification of vegetable oils. The system, comprising six metal oxide semiconductor sensors, was used to generate a pattern of the volatile compounds present in the samples. Feature selection techniques were employed to choose a set of optimally discriminant variables. The K-nearest neighbours (KNN), linear discriminant analysis (LDA), quadratic discriminant analysis (QDA), soft independent modelling of class analogy (SIMCA) and artificial neural networks (ANN) were applied to model the different classes. The results obtained indicated good classification and prediction capabilities, the neural networks being those that afforded the best results.

Analytical applications of membrane extraction in chromatography and electrophoresis.

An overview of the analytical applications of membrane-based systems for sample enrichment in chromatography and capillary electrophoresis is presented. A brief introduction to the different types of membranes and the main forces related to the transport through them is also given.

Microextraction by packed sorbent for the analysis of pharmaceutical residues in environmental water samples by in situ derivatization-programmed temperature vaporizer–gas chromatography–mass spectrometry

The present work describes the development and validation of a method for the determination of five non-steroidal anti-inflammatory drugs (NSAIDs: clofibric acid, ibuprofen, naproxen, diclofenac and ketoprofen) in water samples. The fully automated method includes in situ aqueous derivatization followed by analyte enrichment by microextraction by packed sorbent (MEPS) coupled directly to programmed temperature vaporizer-gas chromatography-mass spectrometry (PTV-GC-MS). The MEPS variables, such as sample volume, elution solvent, elution volume, fill and injection speed and washing steps were optimized. It was possible to use the MEPS polymer (silica-C18) 250 times. Ibuprofen-d3 was used as internal standard. The reproducibility of the method, calculated as the relative standard deviation (RSD), was below 10% for all compounds. Detection limits in ultrapure water were between 3.0 and 110 ngL(-1) for ibuprofen and ketoprofen, respectively. External calibration was used in the determination of NSAIDs in several types of water samples, including tap, river, sea and influent and effluent wastewater. The results obtained revealed the presence of ibuprofen and naproxen in the influent wastewater sample and of naproxen in the effluent wastewater sample.

In situ aqueous derivatization as sample preparation technique for gas chromatographic determinations

The use of derivatization reactions is a common practice in analytical laboratories. Although in many cases it is tedious and time-consuming, it does offer a good alternative for the determination of analytes not compatible to gas chromatography. Many of the reactions reported in the literature occur in organic medium. However, in situ aqueous derivatization reactions, which can be performed directly in aqueous medium, offer important advantages over those mentioned above, such as no need of a previous extraction step and easy automation. Here we review the most recent developments and applications of in situ aqueous derivatization. The discussion focuses on the derivatization reactions used for the determination of alcohols and phenols, carboxylic acids, aldehydes and ketones, nitrogen-containing compounds and thiols in different aqueous matrices, such as environmental, biological and food samples. Several reactions are described for each functional group (acylation, alkylation, esterification, among others) and, in some cases, the same reagents can be used for several functional groups, such that there is an unavoidable overlap between sections. Finally, attention is also focused on the techniques used for the introduction of the derivatives formed in the aqueous medium into the chromatographic system. The implementation of in situ aqueous derivatization coupled to preconcentration techniques has permitted the enhancement of recoveries and improvements in the separation, selectivity and sensitivity of the analytical methods.