M. de la Guardia

Efficiency of the microwave-assisted extraction of hydrocarbons and pesticides from sediments

Abstract A mixture of toluene and water is proposed for the microwave-assisted extraction of organic pollutants, hydrocarbons and pesticides, from marine sediments. The effect of experimental conditions, such as microwave power and irradiation time, on the extraction of linear, unresolved and polycyclic aromatic hydrocarbons as well as PCBs and DDTs has been evaluated using real marine sediment samples. Values found by Soxhlet and ultrasonic extraction were employed to evaluate the efficiency of the microwave-assisted extraction. Analytical determinations were carried out by gas chromatography using FID, ECD and MS detectors. For 2 g of a dry sediment, an extraction time of 6 min with 10 ml toluene and 1 ml water provides a complete extraction of 15 linear hydrocarbons, 19 polycyclic aromatic hydrocarbons, 4 DDTs and 6 PCBs congeners. Recovery percentage values varies from 107% to 98.5% as compared with the Soxhlet extraction.

PLS-NIR determination of total sugar, glucose, fructose and sucrose in aqueous solutions of fruit juices

Abstract An analytical procedure has been developed for the direct determination of sugars in fruit juice samples. The method is based on the partial least-squares (PLS) treatment of first derivative near infrared (NIR) spectroscopic data obtained between 1200 and 2450 nm, using 1 mm pathlength cell and a multicomponent calibration set, including seven binary mixtures and 10 ternary mixtures of glucose, fructose and sucrose. The limit of detection values found are of the order of 0.2 g/100 ml for total sugar and 0.2, 0.4 and 0.5 g/100 ml for glucose, fructose and sucrose, respectively. Relative standard deviation values obtained vary from 0.4% to 2.3% for six independent measurements of individual sugar concentrations from 15.4 to 2.4 g/100 ml and 0.03% for total sugar of the order of 20 g/100 ml. Average recovery percentages of 99 ± 2 for total sugar and between 98 ± 4 and 100 ± 4 for single sugar determinations evidence the applicability of the methodology developed for the analysis of juice samples.

A review of non-chromatographic methods for speciation analysis.

This manuscript overviews relevant scientific literature concerning speciation of trace elements by using non-chromatographic methods. The main principles of the different strategies proposed in the published works and their advantages and drawbacks are discussed in order to provide to the readers an appropriate picture of the state-of the-art of fast and cheap methodologies available to obtain information about the presence of different chemical forms of trace elements in environmental, clinical and food samples. A selection of the methods proposed for the speciation of the different elements studied was also provided together with their main features.

Chromium speciation using activated alumina microcolumns and sequential injection analysis-flame atomic absorption spectrometry

A new procedure has been developed for chromium speciation in water by sequential injection analysis and flame atomic absorption spectrometry. The method involves the online retention of Cr(VI) anionic species and Cr(III) cationic species on alumina microcolumns, prepared by packing activated alumina in polytetrafluoroethylene tubes, followed by selective elution of Cr(VI) with 2 mol l(-1) NH(4)OH and of Cr(III) with 0.2 mol l(-1) HNO(3). Studies were carried out on the effect of retention and elution conditions for both Cr species. The limit of detection values, established as the concentration corresponding to three times the standard deviation of blank measurements divided by the slope of the calibration line, achieved were 42 mug l(-1) for Cr(VI) and 81 mug l(-1) for Cr(III). The relative standard deviation of three independent determination of natural spiked samples were lower than 10% for concentration levels between 0.5 and 2 mg l(-1) of Cr. The developed procedure was applied to the analysis of two effluent sewage waters, and results obtained compared well with those obtained by a batch procedure. Recovery studies on natural spiked samples provided results between 93 and 103% for Cr(VI) and from 100 to 106% for Cr(III) for samples spiked with single species. For samples spiked with both Cr(VI) and Cr(III), the average recoveries varied from 86 to 101% for Cr(VI) and from 91 to 117% for Cr(III).

Sampling and analysis of pesticides in ambient air.

Developments in the sampling and determination of pesticides in ambient air have been discussed and data on the occurrence of pesticides in atmosphere have been presented. Developments in active sampling methods were reviewed and the different materials used for trapping pesticides from gas and particulate phases were discussed. Likewise, the use and developments of passive air samplers were reviewed. This article pays special attention to the analysis of pesticides trapped from ambient air, and recapitulate the procedures for extraction, clean-up and determination of these substances. Improvements in sampling procedures, analytical methods and monitoring activities are necessary to advance the knowledge of occurrence of currently used pesticides in atmosphere and their impact over environment and humans.

On-line microwave oven digestion flame atomic absorption analysis of solid samples

Abstract A manifold has been developed for on-line microwave oven digestion and flame atomic absorption spectrometric (FAAS) determination of metallic elements in solid samples. The use of a closed flow system permits sample treatment before analysis by FAAS, the direct injection of slurries avoids a filtration step and the interconnection of two conventional rotary injection valves allows the rapid introduction of samples and standards. The determination of lead in sewage sludge was employed as a test system for the proposed on-line sample digestion manifold. The procedure has a limit of detection of 0.2 μg Pb g−1.

Determination of PAHs in airborne particles by accelerated solvent extraction and large-volume injection-gas chromatography-mass spectrometry

A sensitive and automated method is presented for the determination of polycyclic aromatic hydrocarbons (PAHs) in airborne particulate matter. The procedure includes extraction of PM10-bound PAHs by accelerated solvent extraction (ASE) followed by gel permeation chromatography (GPC) clean-up, and large-volume programmable temperature vaporizer (PTV-LV) injection coupled to GC-MS. The limit of detection (LOD) of the whole method, based on a signal-to-noise ratio (S/N) of 3:1, ranged from 0.26pgm(-3) to 3pgm(-3) when air volumes of 760m(3) are collected. The hexane-acetone mixture (1:1, v/v) gave the best recoveries when ASE parameters were fixed at 125 degrees C, 1500psi, and a total time of 10min. The recoveries for all PAHs tested ranged from 96% to 103%, rates similar to those obtained by the Soxhlet reference method. To improve the sensitivity, 70muL were injected. The PTV-LV injection settings were optimized using a statistical design of experiments, including a screening 2(4) full factorial design and a further central composite design. A sensitivity increase from 10 to 50 times was achieved as compared with the conventional 2muL splitless injection. The method was validated with the standard reference material SRM 1649a and applied to real PM10 samples from the monitoring network of the Regional Valencia Government (Spain). The analytical performance of the method shows that it is appropriate to monitor PAHs levels in ambient air according to European Union Directives. In addition, the method can be used when a high sensitivity is required.

The use of near-infrared spectrometry in the olive oil industry.

The enormous possibilities offered by near-infrared (NIR) spectroscopy for the (on/in/at-line) quality control process of olive fruits, pastes, and oils are summarized throughout this paper. Special attention has been paid to the combination of NIR and chemometric treatments for the on-line analysis of olive fruits and also for the quality parameters evaluation on olive oils and pastes which can enhance the production of a high quality olive oil and the selection of olive fruit with superior properties. The implementation of NIR sensors in olive mills with successful results has also been reviewed and the commercial olive fruit and oil analyzers highlighted.

On-line microwave-assisted digestion of solid samples for their flame atomic spectrometric analysis.

A new procedure has been developed for the on-line digestion of solids in a microwave oven. The direct injection in a water carrier flow of dispersions of solid samples in concentrated nitric acid, the merging of these slurries with 30% (v/v) H(2)O(2) and the microwave-assisted digestion in a Teflon coil of 100 cm permit a fast and quantitative extraction of Cu and Mn from different solid matrices, such as vegetables, powdered dietary products and sewage sludges. The development of an appropriate interphase, in which digested samples are cooled and degassified, previous to their introduction into the nebulizer of a flame atomic absorption spectrometer, makes possible the full automatization of the digestion and measurement steps of the elemental analysis of solids and it provides a sample frequency of 180 injections per hour. The developed procedure has also been applied for Pb and Zn determination in certified sewage sludge samples, with accurate results obtained for Pb but low results found for Zn.

Literature survey of the on-line preconcentration in flow-injection atomic spectrometric analysis

SummaryThe literature on the use of “on-line” preconcentration in flow injection atomic spectrometric analysis is reviewed, taking into account its application both in flame and electrothermal atomic absorption methods as well as in plasma emission spectrometry. The basis of the different preconcentration approaches, such as liquid-liquid extraction, column preconcentration and “on-line” precipitation are discussed. The literature survey reveals the analytical performance of the developed methodologies.