Determination of pesticides in seaweeds by pressurized liquid extraction and programmed temperature vaporization-based large volume injection-gas chromatography-tandem mass spectrometry.

A rapid method for the simultaneous identification and quantification of pesticide residues in edible seaweed has been developed. Target analytes were three pyrethroid, a carbamate and two organophosphorus pesticides. The procedure consists of a pressurized liquid extraction (PLE) with integrated clean-up, followed by gas chromatography coupled to tandem mass spectrometry. Five PLE parameters were investigated using a screening design: temperature, static extraction time, number of cycles, percent of flush volume and quantitative composition of the n-hexane/ethyl acetate extraction solvent. The effect of the in-cell clean-up with Florisil and graphitized carbon black adsorbents was investigated using a Doehlert response surface design. Large volumes of sample extracts were injected using a programmed-temperature vaporizer (PTV-LVI) to improve both sensitivity and selectivity of measurements. Quantification was carried by the internal standard method with surrogate deuterated standards. The method showed excellent linearity (R2>0.999) and precision (relative standard deviation, RSD < or = 8%) for all compounds, with detection limits ranging from 0.3 pg g(-1) for chlorpyrifos-ethyl, to 3.0 pg g(-1) for carbaryl (23.1 pg g(-1) for deltamethrin). Recoveries in real seaweed samples were within the range 82-108%. The method was satisfactory validated for the analysis of wild and cultivated edible seaweeds. The presence of pyrethroid and organophosphorus pesticides in some of the samples was evidenced.

Development of a matrix solid-phase dispersion method for the screening of polybrominated diphenyl ethers and polychlorinated biphenyls in biota samples using gas chromatography with electron-capture detection.

A low cost method for the screening of six polybrominated diphenyl ethers (PBDEs) and seven polychlorinated biphenyls (PCBs) in biological samples containing up to 100% of fat is presented. Compounds are extracted from the sample and isolated from lipids using a matrix solid-phase dispersion (MSPD) cartridge and 20 ml of n-hexane as elution solvent. PBDEs and PCBs are fractionated on a second cartridge containing 2 g of a normal phase sorbent. The potential of neutral silica, Florisil and basic alumina to separate PBDEs and PCBs in two independent fractions has been evaluated. The best results were obtained using silica. PCBs are eluted, in a first fraction, using n-hexane. PBDEs are further recovered with n-hexane-dichloromethane. The applicability of the method for the screening of PBDEs and PCBs, in samples containing both groups of compounds, has been demonstrated using spiked, certified and real polluted samples from different biota materials. Globally, recoveries higher than 75% and quantification limits around 0.4 ng/g have been achieved using gas chromatography with electron-capture detection (GC-ECD).

Selective extraction of trace levels of polychlorinated and polybrominated contaminants by supercritical fluid-solid-phase microextraction and determination by gas chromatography/mass spectrometry. Application to aquaculture fish feed and cultured marine species.

The persistence, ubiquity, and toxicity of polyhalogenated compounds, together with their presence in fish feed, make it necessary to monitor these organic pollutants in the routine quality assurance programs of aquaculture activities, as this food chain is a source of these toxic compounds for human consumers. A new approach based on simultaneous supercritical fluid extraction-sample cleanup, followed by solid-phase microextraction-gas chromatography/mass spectrometry (SFE-SPME-GC/MS/MS) has been developed as an advantageous analytical tool for the determination of 15 organohalogenated compounds (including pesticides, polychlorinated and polybrominated biphenyls, and polybrominated diphenyl ethers) in aquaculture feed at very low levels. The influence of several parameters in the efficiency of the SPE/SPME combination was systematically investigated by chemometric approaches. In the optimal conditions, the developed procedure provides an excellent linearity, detection, and quantification limits (below 10 pg/g) for most of the analytes investigated, being at the same time advantageous in terms of rapidity, convenience, and avoiding the need of toxic organic solvents. The procedure was applied to the analysis of aquaculture feed and cultured marine species and tested for accuracy against IAEA 406 reference material.

Application of matrix solid-phase dispersion to the determination of polychlorinated biphenyls in fat by gas chromatography with electron-capture and mass spectrometric detection.

A one-step extraction-purification method for the determination of polychlorinated biphenyls (CBs) in fat samples was developed. Matrix solid-phase dispersion using different combinations of normal phase sorbents and elution solvents was evaluated, in terms of extraction yield and lipids removal efficiency, for the isolation of CBs from butter, chicken and beef fat. Under optimal conditions, 0.5 g of sample was dried with anhydrous sodium sulphate, dispersed on 1.5 g of Florisil and transferred to the top of a polyethylene solid-phase extraction cartridge which already contain 5 g of Florisil. Non-coplanar CBs were quantitatively eluted with 15 ml of n-hexane. The lipid percentage in this extract remained below 0.06% of the sample mass. As coplanar congeners show a higher affinity for Florisil, 20 ml of hexane-dichloromethane (90:10) were necessary for the quantitative recovery of coplanar and non-coplanar CBs. The potential of the procedure to fractionate non-coplanar and coplanar congeners is discussed. After extract evaporation to 0.2 ml, quantification limits of 0.4 ng of each CB per g of fat were achieved, using gas chromatography with tandem MS or electron-capture detection (ECD).

Selective determination of polychlorinated biphenyls in waste oils using liquid-liquid partition followed by headspace solid-phase microextraction and gas chromatography with atomic emission detection.

A procedure for the determination of the total content of polychlorinated biphenyls (PCBs) in industrial oil samples using gas chromatography coupled to atomic emission detection (GC-AED) is presented. Analytes were extracted from the samples using dimethylsulfoxide (DMSO), this extract was diluted with water, and PCBs were concentrated on a PDMS-DVB solid-phase microextraction (SPME) fibre using the headspace (HS) mode. Fibres were thermally desorbed for 3 min in the splitless injection port of the GC-AED system. Influence of liquid-liquid extraction conditions on the performance of the analytical procedure is presented and the need of a sample oxidation step, previous to the extraction of the PCBs with DMSO, discussed. Working under optimal conditions, quantification limits from 0.5 to 1 microg/g (total PCBs content) were obtained for several Aroclor mixtures in transformer oil samples. The repeatability of the whole sample preparation procedure (liquid-liquid partition followed by headspace SPME and GC-AED determination) ranged from 4 to 7%.

Optimization of a microwave-assisted derivatization-extraction procedure for the determination of chlorophenols in ash samples.

A procedure for the determination of 17 chlorophenolic compounds in ash samples obtained from the incineration of waste materials is described. Analytes were simultaneously derivatized with acetic anhydride in presence of triethylamine (TEA), and extracted from the sample in a mixture of n-hexane acetone using a microwave system equipped with closed extraction vessels. Influence of five experimental parameters (volume of TEA and acetic anhydride, extraction time and temperature, as well as the volume of n-hexane acetone) on the yield of the derivatization-extraction procedure was systematically studied using a uniform experimental design at four levels, followed by a conventional factorial design at two levels. Under optimal extraction conditions, recoveries from 72 to 94% were obtained for a spiked ash sample with a carbon content of 8.7%. Quantification limits of the proposed procedure ranged from 2 to 5 ng/g using GC-MS as detection technique. The proposed method was applied to the determination of chlorophenols in three ash samples obtained from different incineration plants. Total chlorophenol contents of 423 and 135 ng/g were found in two of these samples.

Optimization of a microwave-assisted extraction method for the analysis of polychlorinated biphenyls in ash samples.

An alternative method for the extraction of polychlorinated biphenyls (PCBs) in ash samples, which is less time and solvent consuming than Soxhlet extraction, is presented. A study was carried out to evaluate the possibilities of microwave-assisted extraction (MAE) to determine exactly which parameters affect the efficiency of the process, since direct extrapolation of extraction conditions for PCBs in other solid matrices, failed when applied to coplanar congeners in ash samples. Influence of the organic solvent on the yield of the extraction was first evaluated using two ash samples with different percentages of carbon. Once the extraction solvent was fixed, the effects of solvent volume, extraction temperature and extraction time were investigated using an experimental design. It was found that the volume of organic solvent played a more important role in the extraction efficiency than the other factors. In the optimal conditions microwave extractions were performed at 110 degrees C. for 10 min and using 30 ml of toluene. Recoveries higher than 80% were obtained for all the highly chlorinated congeners. including coplanar species, in a spiked ash sample containing a relatively high concentration of carbon. The proposed method was also applied to the determination of PCBs in a reference material of urban dust. Recoveries were similar to those obtained for spiked ash samples.

Determination of polychlorinated biphenyl compounds in indoor air samples.

A simple procedure for the determination of six non-coplanar polychlorinated biphenyls (PCBs) in medium volumes of indoor air is described. Samples are forced at 6 m3/h through a device consisting of a quartz filter connected to the end of a conventional solid-phase extraction cartridge containing 60 mg of functionalized styrene-divinylbenzene. PCBs retained on the sorbent are directly eluted with 2 ml of hexane. Those associated to airborne particulate matter are microwave extracted in 10 min using 15 ml hexane-acetone (1:1). The proposed procedure is favorably compared to the use of polyurethane cylinders for the concentration of PCBs in terms of solvent consumption and rapidity of the desorption step. Furthermore, the functionalized sorbent showed higher breakthrough volumes than Amberlite XAD-2 for PCBs in gas phase. Quantification limits between 2 and 40 pg/m3 were obtained for six PCBs (from di- to heptachlorobiphenyls) using GC-electron-capture detection.

Speciation of organomercurials in biological and environmental samples by gas chromatography with microwave-induced plasma atomic emission detection.

The applicability of a commercial microwave-induced plasma atomic emission detector with capillary gas chromatography for mercury speciation in environmental samples was examined. The chromatographic conditions were optimized in order to obtain an adequate resolution of the methylmercury peak vs. interfering carbon signals. Under the proposed operational conditions, the detection limit (signal-to-noise ratio = 3) was 1.2 pg with a linear range of 1-40 ng ml-1 (as methylmercury in samples). Certified reference material (DORM-1) was used to evaluate the accuracy. The results of the proposed procedure were compared with those obtained by means of the usual GC method with electron-capture detection.

A study of behavioural groupings of polyphenolic species in "fino" sherry wine. Evolution during vinification and mechanical treatment of the grape.

The different groups and/or classes among phenolic acids and aldehydes identified during the elaboration process of "fino" sherry wine have been studied. The study was carried out using different processes during the elaboration of the wine and we have attempted to establish whether the different treatments of the grape affect these groupings. The study was undertaken by means of cluster and multifactorial analysis on the data obtained by the quantitative determination of phenolic acids and aldehydes during vinification and in experiments carried out on the grape under different mechanical treatments. The analysis of phenolic acids and aldehydes was done with HPLC, using a C-18 mu-Bondapak and a stepwise composite gradient. The samples were previously extracted with ethylic ether.