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.

Optimisation of the coagulation-flocculation process of raw water by optimal design method.

In the present paper, a systematic study of the influence of raw water quality and operating conditions on the effectiveness of the coagulation-flocculation process using aluminium sulphate (AS) is presented. The influence of raw water composition is studied at two levels, fractional factorial designs and a Doehlert uniform shell design to determine the influence of the operating conditions. The analysis of the experimental responses (residual turbidity and minimally AS dose are denoted as (Tu(m)) and (AS(m)), respectively) shows that the parameters which have the greatest influence change depending on the response. It is not always possible, for a given water composition, to obtain simultaneously low residual turbidity and minimally AS dose. However, under the conditions of this study, the search for a criterion of optimisation must bear the minimisation of residual turbidity, because it remains the principal criterion of effectiveness of the process, even, if in a few cases, it results in an increase in the cost of treatment.

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.