Optimisation of alachlor solid-phase microextraction from water samples using experimental design

We have tested screening and response surface experimental designs to optimise the solid-phase microextraction (SPME) of the widely used herbicide alachlor. Extraction time and sample volume were the only statistically significant factors from those studied. In the final optimised conditions the procedure was applied to the SPME-HPLC analysis of alachlor in spiked water samples with excellent figures of merit.     

Preparation of VaM2−aO4 (M=Nb,Ta; 1>-a>-0.2) with different oxygen contents

This paper describes the thermal behaviour of various oxides of pentavalent V and Nb or Ta in different dynamic hydrogen atmospheres. Previous studies of the phases obtained by heating mixtures of V₂O₅ and M₂O₅ (M=Nb, Ta) in air lead to (i) preparation of VTaO₅ from both oxides for the first time, (ii) proof of the existence of the solid-solutions VM _m O_5/2(m+1), and (iii) proof that the materials described as NbVO₅ and β-TaVO₅ are really mixtures of VM₉O₂₅ and V₂O₅. Reduction of VMO₅ gives monophasic rutile-type VMO₄ from 650°C. Reduction VM₂O_7.5, V₃M₁₇O₅₀ and VM₉O₂₅ at 1000°C leads to monophase non-stoichiometric V_aM_2?aO_y only forM=Nb.     

Studies on organo-mercury compounds speciation

Four studies on organo-mercury compounds speciation carried out in the analytical chemistry laboratory of the University of Santiago are briefly described and discussed. Search for new methods of separation based on liquid chromatography as well as quality control and application studies have been started and the results obtained up to the end of 1990 are presented.     

Optimization of the matrix solid-phase dispersion sample preparation procedure for analysis of polycyclic aromatic hydrocarbons in soils: comparison with microwave-assisted extraction

A fast and simple preparation procedure based on the matrix solid-phase dispersion (MSPD) technique is proposed for the first time for the isolation of 16 polycyclic aromatic hydrocarbons (PAHs) from soil samples. Naphthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[e]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene, benzo[g,h,i]perylene, and indeno[1,2,3-c,d]pyrene were considered in the study. Extraction and clean-up of samples were carried out in a single step. The main parameters that affect extraction yield, such as dispersant, type and amount of additives, clean-up co-sorbent and extractive solvent were evaluated and optimized. The addition of an alkali solution in MSPD was required to provide quantitative recoveries. Analytical determinations were carried out by high performance liquid chromatography (HPLC) with fluorescence detection. Quantification limits (between 0.01 and 0.6 ng g(-1) dry mass) were well below the regulatory limits for all the compounds considered. The extraction yields for the different compounds obtained by MSPD were compared with the yields obtained by microwave-assisted extraction (MAE). To test the accuracy of the MSPD technique, the optimized methodology was applied to the analysis of standard reference material BCR-524 (contaminated industrial soil), with excellent results.     

Optimization of a dispersive liquid-liquid microextraction method for the analysis of benzotriazoles and benzothiazoles in water samples

A simple and rapid dispersive liquid–liquid microextraction method has been developed for the determination of 11 benzotriazoles and benzothiazoles in water samples. Tri-n-butylphosphate (TBP) was used as extractant, thus avoiding the use of toxic water-immiscible chlorinated solvents. The influence of several variables (e.g., type and volume of dispersant and extraction solvents, sample pH, ionic strength, etc.) on the performance of the sample preparation step was systematically evaluated. Analytical determinations were carried out by high-performance liquid chromatography with fluorescence and UV detection and liquid chromatography–electrospray ionization-tandem mass spectrometry. The optimized method exhibited a good precision level with relative standard deviation values between 3.7% and 8.4%. Extraction yields ranging from 67% to 97% were obtained for all of these considered compounds. Finally, the proposed method was successfully applied to the analysis of benzotriazoles and benzothiazoles in real water samples (tap, river, industrial waters, and treated and raw wastewaters).