E. Morales

A comparison between ICP-MS and AFS detection for arsenic speciation in environmental samples

Performances of two atomic detectors, Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Atomic Fluorescence Spectrometry (AFS) have been compared for arsenic speciation in environmental samples. Instrumental couplings, based on the use of high performance liquid chromatography (HPLC), hydride generation (HG), and the two atomic detectors were used for the speciation of arsenite, arsenate, dimethylarsinic acid and monomethylarsonic acid. Optionally, arsenobetaine was also determined using on-line ultraviolet (UV) photooxidation. The detection limits ranging from 0.1 to 0.3 mug l(-1) (as As) and the precision >10% RSD obtained with HPLC-(UV)-HG-AFS were comparable with those obtained with HPLC-(UV)-HG-ICP-MS. Both instrumental coupling were applied to the NRCC-TORT-1 and several environmental samples, such as seawater, freshwater, sediments, bivalves and bird eggs, taken from two areas with different degrees of pollution. No influence of the sample matrix was observed on the results using external calibration and standard additions methods, for both coupled techniques.

Determination of polychlorinated biphenyls in biota samples using simultaneous pressurized liquid extraction and purification

In order to reduce time and cost of analysis, a new pressurised liquid extraction method that automatically and rapidly achieves quantitative and selective (i.e., lipid-free) extraction of polychlorinated biphenyls (PCBs) in biota tissues was optimized. It consists of on-line clean-up by inclusion of sorbents in the extraction cell. The freeze-dried sample is dispersed with Florisil and loaded in the extraction cell containing an extra amount of Florisil. The extraction is performed under mild conditions using 55 ml of a dichloromethane-pentane (15:85) mixture, a temperature of 40 degrees C, a static extraction time of 10 min and two extraction cycles. The Florisil retains coextracted lipids from the matrix, and the extract, after pre-concentration, is clean enough for direct injection into GC-MS and GC-electron-capture detection (ECD). Quantitative recoveries (from 90 to 106%) are obtained for both native and spiked PCB congeners in samples with a high lipidic content (up to 42% dry mass, in spoonbill eggs). The reproducibility of replicate extractions was better than 11% relative standard deviation. Method detection limits were in the ranges of 0.001-0.004 and 0.002-0.07 ng g(-1) dry mass for GC-ECD and GC-MS-MS, respectively. The method was validated using the standard reference material SRM 2974 (a mussel tissue) from the US National Institute of Standards and Technology, compared to Soxhlet and matrix solid-phase dispersion extraction methods, and used to evaluate the contamination by PCBs in bivalves from South of Spain.

Stability of chemical species in environmental matrices

The stability of chemical species in environmental samples is a critical factor during storage, owing to the interconversion and degradation processes which can occur in species characterisation. The preservation and stabilisation of these chemical species in the time interval between sampling and analysis is a difficult task and several studies have been developed to improve the quality of this aspect of speciation analysis. The Measurement and Testing Programme (formerly BCR) has undertaken projects focused on a variety of species (e.g. Sn, Se, As, Sb, Hg, Pb, Cr), which have been complemented by the studies of other authors. The procedures proposed are reviewed in detail and the influence of critical operational parameters for species stability, such as pH, temperature, light and the container material is considered. The problems are not yet completely solved, especially for complex solid matrices such as soils, sediments and biological tissues.

Comparison of biota sample pretreatments for arsenicspeciation with coupled HPLC-HG-ICP-MS

Soxhlet extraction has been compared to sonication and microwave assisted extraction of arsenite, arsenate, dimethylarsenic, monomethylarsenic and arsenobetaine from biota samples (oyster, cockle, mussel and fresh water alga) and Certified Reference Materials TORT-1 and CRM 627, using methanol and methanol–water mixtures. A clean-up procedure using hexane partitioning was compared to the use of 0.45 μm filter membranes, ultrafiltration (10 kDa) and C-18 cartridges. Measurements were carried out using coupled HPLC-(UV)-HG-ICP-MS. The best results were obtained for Soxhlet extraction (150 ml of a (1∶1) methanol–water mixture for 16 h) compared to both sonication (20 ml of methanol or methanol–water mixtures (1∶3), (1∶1) and (3∶1) during 20 min) and microwave (20 ml of methanol or methanol–water mixtures (1∶3), (1∶1) and (3∶1) during 10 min at 150 W). Hexane partitioning was found to be superior to the other clean-up procedures. Recoveries higher than 71% were obtained depending on the type of sample. An unknown compound was found to be the main arsenic species in the marine samples.

Sample treatment in chromatography-based speciation of organometallic pollutants

Speciation analysis is nowadays performed routinely in many laboratories to control the quality of the environment, food and health. Chemical speciation analyses generally include the study of different oxidation state of elements or individual organometallic compounds. The determination of the different chemical forms of elements is still an analytical challenge, since they are often unstable and concentrations in different matrices of interest are in the microg l(-1) or even in the ng l(-1) range (e.g., estuarine waters) or ng g(-1) in sediments and biological tissues. For this reason, sensitive and selective analytical atomic techniques are being used as available detectors for speciation, generally coupled with chromatography for the time-resolved introduction of analytes into the atomic spectrometer. The complexity of these instrumental couplings has a straightforward consequence on the duration of the analysis, but sample preparation to separate and transfer the chemical species present in the sample into a solution to be accepted readily by a chromatographic column is the more critical step of total analysis, and demands considerable operator skills and time cost. Traditionally, liquid-liquid extraction has been employed for sample treatment with serious disadvantages, such as consumption, disposal and long-term exposure to organic solvent. In addition, they are usually cumbersome and time-consuming. Therefore, the introduction of new reagents such as sodium tetraethylborate for the simultaneous derivatization of several elements has been proposed. Other possibilities are based in the implementation of techniques for efficient and accelerated isolation of species from the sample matrix. This is the case for microwave-assisted extraction, solid-phase extraction and microextraction, supercritical fluid extraction or pressurized liquid extraction, which offer new possibilities in species treatment, and the advantages of a drastic reduction of the extraction time and the embodiment into on-line flow analysis systems. This new generation of treatment techniques constitutes a good choice as fast extraction methods for feasible species-selective analysis of organometallic compounds under the picogram level, that can be used for national regulatory agencies, governmental and industrial quality control laboratories, and consequently, for manufacturers of analytical instrumentation.

Comparison of the feasibility of three extraction procedures for trace metal partitioning in sediments from south-west Spain

The feasibility of three sequential extraction schemes (a modification of the Tessier procedure, the scheme proposed by Meguellati and the protocol designed by BCR (now called the Standards, Measurements and Testing Programme, M&T) have been compared to study the distribution of As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn in sediment samples. The comparison has been performed by analyzing Certified Reference Material (CRM-601), a test material (S-12) and seven sediments from the Odiel Marshes Natural Park (located at the Atlantic coast of southern Spain). Samples were classified as sandy (with low iron oxide and organic matter contents) and clay-silty (with high iron oxide and organic matter contents) sediments. A higher metal mobility, especially under reducing conditions, was more properly assessed using the modified Tessier scheme compared to both the BCR and Meguellati procedures, these two later presenting comparative results for the reducible and residual phases. Significant Hg losses were found using the BCR procedure but the quantification of the acid phase for Cd, Cr and Ni was more reliable than that obtained with the modified Tessier and Meguellati schemes.

Selectivity assessment of a sequential extraction procedure for metal mobility characterization using model phases

This study considers the selectivity of the extractants used in a sequential extraction scheme for metals mobility assessment by analyzing individual mineral phases previously coprecipitated or sorbed with trace metals. The scheme evaluated was a modification of the Tessier et al. [A. Tessier, P.G.C. Campbell, M. Bisson, Anal. Chem. 51 (1979) 844] sequential procedure proposed by the authors. The phases studied were calcite, amorphous iron oxide, hausmannite, humic acid, kaolinite and illite. Selective extractions were obtained for As, Cr, Cu, Ni, Pb and Zn in metal-coprecipitated phases whereas NH(2)OH-HCl was not selective for the extraction of Hg and Cd coprecipitated in hausmannite and amorphous iron oxide, respectively. Otherwise, Cd, Hg, Ni and Zn sorbed on the different phases were released with MgCl(2) and NaOAc/HOAc, but stronger reagents were needed to release As, Cr, Cu and Pb.

Spatial distribution of butyltin and phenyltin compounds on the Huelva Coast (Southwest Spain)

Six organotin species -tributyltin (TBT), dibutyltin (DBT), monobutyltin (MBT), triphenyltin (TPT), diphenyltin (DPT) and monophenyltin (MPT)- have been determined in seawater and sediments collected from some representative enclosed areas of the southwest Spain. No phenyltin species were found in waters showing the absence of recent inputs of these species. However, butyltin species were present in all the stations along the Huelva coast. The highest TBT levels were found in sediments (up to 195 ng g−1 as Sn, dry weight basis) and seawater (up to 100 ng L−1) in harbours and marinas, closely related with boating activity and decreasing according to the distance from the potential sources. Results make possible to establish conclusions about the critical ecological consequences of organotin presence in this area, where shell-fish farms, fishery activity and migrating birds might be at risk. Different TBT degradation rates were found in sediments collected in winter (Cadiz coast) and in summer (Huelva coast).

Column-switching system for selenium speciation by coupling reversed-phase and ion-exchange high-performance liquid chromatography with microwave-assisted digestion–hydride generation–atomic fluorescence spectrometry

Speciation of selenocysteine (SeCys), selenomethionine (SeMet), selenoethionine (SeET), selenite (Se(IV)) and selenate (Se(VI)) has been accomplished using high-performance liquid chromatography, with the aid of an anion exchange column and a reversed-phase column, both connected through a six-port switching valve. On-line microwave-assisted digestion and hydride generation steps were performed prior to the atomic fluorescence detection. The elution of the seleno amino acids was accomplished in the reversed-phased column using water as mobile phase. Selenite and selenate were separated in the anion exchange column, using gradient elution with an acetate buffer. The separation of the five selenium compounds took place in 15 min. The detection limits obtained ranged between 0.6 and 0.9 microg l(-1). Values of r>0.998 were obtained for linear fit graphs. A commercial available urine sample was analyzed, in which SeCys and Se(IV) were quantified.

Uptake and elimination of tributyltin in clams, Venerupis decussata

Abstract This paper considers the use of Venerupis decussata as a bioindicator of tributyltin (TBT) exposure using kinetic approaches. Clams, V. decussata , were exposed in a daily renewal protocol to different TBTCl concentrations: 0.004, 0.0814, 0.242, 0.740 and 2.47 μg L −1 . The time course of accumulation in the whole soft tissues was determined for a maximum exposure period of 60 days. In 2.47 μg L −1 a steady state was reached within 30 days and in lower exposure concentrations within 40 days. Bioconcentration factors (BCF) for TBT in clams ranged between 10 000 and 40 000. TBT data during the accumulation experiments were fitted to the one-order kinetic model and kinetic parameters, uptake and depuration rate constants, were calculated. Depuration was studied in a flow through system for a period of 100 days. TBT data during the depuration experiments were fitted to both one-compartment and two-compartment models. Using a one-compartment model, half-life values for TBT were calculated and ranged between 11 and 36 days, increasing for lower concentrations.