EXTRACTION TECHNIQUES FOR TRACE ELEMENT DETERMINATIONS OF BIOLOGICAL AND ENVIRONMENTAL SAMPLES INCLUDING ELEMENTAL SPECIATION OF LOBSTER USING INDUCTIVELY COUPLED PLASMA - MASS SPECTROMETRY

Adequate identification and quantification of elemental species in the environment are necessary to completely assess their potential toxicity. Inductively coupled plasma - mass spectrometry (ICP - MS) coupled to chromatographic separation is a widely used, highly sensitive detector. For samples to be analyzed by ICP - MS, they must first be extracted into a solution capable of being nebulized into the ICP. A variety of extraction procedures were evaluated for the extraction of arsenic and other analytes from lobster tissue samples using ICP - MS detection. Room temperature mixing, sonication, soxhlet, microwave assisted, supercritical carbon dioxide and subcritical water extractions were evaluated for a variety of solvent systems and optimum conditions determined using a partially defatted Lobster Hepatopancreas marine reference material (TORT-2, National Research Council of Canada). Microwave assisted extraction (MAE) yielded comparable or improved recoveries for all of the analytes monitored and proved to be the mildest, fastest, least complicated and most reproducible extraction technique. MAE at 75 °C for 2 minutes exposure time yielded quantitative recovery of arsenic from TORT-2 and lobster tissue samples purchased from a local restaurant A novel gradient anion exchange chromatographic technique was developed that allows the speciation of arsenobetaine (AB), arsenocholine (AC), arsenite (As III), arsenate (As V), monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) in ~ 27 minutes using ammonium carbonate buffer. Low detection limits, excellent long-term stability and baseline resolution of all of the arsenic species evaluated were achieved when the ratio of AC:AB was less than ~ 12.5:50. This technique was successfully applied to TORT-2 and lobster tissue samples. AB was the major arsenic species identified. AC, DMAA, AS V and unknown peaks, possibly arsenosugars, were also found. Methanol and isopropanol were evaluated as extraction solvents for a variety of analytes and samples using microwave assisted extraction and found to be relatively equivalent. Increased exposure time and temperature typically resulted in higher recoveries. The use of ammonium pyrrolidine dithiocarbamate and ethylenediamine tetraacetic acid as chelating agents also improved the extraction efficiency of some analytes. Recoveries were found to generally show some dependence upon the analyte of interest and the sample matrix.