Add time:09/24/2019         Source:sciencedirect.com

Techniques for the determination of trace element compounds at ppb1 and ppm levels (in contrast to the determination of the total element concentration) are a prerequisite for the study of the transformations of trace elements in biological systems and the interactions of trace element compounds with biologically important molecules. Two automated high-pressure liquid chromatography (HPLC) systems with element-specific detectors, capable of detecting, identifying and quantitating trace element compounds were developed independently in our laboratories. One of the detectors consists of a Perkin-Elmer graphite furnace atomic absorption spectrometer (GFAA) and a specially adapted autosampler, whereas a Hitachi-Zeeman GFAA, a sample valve, an injector and associated electronics to control the analysis sequence comprise the components of the other detector. The capability of these systems to speciate trace element compounds is demonstrated using arsenite, arsenate, METHYLARSONIC ACID (cas 124-58-3) (MAA) and dimethylarsinic acid (DMAA) as examples. Arsenite, MAA and DMAA were successfully separated and quantitatively determined on a strong anion-exchange column with an aqueous acetate buffer as mobile phase. Arsenite, DMAA and arsenate can be speciated with a strong cation-exchange column using an aqueous solution of ammonium acetate as mobile phase. All four arsenic compounds can be separated on a C18 reversed-phase column with methanol-water mixtures saturated with tetraheptylammonium nitrate. These compounds can be identified and quantified in solutions containing 10–20 ppb arsenic. Sample sizes required for GFAA analysis vary between 20 and 100 μl. The separation schemes developed for the four arsenic compounds were used to speciate these compounds in 5 ppb even in rather complex matrices employing a SAX column. Arsenate and arsenite can be determined using a SCX column provided methylarsonate is not present. All four compounds can be separated and quantitated on a C18 reversed-phase column. These separation schemes are applicable to the determination of arsenic compounds in soil extracts and drinking water samples. The separations reported in this paper very likely can be improved by application of columns tailored to arsenic compounds. As an example of column materials development the preparation of reversed-phase cation- and anion-exchange resins is mentioned. These columns were used to separate heterocyclic nitrogen bases and ribonucleoside phosphates12 and should be applicable to the separation of arsenic compounds. Recently the use of a proprietary special anion-exchange column for the separation of arsenic compounds was reported13. Improved column design will make the HPLC-GFAA technique even better suited for the speciation of trace element compounds in a variety of matrices. The work with arsenic compounds clearly shows the great potential of these systems in the area of environmental trace element chemistry, in the field of physiological chemistry and in trace-element related nutritional studies.

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