Determination of Ultratrace Selenium and Arsenic at Parts-Per-Trillion Levels in Environmental and Biological Samples by Atomic Fluorescence Spectrometry with Flow Injection Hydride Generation Technique

摘要

Hydride vapor generation atomic absorption spectrometry (AAS) is a preferred method for determination of hydride-forming elements such as selenium and arsenic, particularly at ultratrace concentration levels. In this applied research, the hydride vapor generator-coupled atomic fluorescence spectroscopic system has been used to replace the atomic absorption spectroscopic detector, which is used in the ordinary hydride generation technique. Also, the successful analysis of samples using the flow injection hydride generation system (FIA-Hydride) is combined with the atomic fluorescence spectrometer. For better sensitivity, membrane dryers have been used that use a hygroscopic, ion-exchange membrane in a continuous drying process between hydride generator (separator) and atomic fluorescence detector to selectively remove water vapor from mixed hydride gas streams. The effects of carrier gas flow rate, different acids, and acid concentrations on sensitivity have been tested to select the best conditions. More than 200 times enhancement of sensitivity has been shown in the hydride generation atomic fluorescence spectroscopy system (Hydride-AFS). The instrument detection limit (IDL) and method detection limit (MDL), which takes into account sample preparation process effects, were determined. Detection levels of a few parts per trillion without a preconcentration stage and clean room are achieved for actual samples of selenium and arsenic. The widest linear dynamic range is about four orders of magnitude: between 0.025 and 250 ng/ml of selenium and arsenic. The present method is applied to determining selenium and arsenic in environmental samples such as surface water, soil, and fish tissue. The sediment standard (MASS-2) and water and tissue sample spike have been tested by the present method with good recoveries. Also, the analytical results for selenium and arsenic in surface water, sediment, and fish tissue obtained by the FIA-Hydried-AFS method and Hydride-AAS method are compared. As is clearly shown in these results, the present new FIA-Hydride-AFS method not only provides good agreement with the values obtained by the ordinary Hydride-AAS method, but the performance of this system suggests that it will be effective for the analysis of arsenic and selenium at ultratrace levels.