EVALUATION OF HIGH-PRESSURE MICROWAVE DIGESTION METHODS FOR HYDRIDE GENERATION ATOMIC-ABSORPTION SPECTROMETRIC DETERMINATION OF TOTAL SELENIUM AND ARSENIC IN SEDIMENT

Five closed-vessel microwave digestion methods were compared for the a ccurate determination of arsenic and selenium in NIST SRM 1645 River S ediment by flow-injection hydride-generation atomic absorption spectro metric methods. The digestion methods using five different acid mixtur es (HNO3/H2SO4, HNO3/HClO4, HNO3/HCl, HNO3/HCl/HF, HNO3/H2SO4/HClO4) w ere all found to be reliable for the determination of the analytes. Ta king into consideration the safety and suitability for the analysis of other metals, the methods based on the use of aqua regia are recommen ded for closed vessel microwave digestion with pressure control. Using the quick digestion program, the presence of up to 10% organic conten t in soil samples did not adversely affect the closed vessel digestion and did not cause the loss of volatile analytes. After digestion, ope ning the vessel under an inner pressure of below 345 kPa (50 psi) had no effect on the accuracy of the results. The recommended digestion me thods (HNO3/HCl and HNO3/HCl/HF) for the reliable determination of ars enic and selenium in different sediment samples were demonstrated. The calculated detection limits (3 sigma(B)) were less than 0.030 mu g/g and 0.033 mu g/g for arsenic and selenium, respectively. All analytica l results for arsenic and selenium in SRM 1645 River sediment, NRCC BC SS-1 Marine Sediment and NIES CRM Pond Sediment were within or near th e certified and reported ranges, with the exception of selenium in NIE S CRM No. 2 Pond Sediment.