In situ trapping of selenium hydride in rhodium-coated tungsten coil electrothermal atomic absorption spectrometry

Abstract

A flow injection hydride generation manifold was coupled to a tungsten coil electrothermal atomizer for in situ collection of selenium. This strategy exploits selenium hydride trapping onto a double-layer coiled tungsten filament coated with rhodium. The hydride flows through a capillary quartz tube (20 mm long × 1.3 mm od × 0.5 mm id) positioned 1 mm from the modified tungsten coil surface. The capillary can be either inserted in the tip of the autosampler arm by replacing the last section of the PTFE sample delivery tube, or can be fixed in a silicone stopper. Signal stability and repeatability were observed over 300 atomization cycles using 300 µg Rh thermally reduced over the tungsten coil surface. The coil lifetime was extended to at least 2000 firings at 2300 °C. An enrichment factor of 200 was obtained for selenium after 60 s of hydride trapping for a sample flowing at 2.5 ml min−1. The detection limit, based on three times the standard deviation of the blank, was 50 ng l−1 Se with a sample throughput of 40 h−1. Method accuracy was evaluated by analysing ordinary mineral water using the proposed method and hydride generation atomic fluorescence spectrometry and water reference materials from the National Institute of Standards and Technology (SRM 1640 Trace Elements in Natural Water) and from High-purity Standards (Trace Metals in Drinking Water). No statistical differences were found between the values encountered by both techniques and the certified values by applying a t-test at the 95% confidence level.