Trapping of hydride forming elements within miniature electrothermal devices: part I. investigation of collection of arsenic and selenium hydrides on a molybdenum foil strip

Abstract

The interaction of selenium and arsenic hydrides with surface of bare and modified (Pt, Ir and Rh) strips of the molybdenum foil was investigated by atomic absorption spectrometry employing miniature hydrogen diffusion flame as a simple atomizer and by radiotracer technique using 75Se-radionuclide as an indicator. In contrast to the recently reported data for tungsten atomizers, enhanced trapping was observed at the temperatures above 1000 °C, close to 1100–1200 °C, for the bare and modified molybdenum foil strips, irrespective of the analyte, and amount and type of the modifier deposited. When using a 75Se-radiotracer, the same selenium trapping efficiency of approximately 30% was found for the bare and rhodium-treated foils at the temperature of 1200 °C. Trapping isotherms of both analytes appeared to be very close to the linear fit even up to the upper limit of the analytical relevancy of 100 ng of an analyte, indicating a very high trapping capacity of the bare and modified surfaces. The influence of injection gas flow rate and capillary distance suggested that aerodynamic conditions of the injected gas near the molybdenum surface play significant role in trapping both analytes. The maximum trapping efficiency was reached for flow rates close to 60–70 ml min −1 and for a relatively short distance of 1–2 mm between the capillary orifice and the foil surface. Radiography experiments with 75Se-radiotracer showed that a major part of selenium was collected on a relatively small area, in the central part of the strip, opposite the orifice of the injection capillary. After trapping and vaporization steps, deposits of the selenium tracer were also found on the quartz tube wall of the trap chamber, close to the heated part of the strip.