A GAS-SAMPLING GLOW-DISCHARGE COUPLED TO HYDRIDE GENERATION FOR THE ATOMIC SPECTROMETRIC DETERMINATION OF ARSENIC

A gas-sampling glow discharge (GSGD) has been coupled with a continuou s-flow hydride generator and optimized for the determination of As. Th e discharge characteristics of the source, operated at constant voltag e, and its sampling capabilities have been studied for helium, neon an d argon used as discharge gases. The evolved arsine, the accompanying hydrogen and the noble support gas were drawn into the discharge with an efficiency as high as 78%. Spatially resolved maps were obtained of the As I 228.8 nm line, the spectral background and the fill-gas line s, all as a function of the discharge pressure, in order to identify o ptimal working conditions. Under these conditions, noise amplitude spe ctra of analytical signals are completely white. Detection limits for As with helium (operated at 6.5 torr (1 torr = 133.332 Pa) and 650 V), with neon (operated at 2.5 torr and 750 V) and with argon (operated a t 1.5 torr and 550 V) are 54 ng/ml, 30 ng/ml and 20 ng/ml, respectivel y. The linear portions of calibration curves extended to 10 mug/ml in the argon discharge and to 2 mug/ml for neon and helium.