1999 Volume 85 Issue 2 Pages 97-101
An annular-shaped high power nitrogen microwave induced plasma (N2-MIP) produced at atmospheric pressure by an Okamoto cavity in a surface wave mode has been used as a new and efficient excitation source for atomic emission spectrometry (AES). The results show that this kind of MIP source is more stable than conventional low power MIPs and remarkably tolerant to direct and continuous introduction of wet aerosols and molecular gases such as hydrogen, oxygen, air and gaseous hydrides because of its high input microwave power. Under the optimized experimental conditions, the best attainable detection limits at As(I) 228.812 and Se(I) 196.026 nm by use of N2-MIP-AES coupled with hydride generation technique were 2.99 ng As/ml and 0.86 ng Se/ml with a linear dynamic ranges of 5 to 10, 000 ng As/ml and 1 to 5, 000 ng Se/ml. The presence of several diverse elements has been found to cause more or less a depressing interference with the determination of arsenic and selenium by the present technique. Of the several pre-reductants potassium iodide has been found to be the most preferable to reduce As(V) to As(III) prior to hydride generation for the determination of total arsenic, i.e., As(III)+As(V). To the contrary, the heating of sample solutions, previously acidified in 5 M with hydrochloric acid, at 80°C for 20 min was the best way to pre-reduce Se(VI) to Se(IV) before hydride generation for the determination of total selenium, i.e., Se(IV)+Se(VI). The proposed method was applied to the determination of low concentrations of arsenic and selenium in carbon steels and stainless steels, respectively. The results obtained by this method were in good agreement with the certified values.
