DIRECT-DETECTION OF VACUUM-ULTRAVIOLET RADIATION FOR NONMETAL DETERMINATIONS WITH A HELIUM MICROWAVE-INDUCED PLASMA

A study of the determination of metals, nonmetals, and metalloids (F, Cl, Br, I, S, P, Se, As, Sb, and Pb) in the vacuum-ultraviolet spectral region with a kilowatt-plus helium microwave-induced plasma is presented. A spectrometer system similar to that used for far-ultraviolet optical sampling with an inductively coupled plasma was designed and implemented. This arrangement was produced by using an optical sampler to couple the plasma discharge with a helium-purged monochromator. Monitoring was performed at wavelengths less than 200 nm with no N2 or O2 in the optical path. Helium was chosen as the purge gas because it is transparent in the wavelength region of interest (>58 nm). Sample introduction was accomplished with ultrasonic nebulization. Limits of detection, linear ranges, and matrix effects caused by group IA and IIA elements were studied. Analytical calibration plots were linear over a range of 2-3 orders of magnitude. Detection limits ranged from 0.06 mug/mL for sulfur to 5 mug/mL for selenium.