Application of dc voltage modulation technique to the determination of phosphorous and sulfur in steel samples in glow discharge optical emission spectrometry

An applied voltage modulation technique was applied to the high-sensitivity determination of phosphorous and sulfur in steel samples in glow discharge optical emission spectrometry. Emission signals from the glow discharge plasma were modulated by a cyclic variation of the discharge voltage so that only the desired signals could be detected without any noises with a DSP lock-in amplifier. The relative lock-in signals from sputtered species were enhanced compared to those of gas species. The PI 177.49-nm, and the SI 180.73-nm and SI 182.72-nm lines, were selected as the analytical lines. The limit of determination for the PI 177.49-nm line was estimated to be 1.0x10(-3) mass% P.