Design and characterization of a direct current glow discharge lamp for analytical applications

Abstract

This paper describes a compact, small volume direct current glow discharge lamp operating at low wattage for atomic emission spectrometric analysis and its process optimization for copper and brass solid samples. The design aspects, fundamental characteristics and analytical performance are described in detail. The discharge is observed end-on, with water-cooled cathode surface parallel to the spectroscopic entrance slit. The anode diameter is 7 mm and the minimum sample diameter required is 20 mm. The sample is located outside the lamp for easy access and interchangeability. The lamp is powered by a dc power supply capable of delivering 300 mA (max.) and 1500 V. The studies of fundamental characteristics include the current–voltage relationship and their dependence on pressure and the emission intensity of copper spectral line (324.7 nm). The studies were made in the pressure range of 2–7 mbar. Long-term stability of optical emission spectra was also recorded to be within ±0.75%. The performance of the lamp is quite linear in the pressure range 3.5–7 mbar at an applied voltage of about 450 V.