Atomic fluorescence in a pulsed hollow cathode discharge with a copper vapor pumped dye laser

Abstract

Application of a pulsed glow discharge as an atomizer for atomic fluorescence spectroscopy with a copper vapor laser pumped dye laser excitation source was investigated. The discharge system was synchronously pulsed with the laser to provide a low noise background and the low pressure, inert gas atmosphere contributed to an almost ideal environment for fluorescence measurement. The high repetition rate of the copper vapor laser (6000 Hz) improved the detection efficiency over lower repetition rate laser systems. Disposable graphite cup electrodes were used as demountable hollow cathodes for measurement of aqueous samples. The samples were injected into the cathode cups and dried using a programmable electrothermal device for reproducibility. The discharge chamber was a commercially available vacuum chamber adapted for both flowing and static gas environments. Operational parameters, such as chamber pressure, discharge voltage, sample volume, and cathode cup diameter were evaluated for maximum fluorescence signal. The maximum signals were observed at discharge voltages of 480 V for solid samples and above 1000 V for aqueous samples. The chamber pressure (2–14 Torr) was not critical. Sample sizes of over 40 μl gave no signal increase. Maximum fluorescence signals were obtained 10–15 s (60 000–90 000 shots) following the initiation of laser-discharge pulsing. Linear calibration curves were obtained for lead and iridium with limits of detection of 15 fg and 2 pg, respectively. Although the signal was higher in a static gas environment, the signal to noise ratio was lower than in a flowing gas system.