Evaluation of the continuous optical discharge for spectrochemical analysis

Abstract

The continuous optical discharge (COD) has been studied as a spectrochemical excitation source for atomic emission spectroscopy. The COD was generated by focusing a 45-W cw-CO 2 laser beam in Xe gas at pressures between 1150 and 3200 torr. The high temperature ( 10 000 K) and electron density (~10 17 cm −3) of the plasma should provide good excitation for elements difficult to excite by more conventional sources. Some characteristics of the plasma were examined as a function of laser power and gas pressure. The design of a gas cell for analytical measurements which increases plasma stability is presented. Linear calibration curves for O 2; and Cl 2 introduced into the plasma were obtained and detection limits established. Detection limits were also determined for solid materials laser ablated into the COD. Because the COD operates at pressures above atmospheric, gas samples are most easily introduced for analysis. To prevent contamination of optical components by analyte dissociation products, the COD should be operated as a plasmatron.