Evaluation of a U-shaped direct current plasma arc for the determination of lithium in aluminium alloys by atomic emission and atomic absorption spectrometry

Abstract

The applicability of a U-shaped d.c. arc with sample introduction in the form of an aerosol for the determination of lithium has been demonstrated. The plasma produced was used as the excitation source for atomic emission spectrometry and as the absorption cell for atomic absorption spectrometry (AAS). The fairly good cylindrical symmetry of the horizontal analytically useful portion of the arc allows emission and absorption observations in directions parallel to the arc axis. Maximum signals were observed in zones 3.9 and 7.5 mm from the arc axis for emission and absorption, respectively. For the emission measurements, the limit of detection was 0.003µg l^–1 and the linear dynamic range covered five orders of magnitude. For the atomic absorption measurements, a characteristic concentration (1% absorption) of 50 µg l^–1 and a limit of detection of 4 µg l^–1 were obtained, while the shape of the calibration graph resembled that obtained for conventional flame AAS. Interferences from aluminium on the emission and absorption signals were investigated. An analytical procedure for the determination of lithium in aluminium alloys was established and tested on several samples.