Emission characteristics and the limit of determination of alkali metal lines excited by a Grimm glow discharge plasma

In Grimm glow discharge optical emission spectrometry, the emission characteristics of the spectral lines of sodium and lithium were investigated. The atomic resonance lines, derived from the lowest excited levels, such as Na I 588.99 nm and Li I 670.78 nm, are very intense, and are thus available for trace determinations. However, such resonance lines suffered from severe self-absorption, especially in samples containing larger amounts of sodium or lithium, which led to nonlinear relations between the observed emission intensity and the concentration. It is thus an effective solution to use self-absorption free lines, such as Na I 330.23 nm and Li I 323.26 nm, instead of the resonance lines. The limit of determination, which was defined as the sample concentration corresponding to ten-times the average fluctuation of the backgrounds, was estimated to be 3 × 10-3 at.% for Na I 588.99 nm and 4 × 10-3 at.% for Li I 670.78 nm.