Determination of sulfur by molecular absorption of carbon monosulfide using a high-resolution continuum source absorption spectrometer and an air-acetylene flame

A standard air-acetylene flame, attached to a high-resolution continuum source atomic absorption spectrometer, was used to determine sulfur via measurements of selected rotational lines of carbon monosulfide (CS) formed in the flame. The lines are part of the strong molecular absorption system around 258 nm. Their half-widths in the order of a few picometers are comparable to common atomic lines. The analytical method is characterized by simplicity, rapidity, reliability, and robustness. Potential chemical and spectral interferences were tested using nitric, hydrochloric, perchloric and hydrofluoric acids at concentrations up to 5% (v/v), and solutions of Al, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, and Pb at concentrations up to 2000 mg L−1. The only serious spectral interference occurred with Pb at concentrations higher than 200 mg L−1, which is due to the formation of lead sulfate in the solution. The limit of detection achieved for sulfur was 2.4 mg L−1, using the CS line at 258.056 nm and a measurement time of 5 s. A linear dynamic range of more than 3 orders of magnitude was obtained. The analytical results were verified by means of standard reference materials, yielding good precision and accuracy.