Application of inductively-coupled plasma atomic emission spectrometry with an internal reference to the determination of sulfate and calcium in waters and brines

A method is described for the determination of sulfate and calcium in waters and brines; an inductively-coupled plasma is used with a multichannel vacuum spectrometer. Study of the behavior of the line-to-background intensity ratios for the S I 180.734, Ca II 317.933, Sc I 402.04 and Sc II 361.384-nm lines as functions of the observation height, aerosol carrier gas, power, and concentration of an easily ionized element shows that Sc II 361.384 nm can be used as an internal reference for sulfur and calcium. In the presence of high salt concentrations, the efficiency and quality of nebulization are degraded and at high aerosol gas flows in the presence of sodium, the line-to-background ratios for the ion lines are depressed and those of the atom lines are enhanced. However, under compromise conditions, the S I 180.734-nm and Ca II 317.933-nm lines exhibit significant freedom from interference caused by an easily ionized element. With the Sc II 361.384-nm line used as the internal reference, short-term precision is improved by a factor of 1.5–4, and long-term precision is improved by a factor of 2, producing data for sulfate and calcium that compare favorably with those obtained by gravimetry, titrimetry, and atomic absorption spectrometry. A detection limit of 70 μg l^?1 and a linear dynamic range of 1 g l^?1 were obtained for sulfate.