The determination of microgram amounts of sulphate by emission spectroscopy of barium with a nitrous oxide-acetylene flame

Abstract

The sulphate content of aqueous solutions has been determined indirectly, in the ranges 0·5 to 5·0 and 1·0 to 10·0 p.p.m., from barium emission measurements. By using a slight excess of barium, the sulphate is precipitated in a 50 per cent. solution of propan-2-ol and its concentration is calculated from the decrease in the barium content of the solution. The amount of barium in solution is determined from its emission at 553·55 nm in a nitrous oxide-acetylene flame. The only major flame interference detected is that from the band emission of calcium; 410 p.p.m. of calcium gave an emission intensity equal to that of 1 p.p.m. of barium. Sulphate has been determined in both pure solutions and in synthetic sample solutions containing other electrolytes. Major interferences were noted for potassium and ammonium oxalate, sodium orthovanadate, nickel chloride and to a lesser extent for sodium fluoride and perchloric acid. The sulphur content of biological material, digested by oxygen-flask combustion, has been determined satisfactorily by using this method.