A MICROMETHOD FOR THE DETERMINATION OF SULPHATE BY FLAME PHOTOMETRY
A micromethod for the determination of 0.1 to 3.5 μg of sulphate is described. Acidified barium chloride solution is added to samples containing free and esterified sulphate, and the resultant mixtures are dried at 95 °C. Soluble materials are redissolved with a 90% solution of acidified ethanol, 0.1 N for hydrochloric acid, containing 250 μg lithium per milliliter. After addition of the ethanol solution, approximately eight hours are required for the establishment of equilibrium (as indicated by a radiosulphur label) between solid and dissolved barium sulphate. Barium present in solution is then determined quantitatively by flame photometry, with the ethanol–lithium medium increasing the primary emission of the barium by 15 times. The sulphate content of the sample is read from a standard curve. Estimations on microgram quantities of some organic and inorganic sulphur-containing compounds are given.