Theoretical considerations on the indirect determination of anions : Determination of sulphate with barium chloranilate

Abstract

Some anions (sulphate) may be determined by their reaction with a slightly dissociated or slightly soluble compound (barium chloranilate), another anion (chloranilate ion) being liberated and its extinction measured. An equation is given in this paper for the relationship between the concentration of sulphate and the extinction. For low concentrations the equation is non-linear. A calibration curve, prepared under standardised conditions, agrees well with theory. It shows a precision of about 5 % at 20 μg of sulphate. At higher levels the precision is slightly better. It is proved that many interferences of foreign ions may be explained quantitatively by consideration of the activity coefficients. The scope of this method is discussed.