Comparative study of the determination of nitrates in calcareous soils by the ion-selective electrode, chromotropic acid and phenoldisulphonic acid methods

Abstract

A comparative study of the determination of nitrates in calcareous soils by the chromotropic acid, phenoldisulphonic acid and nitrate ion-selective electrode methods was investigated, using 0.02 N copper(II) sulphate solution as extractant, which, in addition to being a preservative for nitrates, helps filtration and eleminates interference by hydrogen carbonates in the ion-selective electrode method. Silver sulphate, which had no effect on either procedure, can be added to the extractant for the precipitation of chlorides.

Nitrate in soil suspensions was determined by the ion-selective electrode method. Nitrites if present were eliminated by acidifying the extract with 1 N sulphuric acid containing sulphamic acid.

To avoid reaction between soluble organic matter and sulphuric acid in the chromotropic acid method, reagents were added in two steps with continuous cooling. Nitrites were eliminated as in the ion-selective electrode method.

Both methods were faster than the phenoldisulphonic acid method and gave identical results; the correlation coefficient was 0.999 8.