Nessler′s Reagent-Spectrophotometric Determination of Total Nitrogen in Soil

A method for the determination of total nitrogen in soil by Nessler′s reagent-spectrophotometry was proposed. The soil sample was digested with H2SO4 using CuSO4 as accelerator. Acidity of the sample solution was adjusted to ca. pH 10 by addition of 400 g·L-1 NaOH solution, and the solution together with precipitate was made up to 200 mL in a volumetric flask. An aliquot of 10 mL of the supernatant was taken and placed in a 50 mL colorimetric tube, sodium potassium tartrate solution was added as complexing agent and Nessler′s reagent added as coloring agent, and made up to 50 mL with water. Its absorbance was measured at the wavelength of 420 nm, and the content of total nitrogen was calculated. Linear relationship between values of absorbance and mass concentration of nitrogen was kept in the range within 2 mg·L-1. The proposed method was applied to the analysis of soil samples, giving results in consistency with those obtained by titrimetry with RSD (n=10) of 0.24%. Values of recovery were found in the range of 92.3%-112%.