Reduction of nitrate prior to kjeldahl digestion

Abstract

Abstract A new method is described for reducing nitrate prior to Kjeldahl digestion of soil and crop samples. Zinc is used to reduce CrIII to CrII, which in turn reduces NO 3 —N. Zinc powder is mixed with the sample, a solution of CrK(SO 4 ) 2 in H 2 SO 4 added and the mixture allowed to stand at room temperature for 2h. The usual Kjeldahl reagents (K 2 SO 4 , CuSO 4 and H 2 SO 4 ) are then added and the digestion completed in a digestion block at 360°C. Nitrate is quantitatively converted to NH 4 —N, whether on its own, in plant material or in soil.