Influence of catalyst,sample weight,and digestion conditions on Kjeldahl nitrogen

Abstract

The influence of catalyst (containing K₂SO₄/Cu/Ti, K₂SO₄/Se or Se alone), sample weight (0.2 or 0.4 g), and digestion blocks (Tecator DS 1015–20 or Tecator DS 1016‐ 40) on the Kjeldahl‐nitrogen (N) determination in pecan, corn, and turnip leaves was evaluated. Mean Kjeldahl‐N values were 1.84, 2.43, and 3.72 % for the pecan, corn, and turnip samples, respectively, which were significantly higher ( = 0.05) using K₂SO₄/Se as a catalyst, a 0.4 g aliquot of the sample, and a DS 1015–20 digestion block. The magnitude of the differences due to catalyst, sample weight, or digestion conditions did not affect the N diagnosis status when applying interpretative data for the selected crops. The higher standard deviation (SD) for the turnip leaves compared to the pecan or corn leaves may be due to a higher nitrate (NO₃) level in the turnip leaves. Selected catalyst, sample weight, and digestion conditions did not affect the SD, and therefore any combination of these factors could be used to determine Kjeldahl N. A protocol using K₂SO₄/Cu/Ti, a 0.4 g sample‐aliquot, and a digestion block equipped with condensers as the fume control system tended to give the lowest variance, and to be the most accurate and practical method.