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An Improvement in the Direct Nesslerization Method for the Determination of Total Nitrogen in Stored Sterile Milk

Department of Food Technology, University of Illinois, Urbana

ABSTRACT

Recently, Murthy and Herreid (4) in their studies on stored milk indicated that the direct Nesslerization method of Hetrick and Whitney (2), though useful in the case of fresh milk, can not be used for the study of nitrogen distribution in stored sterilized milk, because of the variable digestibility of the stored samples. To find a suitable method for the determination of micro-Kjeldahl nitrogen comparable to the macro-method, the following direct Nesslerization method based on those of Lang (3) and Hetrick and Whitney (2) was investigated and found satisfactory.

MICRO-ANALYTICAL PROCEDURE

Reagents

1. Digestion mixture: 40 g. of K²S0⁴ (C.P.) and 2 ml. of SeOCl² (technical grade) are made up to 250 ml. with ammonia-free water and this solution is mixed with 250 ml. of H²SO⁴ (C.P.)
   
2. Nessler's Reagent: 50 g. of KI (C.P.) is dissolved in 35 ml. of cold ammonia-free water and a saturated solution of HgCl² (C.P.) is added until the orange precipitate formed persists.