Comparison of Mercury and Copper Based Catalysts in the Kjeldahl Determination of Nitrogen in Meat and Meat Products: Collaborative Study

Abstract

A copper catalyst for use in AOAC Method 928.08, Nitrogen in Meat, Kjeldahl Method, was subjected to a collaborative study in which it was compared to the standard mercury catalyst. Nine laboratories (including one author’s laboratory) performed blind duplicate determinations of the protein content of 4 samples from each of 6 products (ground beef, canned ham, smoked ham, pork sausage, cooked sausage, and dry cured ham). On the average, protein concentrations obtained with the copper catalyst were lower than those obtained with the mercury catalyst by approximately 1% of the protein content of the meat. For example, with a sample containing 15% protein, the results obtained with mercury would be expected to be 0.15% higher than those obtained with copper. This difference is within the reproducibility standard deviations of the methods. The repeatability standard deviation with copper was on the average approximately 17% larger than that obtained with mercury, but the reproducibility standard deviations for the 2 procedures were not, statistically, significantly different. The Kjeldahl method for nitrogen determination in meat and meat products using copper catalyst has been adopted first action by AOAC INTERNATIONAL.