COMPARISON OF MERCURY AND COPPER-BASED CATALYSTS IN THE KJELDAHL DETERMINATION OF NITROGEN IN MEAT AND MEAT-PRODUCTS - COLLABORATIVE STUDY

A copper catalyst for use in AOAC Method 928.08, Nitrogen in Meat, Kje ldahl Method, was subjected to a collaborative study in which it was c ompared 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 h am). On the average, protein concentrations obtained with the copper c atalyst were lower than those obtained with the mercury catalyst by ap proximately 1% of the protein content of the meat. For example, with a sample containing 15% protein, the results obtained with mercury woul d be expected to be 0.15% higher than those obtained with copper. This difference is within the reproducibility standard deviations of the m ethods. The repeatability standard deviation with copper was on the av erage approximately 17% larger than that obtained with mercury, but th e reproducibility standard deviations for the 2 procedures were not, s tatistically, significantly different. The Kjeldahl method for nitroge n determination in meat and meat products using copper catalyst has be en adopted first action by AOAC INTERNATIONAL.