Kjel-Foss automatic analysis using an antimony-based catalyst: collaborative study

Collaborators in 7 Kjel-Foss laboratories and 1 manual Kjeldahl laboratory performed protein determinations on fishmeal: 10 with traditional mercury catalyst and 10 with a new antimony-based catalyst. Repeatability, interlaboratory variation, and variation vs. manual Kjeldahl were equal to or better with the new catalyst than with the mercury catalyst. In addition, 48 different products were analyzed: 5-10 determinations were made on each product with the mercury catalyst and 5-10 were made with the new catalyst. After the Kjel-Foss procedure was modified slightly with higher acid settings, the differences in recovery and repeatability of the 2 procedures were not more than +/- 1%.