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An Automated Total Protein Nitrogen Method

1975; Oxford University Press; Volume: 58; Issue: 6 Linguagem: Inglês

10.1093/jaoac/58.6.1221

0004-5756

Larry L Wall, Charles W. Gehrke,

Analytical chemistry methods development

Abstract A rapid automated method for total protein nitrogen has been developed, using the Technicon AutoAnalyzer with block digestor. Ammonia is determined by the automated ammoniasalicylate reaction at a rate of 40 samples/hr. A number of variations in digestion parameters have been evaluated. Hydrogen peroxide was used as a digestion accelerator. A salt-acid ratio of 1:1 and a block temperature of 425°C were chosen. The catalysts evaluated included HgO, CuS04, Se02, and Ti02/CuS04. Maximum nitrogen recovery in the shortest time (30 mill) was achieved with HgO as the catalyst. The results from multiple analyses of 10 experimental samples of different refractoriness with the block digestor method, using HgO or CuS04 as a catalyst, compared well with the results by the official AOAC Kjeldahl method. The accuracy, precision, economy, and saving of space offered by the Missouri-Technicon block digestor method make this an attractive alternative to classical Kjeldahl analysis for large numbers of total protein determinations in samples of different refractoriness. The AutoAnalyzer cartridge manifold is simple and reproducible in its performance, and a large dilution of the sample is made on dialysis which eliminates the matrix effects from the sample digests. At least 250 samples can be analyzed in 9 hr with 1 instrumentation setup.