assessed their performance against the above limits, and
decided whether repeats were necessary. All three laboratories
used the rapid Dumas method for nitrogen determination. This
measures the non-protein nitrogen as well as the protein
nitrogen, and hence gives higher results than the Kjeldahl
method.9 The difference is small, and Dumas is higher by a
factor of 1.014, which is more important for fish than for meat.
Therefore it is usual to quote the nitrogen result for both
methods of analysis as Kjeldahl is still widely used in laboratories
worldwide.