Determination of nitrogen in cheese using copper sulphate as a Kjeldahl catalyst: results of an inter-laboratory study

Abstract

An inter-laboratory study was carried out to establish precision parameters for a standard method used to determine nitrogen in cheese employing copper sulphate as a Kjeldahl catalyst. Blind duplicates of six cheeses were analysed by ten laboratories. Statistical analysis was carried out, identifying outliers and stragglers according to the Cochran and Dixon tests. Precision values of repeatability 0.12 and reproducibility 0.18 were evaluated from the results of eight laboratories and recommended for application in the analysis of cheeses that contain nitrogen in the range 2.5–4.0 g per 100 g of cheese.