INTER-LABORATORY STUDIES ON PRECISION CHARACTERISTICS OF ANALYTICAL METHODS .2. DETERMINATION OF NITRATE CONTENT IN MILK AND MILK-PRODUCTS - XYLENOL METHOD

As required by the German Food Law precision characteristics of the xylenol method to determine the content of nitrate in milk products have been established on the basis of inter-laboratory studies. The repeatability is for milk powder containing 12 mg nitrate/kg r = 3 mg/kg with S(r) = 1.06 mg/kg, for whey powder containing 106 mg nitrate/kg r = 9 mg/kg with S(r) = 3.18 mg/kg, for freeze dried cheese containing 92 mg nitrate/kg r = 7 mg/kg with S(r) = 2.47 mg/kg and for freeze dried cheese containing 8 mg nitrate/kg r = 2 mg/kg with S(r) = 0.71 mg/kg. The reproducibility is for milk powder containing 12 mg nitrate/kg R = 7 mg/kg with S(R) = 2.47 mg/kg, for whey powder containing 106 mg nitrate/kg R = 17 mg/kg with S(R) = 6.01 mg/kg, for freeze dried cheese containing 92 mg nitrate/kg R = 23 mg/kg with S(R) = 8.13 mg/kg and freeze dried cheese containing 8 mg nitrate/kg R = 4 mg/kg with S(R) = 1.41 mg/kg.