INTERLABORATORY VALIDATION ANALYSIS OF TH E MINERALIZATION BY MICROWAVE DIGESTION - APPLICATION TO KJELDAHL NITROGEN IN FOODS

Microwave digestion is now considered as a useful technique that prese nts many advantages, such as speed and reagent economy, leading to low er cost and reduced pollution. It has been applied Successfully to foo d digestion and the purpose of this work is to determine the precision of this new digestion method. Microwave digestion of food samples for nitrogen determination was investigated in a collaborative study invo lving 11 laboratories. Digestions were performed with sulphuric acid, hydrogen peroxide, and no catalyst, in less than half an hour. The rin g test was accomplished on six different samples: milk, wheat four, po wdered egg, casein, meat and dactyl hay, all containing from 0.4 to 14 g/100 g of nitrogen. Relative standard deviations of repeatability an d reproducibility range from 0.12 to 1.76% and 1.26 to 2.64%, respecti vely. These results agree with the general performance accepted for th e reference method. Statistical evaluation indicated no significant di fference between the studied and the reference methods. Consequently, the new method has been officially designated as an alternative method for Kjeldahl determination by the French Association of Standardisati on (AFNOR).