PERFORMANCE EVALUATION OF THE BABCOCK AND ETHER EXTRACTION METHODS - 1989 THROUGH 1992

Results of the collaborative studies of the performance of the Babcock method (989.04) and the modified Mojonnier ether extraction method (9 89.05) for the determination of the fat content of raw milk were publi shed in 1988. Method performances were characterized by using the harm onized International Organization for Standardization-International Un ion of Pure and Applied Chemistry-Association of Official Analytical C hemists (ISO/IUPAC/AOAC) guidelines for method validation, and the met hods were approved official first action. During 1989 through 1992, th e split-sample collaborative study format was used to monitor the perf ormance of these methods as a part of an ongoing quality assurance pro gram for a group of laboratories. Seven blind duplicate samples of raw milk were sent from a central laboratory once every 2 months to each participating laboratory (11 to 17 laboratories). Data were analyzed b y using the same statistical procedures used in the 1988 study. Over t ime, both the within- and between-laboratory performances of both meth ods were as good as or, in most cases, better than the results from 19 88. The data demonstrate that the statistical protocol for collaborati ve studies can be used effectively as the basis for a multilaboratory quality assurance program and that the method performance achieved in a collaborative study can be maintained and even improved with time.