Application of Quality Control Procedures to Environmental Radioassay-Iodine-131 in Milk

Abstract

In a widespread surveillance program of environmental radioactivity such as that carried out by the Division of Radiological Health, U.S. Public Health Service, reliability of analytical data is of primary importance if measurements by different laboratories are to be comparable and valid. This paper describes the application of quality control techniques to the analysis of samples of fluid milk. The specific technique used for examining the data was the control chart, which was applied to samples of known radionuclide content. This technique facilitated the study of the analytical data so that laboratories producing divergent data could be identified and corrective measures instituted. As practiced under this program, specially prepared samples of milk with known iodine-131 concentrations were analyzed by the laboratories in their routine manner, and the resulting analytical data were statistically compared with the expected values. Control charts were so constructed as to determine whether the accuracy, including precision and bias, of reported results met empirically selected criteria. Through periodic submission of samples, the control-chart method produced a record of laboratory response to quality control efforts. Data depicting the improvement of laboratory agreement with known values, for two sets of samples submitted several months apart, illustrate the usefulness of this quality control measure.