INTERLABORATORY AND INTRALABORATORY VARIABILITIES IN THE ENVIRONMENTAL LEAD PROFICIENCY ANALYTICAL TESTING (ELPAT) PROGRAM

The Environmental Lead Proficiency Analytical Testing (ELPAT) Program evaluates over 400 laboratories that perform lead measurements in pain ts, soils, and dusts. A previous National Institute for Occupational S afety and Health study, based on the ELPAT data over a 3-year period ( 1992-1995), found no large biases among common hotplate and microwave digestion technique, but did detect small consistent bias between two common instrumental methods. This study expands on the earlier study b y examining the total sample variability and its variation components (interlaboratory and intralaboratory). A correlation model was used to separate the variation components by estimating a variation ratio. Th e correlation model leads to a more general approach than a sample pai ring technique developed by Youden. This study found no significant ev idence that the relative contribution of intralaboratory and interlabo ratory variability to total variability charges with lead loading leve ls. There were no significant differences in the relative contribution of variation components among three most commonly use analytical meth ods (combinations of sample preparation techniques and instrumental me thods). The interlaboratory relative standard deviation is about 1.7 t imes the intralaboratory relative standard deviation. Both variation c omponents are important parts of total variation although the laborato ry-to-laboratory (including analyst-to-analyst) difference is greater than the within laboratory (including sample-to-sample) variation.