A Guide to Using SRM 2569 to Validate Analytical Methods
John R. Sieber, John L. Molloy
A users guide is presented for Standard Reference Material (SRM) 2569 Lead in Paint Films for Childrens Products. This SRM consists of paint films on coupons of polyester with the paint characterized for mass fraction of Pb, mass of Pb per unit area, paint coating thickness, and paint coating density. This guide was written to instruct users who must critically evaluate a non-destructive test method, typically based on X ray fluorescence spectrometry (XRF). Users of SRM 2569 are known to have a wide range of analytical expertise. In addition, many users have purchased their XRF method as a package consisting of an instrument and prepackaged methodology, suggesting that many users have little or no experience with XRF or with validation of test methods using reference materials. This guide provides some suggestions of logical approaches to the use of SRM 2569 and discusses aspects of method validation, including documentation of repeatability and testing for bias. For example, the SRM is not recommended for use as a routine control chart material because frequent handling will cause the coupons to deteriorate rapidly. The homogeneity of SRM 2569 is well characterized, and it is known that the composition of Level 2 results in a greater difficulty of data interpretation as analysis area decreases. Methods of addressing this issue are discussed, centering on measurement of at least three independent locations on an SRM coupon and calculating the median of the replicate Pb results for use in comparisons.