ABSTRACT
Composite testing-like parts (combining like paints from several like parts or products to obtain sufficient sample size for analysis when there is insufficient quantity of paint on one item to perform testing) are appropriate and may be necessary to obtain valid analytical results. Composite testing-different parts (combining different paints, e.g., multiple colours from one or more samples to reduce the number tested) must be done with adequate care, planning and understanding of the limitations and propagations of error in measurements or the test may fail to detect excessive lead in one individual paint because of dilution. If composite testing-different parts are used, great care must be taken to accurately weigh each component paint and account for the propagation of errors due to weighing and measuring, and the analyst must ensure that the compositing will not result in a Pb measurement being below the detection limit for a paint component that would exceed 0.009% Pb. Each individual paint must be weighed individually with sufficient precision and sufficient safety factors to assure that no false negatives are reported. Sufficient paint must be used for each of the paints giving proper consideration for the weighing capabilities of the balance used and the detection limits and necessary dilution for the subsequent instrumental analysis. The combined paints could then be digested according to the procedure given below for a single paint before analysis by inductively coupled plasma (ICP) spectroscopy. Appropriate weights for each of the individual paints that are composited depend on final dilution volumes, weighing accuracy and detection limits. All of the lead found in the digestate for the combined composite could be attributed to the weight of each of the individual paints as though all of the lead could possibly come from any one of the individual paints. The measured lead should be treated in calculations as if it originated solely from one part of the composite; the lead concentration calculation should be carried out for each part unless identical weights of each sample were used in the analysis. It is imperative that a sufficient ‘safety factor’ be applied to account for weighing inaccuracy and propagation of errors from each step in
samples, that any sample possibly having greater than 80% of the limit for lead in paint in any of the composited paints should be retested (1, 2)
Example of composite testing – lead in surface coating material Method: CPSC test method: CPSC-CH-E1003-09.1 – Standard operating procedure for determining lead (Pb) in paint and other similar surface coatings.
