Ultrasonic extraction and portable anodic stripping voltammetric measurement of lead in paint, dust wipes, soil, and air: an interlaboratory evaluation.

Recent studies have demonstrated the utility of ultrasonic extraction (UE), followed by portable anodic stripping voltammetry (ASV), for the on-site determination of lead in environmental and industrial hygiene samples. The aim of this work was to conduct an interlaboratory evaluation of the UE-ASV procedure, with a goal of establishing estimates of method performance based on results from collaborative interlaboratory analysis. In this investigation, performance evaluation materials (PEMs) with characterized lead concentrations were used for interlaboratory testing of the UE-ASV procedure. The UE-ASV protocol examined has been promulgated in the form of two separate national voluntary consensus standards (one for UE and another for electroanalysis, which includes ASV). The PEMs consisted of characterized and homogenized paints, soils, and dusts (the last of which were spiked onto wipes meeting national voluntary consensus standard specifications), and air filter samples (mixed cellulose ester membrane) generated using characterized paints within an aerosol chamber. The lead concentrations within the PEMs were chosen so as to bracket pertinent action levels for lead in the various sample matrices. The interlaboratory evaluation was conducted so as to comply with an applicable national voluntary consensus standard that can be used to estimate the interlaboratory precision of a given analytical test method. Based on the analytical results reported by the participating laboratories, relative standard deviations (RSDs) for repeatability and reproducibility were computed for three different lead contents of the four PEMs. RSDs for repeatability were 0.019-0.100 for paints; 0.030-0.151 for soils; 0.085-0.134 for dust wipes; and 0.095-0.137 for air filters. RSDs for reproducibility were 0.127-0.213 for paints; 0.062-0.162 for soils; 0.085-0.134 for dust wipes; and 0.114-0.220 for air filters. With the exception of one of the air filter samples and one of the paint samples, the precision estimates were within the +/- 20% precision requirement specified in the US Environmental Protection Agency National Lead Laboratory Accreditation Program (NLLAP). The results of this investigation illustrate that the UE-ASV procedure is an effective method for the quantitative measurement of lead in the matrices evaluated in this study.

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 paints, soils, and dusts. A previous National Institute for Occupational Safety 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 techniques, but did detect small consistent bias between two common instrumental methods. This study expands on the earlier study by 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. The correlation model leads to a more general approach than a sample pairing technique developed by Youden. This study found no significant evidence that the relative contribution of intralaboratory and interlaboratory variability to total variability changes with lead loading levels. There were no significant differences in the relative contribution of variation components among three most commonly used analytical methods (combinations of sample preparation techniques and instrumental methods). The interlaboratory relative standard deviation is about 1.7 times the intralaboratory relative standard deviation. Both variation components are important parts of total variation although the laboratory-to-laboratory (including analyst-to-analyst) difference is greater than the within laboratory (including sample-to-sample) variation.