No abstract

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.

A standardized procedure for collecting dust samples from surfaces using a micro-vacuum sampling technique was evaluated. Experiments were carried out to investigate the collection efficiency of the vacuum sampling method described in ASTM Standard D7144, "Standard Practice for Collection of Surface Dust by Micro-Vacuum Sampling for Subsequent Metals Determination." Weighed masses ( approximately 5, approximately 10 and approximately 25 mg) of three NIST Standard Reference Materials (SRMs) were spiked onto surfaces of various substrates. The SRMs used were: (1) Powdered Lead-Based Paint; (2) Urban Particulate Matter; and (3) Trace Elements in Indoor Dust. Twelve different substrate materials were chosen to be representative of surfaces commonly encountered in occupational and/or indoor settings: (1) wood, (2) tile, (3) linoleum, (4) vinyl, (5) industrial carpet, (6) plush carpet, (7,8) concrete block (painted and unpainted), (9) car seat material, (10) denim, (11) steel, and (12) glass. Samples of SRMs originally spiked onto these surfaces were collected using the standardized micro-vacuum sampling procedure. Gravimetric analysis of material collected within preweighed Accucapinserts (housed within the samplers) was used to measure SRM recoveries. Recoveries ranged from 21.6% (+/- 10.4%, 95% confidence limit [CL]) for SRM 1579 from industrial carpet to 59.2% (+/- 11.0%, 95% CL) for SRM 1579 from glass. For most SRM/substrate combinations, recoveries ranged from approximately 25% to approximately 50%; variabilities differed appreciably. In general, SRM recoveries were higher from smooth and hard surfaces and lower from rough and porous surfaces. Material captured within collection nozzles attached to the sampler inlets was also weighed. A significant fraction of SRM originally spiked onto substrate surfaces was captured within collection nozzles. Percentages of SRMs captured within collection nozzles ranged from approximately 13% (+/- 4 - +/- 5%, 95% CLs) for SRMs 1579 and 2583 from industrial carpet to approximately 45% (+/- 7 - +/- 26%, 95% CLs) for SRM 1648 from glass, tile and steel. For some substrates, loose material from the substrate itself (i.e., substrate particles and fibers) was sometimes collected along with the SRM, both within Accucaps as well as collection nozzles. Co-collection of substrate material can bias results and contribute to sampling variability. The results of this work have provided performance data on the standardized micro-vacuum sampling procedure.