9. Interlaboratory Comparison Studies for Characterization of Organic Compounds in Particulate Matter

A working group of investigators, who are characterizing and quantifying the organic compounds in particulate matter (PM) as part of the US EPA’s PM 2.5 research program and related studies, was established five years ago to advance the quality and comparability of data on the organic composition of PM. This group has completed two interlaboratory comparison studies. The first study used a subset of SRM 1649a (Urban Dust, sieved to <123 mm) that had been sieved to <63 mm (Air Particulate I) as an unknown PM sample. In addition to Air Particulate I, the participants received a dichloromethane extract of Air Particulate I as a second unknown sample and a sample of SRM 1649a for use as a control material. For the second study, initiated in March 2002, the participants received a sample of PM2.5 collected recently in Baltimore, MD along with a sample of SRM 1649a. It is a requirement that all participants return data on Air Particulate I and SRM 1649a prior to receiving the Baltimore PM2.5 material. To date 25 laboratories have received samples for the first study and 16 laboratories have received samples for the second study. The target analytes include polycyclic aromatic hydrocarbons (PAHs), nitrated PAHs, alkanes (including hopanes and cholestanes), sterols, carbonyl compounds (ketones and aldehydes), acids (alkanoic and resin), phenols, and sugars. Because this is a performance-based study, laboratories are encouraged to use the methods that they are routinely using in their laboratories to analyze similar samples. Laboratories are requested to return data from three analyses (subsamples) of each sample provided along with a summary of the methods used. The data received from the participating laboratories, following outlier testing, are then used to assign a consensus value to each analyte in the unknown samples. Results are used in the consensus value assignment for the unknown PM sample only if the laboratory’s results for SRM 1649a are within 30% of the uncertainty limits of the certified values. The consensus values, accuracy and precision assessments, and the methods used by each laboratory are summarized in a report provided to the participants. In this report, laboratories are numerically identified with only the laboratory and the exercise coordinators knowing this numerical identification. A meeting of the participants is also held to discuss the results and the methods used by the laboratories. The results from the two interlaboratory exercises will be presented along with plans for future exercises. This work has been funded by the U S Environmental Protection Agency. It has been subjected to Agency review and approved for publication.