9.
Interlaboratory Comparison Studies for Characterization of Organic
Compounds in Particulate Matter
Michele
M. Schantz and Stephen A. Wise
NIST,
Analytical Chemistry Division, 100 Bureau Drive Stop 8392, Gaithersburg,
MD 20899-8392; Joellen Lewtas, USEPA, NERL, Manchester Lab, 7411
Beach Dr. E., Port Orchard, WA
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.
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