CCQM-K50: Polycyclic aromatic hydrocarbons (PAHs) in soil/particulate matter

There are numerous Calibration and Measurement Capability Claims (CMCs) on PAH analysis in various matrices published in the BIPM key comparison database, Appendix C. By July 2007 such CMCs were released in Category 10 Biological fluids and materials, Subcategory 10.4 Tissues, Category 11 Food, Subcategory 11.2 Contaminants and Category 13 Sediments, soils, ores and particulates, Subcategories 13.1 Sediments, 13.2 Soils and 13.4 Particulates. CCQM comparisons are needed to underpin these claims. A pilot study CCQM-P69 'PAHs in soil' was successfully conducted in 2004. After review of the results at the OAWG meeting in September 2005 it was decided to proceed with a key comparison and a concurrent second pilot study CCQM-K50/P69.1. CENAM and BAM agreed to coordinate the intercomparison. The measurand of the study was specified as amount of specific PAHs in solid matrices as extracted under exhaustive extraction conditions. As for the preceding pilot study and two studies for PAHs in solution (CCQM-P31a and CCQM-K38), five target analytes, phenanthrene, fluoranthene, benz[a]anthracene, benzo[a]pyrene and benzo[ghi]perylene, were selected as representative of the measurement of individual compounds. The CCQM-K50 study utilized a soil sample from BAM and an air particulate sample from NIST. Both materials were naturally contaminated, not enriched or spiked. The mass fraction of target analytes in the samples ranged from 2 mg/kg to 15 mg/kg. NIST SRM 1649a Urban Dust was provided as a control material. Participants were requested to determine the mass fraction of the selected PAHs on a dry mass basis and submit a complete uncertainty budget for their measurements. Ten NMIs participated in the study. All participants applied Soxhlet or Accelerated Solvent extraction (ASE) and GC-MS with either deuterated or 13C labelled internal standards. Results demonstrate a good level of equivalence in capabilities of the participating NMIs to identify and measure PAHs in highly contaminated environmental samples. With a few exceptions, data agree within the range plus or minus 5% from the Key Comparison Reference Value (KCRV) for the soil and plus or minus 10% from the KCRV for the particulate. Relative expanded uncertainties of the KCRV range from 2% to 5% for the soil and from 4% to 13% for the particulate matter. The KCRV was agreed upon during the OAWG meeting in November 2008 as the arithmetic mean of participants' results. Data of laboratories who did not take part in