The performance of laboratories analysing heavy metals in the Workplace Analysis Scheme for Proficiency (WASP)

This paper discusses the proficiency of laboratories analysing identical test samples representative of metals in air in the Workplace Analysis Scheme for Proficiency (WASP) and the variability of results from laboratories used to assess personal exposure in the workplace. Over 11 years, the performance of laboratories has significantly improved for lead, cadmium and chromium. Laboratories show better agreement when using inductively coupled plasma-atomic emission spectroscopy (ICP-AES) than flame atomic absorption spectroscopy (FAAS) when analysing chromium, but not when analysing lead and cadmium. Data from the proficiency testing scheme show that for a customer to have confidence that a measurement value does not exceed the workplace exposure limit the analytical result would have to be <134 microg m(-3) for lead and 23 microg m(-3) for cadmium for an 8 h sample and 129 microg m(-3) for lead, 21 microg m(-3) for cadmium and 429 microg m(-3) for chromium for a 4 h sample (for samples with relatively soluble matrices), before considering the further uncertainties due to sampling. The performance criterion for satisfactory performance (+/-8.3%) was found to be appropriate as long as laboratories participated consecutively in all rounds. Estimates of the overall uncertainty of results from ICP-AES and FAAS analysis were shown to meet the criteria in EN482. Samples from some types of workplace environments are more difficult than the WASP test material to dissolve into solution, so it is expected that estimates of uncertainty are larger for less soluble analytes and matrices. WASP has now initiated a programme to help laboratories assess their performance with more complex matrices.