Development of an international standard for the determination of metals and metalloids in workplace air using ICP-AES: evaluation of sample dissolution procedures through an interlaboratory trial

Inductively coupled plasma atomic emission spectrometry (ICP-AES) is rapidly overtaking atomic absorption spectrometry (AAS) as the method of choice for the determination of toxic metals in workplace air. However, the few ICP-AES methods that have been published are not well characterised in terms of the effectiveness of the sample dissolution procedures described and their validation status. The International Standards Organization (ISO) is currently engaged in developing ISO 15202, which will describe a generic method for the determination of metals and metalloids in airborne particulate matter by ICP-AES. One part of the proposed standard deals with dissolution procedures. The ISO work has been supported by a project carried out in the authors' laboratory to identify, develop and validate sample dissolution procedures for inclusion in the proposed standard. This paper describes an interlaboratory comparison carried out to assess the performance of selected procedures using samples of airborne particulate matter collected on filters with a multiport sampler. Five dissolution procedures were tested. These included an ultrasonic agitation procedure, two hot-plate procedures (based upon NIOSH 7300 and OSHA ID 125G) and two microwave-assisted procedures (based upon EPA 3052). It was shown that the dissolution procedures selected for use in the trial and used internally at HSL generally gave equivalent performance. As expected, a wider spread of results was obtained by participants in the trial. More specifically, there exists some reservation regarding the ability of the ultrasonic and hot-plate procedures to attack fully on a consistent basis some resistant materials, e.g., chromium containing particulate matter. Above all, the trial demonstrated the usefulness of microwave-assisted dissolution procedures in a modern laboratory.