In connection with EC Directives, it is necessary to develop methods for the measurement of hazardous substances in workplace air in accordance with the general performance requirements of EN 482. A class of compounds for which acceptable methods were not generally available are the more volatile and more polar organic vapours.
A standard method for the measurement of volatile organic compounds in workplace or environmental air involves the sampling of the polluted air onto a suitable sorbing agent, contained in a sampling tube, followed by recovery of the sample by thermal desorption. The usual method uses Tenax as sorbing agent, but this is not suitable for very volatile or very polar compounds because of its low capacity for these compounds.
The objective was to recommend, if possible, a single sorbent that would be appropriate for the measurement of a wide range of volatile organic compounds in air. The sorbent would be deemed to be appropriate if the performance of the standard method, using this sorbent, met the CEN performance criteria. If this were not possible, a small number of sorbents, possibly in a combination tube, would be recommended.
The sorbent which satisfied the above acceptance criteria for the largest number of compounds was Chromosorb 106. It is therefore recommended for use when sampling the more volatile and polar organic vapours encountered in workplace atmospheres. However, a number of other sorbents also satisfied the above acceptance criteria for the majority of compounds and are suitable for a more limited (higher molecular weight) range of organic vapours. These sorbents included CARBOTRAP, TENAX GR, TENAX TA and CARBOPACK B. Carboxen 569 is recommended for sampling extremely volatile compounds such as ethylene oxide, propane and methanol.
An initial feasibility study was undertaken by the Co-ordinator in order to prepare a short-list of sorbents from those available commercially. Using 19 test compounds, the five most promising sorbents were then evaluated on the basis of sorbent sampling capacity, analyte recovery, overall uncertainty in accordance with EN 482, recovery after storage and background levels of analyte. The five sorbents were examined by 12 participating laboratories, each laboratory being allocated a sorbent with which they were particularly familiar. Each sorbent was thus evaluated independently by at least two laboratories, enabling cross-checking of results. Carboxen 569 was also evaluated in a separate exercise for the three most volatile test compounds, as none of the short-listed sorbents had been satisfactory.