Diffusive sampling of C7-C16 hydrocarbons in workplace air: uptake rates, wall effects and use in oil mist...

The measurement of semi-volatile hydrocarbons in workplace air is complicated by their readiness to condense to form aerosols or adsorb on to surfaces. The diffusive sampling and analysis by thermal desorption of alkanes up to hexadecane was investigated with the aim of quantifying vapour from petroleum distillate fractions and possibly differentiating particles from vapour in oil mist measurements of light mineral oil-based metalworking fluids. Diffusive uptake rates were measured on Perkin Elmer thermal desorption tube samplers packed with Tenax TA, and the potential for deposition within the tubes was examined. Hydrocarbon vapour was found to adsorb on the oxide layer that can develop on the sampler's internal walls. General measurements of mixed hydrocarbon vapours (i.e. petroleum distillate fractions) should not be unduly affected if concentrations are greater than approximately 5 mg m(-3) and the tubes are in good condition. For the purposes of differentiating light mineral oil mist and vapour from a total hydrocarbon measurement, it is unlikely that measuring the vapour separately could be used to calculate mist concentrations <3 mg m(-3) with sufficient accuracy.