Determination of atmospheric benzene concentration by displacement following adsorption on silica gel.

In industries which employ solvents containing benzene, determination of the atmospheric content of this substance is an important and constant health problem. Many of the methods of assessing benzene concentration described in the literature, including those of Jacobs (1949) and Elkins (1950), entail determination of the total aromatic content, and estimation of the atmospheric benzene concentration according to these methods frequently requires more or less time-consuming laboratory work. Some methods, such as absorption in alcohol or other solvents, necessitate effective chilling of certain parts of the apparatus during sampling in order to minimize loss of benzene. This may be difficult in field work. Tiselius (1943) introduced a technique which may be used for various analytical purposes. The principle is that the fluid mixture to be analysed is adsorbed on, for instance, a column. of silica gel, and then displaced by a substance which is more strongly adsorbed than any of the components of the mixture. I have tested the displacement technique in analyses of atmospheric benzene concentration. Benzene vapour was adsorbed on silica gel. The eluent was absolute alcohol. The content of benzene in the percolate was determined. The advantages of the method are ease of sampling and concentration of the atmospheric benzene in a small quantity (1 to 5 ml.) of alcohol, which permits greater precision in the final spectrophotometric determination. Further, it is possible by means of absorption spectra to identify benzene in the ultra-violet region.