Indicator-tube method for the determination of benzene in air

Abstract

A linear colorimetric method for determining benzene vapours in air is described. The method is based on a colour reaction between the benzene vapours and 0·200-mm silica gel treated with 0·7 g ml^–1 of a 5 per cent. solution of cerium sulphate in fuming sulphuric acid. The glass tubes are filled with indicator powder to a length of 50 mm. The indicator tubes are calibrated experimentally for benzene concentrations of from 0 to 0·3 mg l^–1 when 500 ml of air are aspirated, and from 0 to 2·0 mg l^–1 when 100 ml of air are aspirated. The accuracy of the method is from ±15 per cent. for low concentrations of benzene and ±5 per cent. for high concentrations of benzene. The sensitivity is 0·005 mg l^–1. The method is not applicable in the presence of toluene and xylene.