The Measurement of AIr Pollutants by Gas Chromatography

The auto exhaust have been noticed as one of the main sources of organic pollutants in city air. The accurate method of analysis for pollutants in the atmosphere have not been established owing to their very low concentrations.The gas chromatographic technique have been applied in the study of air pollution, but, for the practical use, the cold trap technique is necessary to concentrate the sample before applying a gas chromatographic analysis.In this paper, to obtain the improved trapping column for gas chromatographic analysis of the low concentration organic pollutants in the city air, the effects of the different sizes and filling materials of trapping column and grain sizes of supporting material on the collecting efficiencies and the collecting methods were investigated by using Kotaki gas chromatography GD-2 (Tokyo, Japan). The experimental flow sheet is shown in Fig. 1. As the separating column the coiled copper tube (4 mm ID 10 m long) filled with 40% (wt) dimethyl sulfolanecrushed fire brick C-22 (20-30 mesh) was applied, and it was maintained at ice water temperature. During the charging of the sample the trapping column was cooled by liquid nitrogen. Hydrogen or helium was used as the carrier gas and its flow rate was regulated at 100 ml/min. The collecting efficiencies for the different traps were evaluated by the magnitude of the peak area and peak height on gas chromatogram.The results obtained were as follows.1) In applying the reducing pressure method for sample charging, the inside pressure of container should be at least reduced to 160 mmHg.2) The most effective collecting efficiency was obtained in the case of 20-30 mesh grain size of supporting material.3) It was ascertained that the most suitable trap size for practical application was 30 cm long and 4 mm I.D.4) It was desirable to use the trap filled with glass-wool (2 g) whose size was 20 cm long and 8 mm ID, in applying the direct aspirating method instead of the reducing pressure method.The relation between the collecting efficiencies and lengths of glass-wool trap is shown in Fig. 4