Determination of Air Pollutants: Application of a Low-Cost Method for Preparation of VOC Mixtures at Known Concentration

Abstract

Gas chromatography (GC) is an excellent tool to obtain qualitative and quantitative information on volatile organic compounds (VOCs) present in gaseous samples. However, to carry out an appropriate quantitative analysis of unknown samples, the use of known concentration gas mixtures, to exploit as standards, is required. Commonly, these mixtures are obtained from cylinders of compressed gas at known concentrations: this involves a considerable economic outlay and problems relating to their handling. This paper aims to apply a method, proposed as a versatile, simple, and economical alternative to the use of such cylinders, for preparing gaseous calibration standards useful to obtain calibration curves for quantification of air pollutants. In addition, the operative limits of this method were investigated. The method involves the continuous injection of volatile compounds in liquid form into a stream of neutral gas, such as air or nitrogen. Exploiting the high volatility of the compounds used, it is possible to generate a continuous gas stream containing the chosen VOC at the desired concentration based on the mass balance of the system. This method proved to be suitable for compounds with volatility ranging from 36 kPa to 0.1 kPa at 293 K and it showed relative bias and relative standard deviation (RSD) values of less than 16% and 8%, respectively. The described dynamic method results are repeatable and accurate. It can be used effectively for compounds with vapour pressure values within the stated limits and provides a more versatile and cost-effective alternative to compressed gas cylinders.