Purity evaluation of volatile organic compounds by GC-FID for standard gases and solutions using environmental analysis

Abstract

As the establishment of environmental quality standards is being promoted, the reliability of environmental analysis is one of the most important issues. The environmental problems caused by toxic organic substances in particular have become serious in recent years; therefore, there is much demand for standard gases and solutions for these analyses. Because the exact concentrations of these calibration standards are of great significance to obtain reliable measurement values, the concentrations and uncertainties of these calibration standards are required. Volatile organic compounds (VOCs), such as trichloroethylene and benzene, are part of the emission and environmental quality standards; therefore, the calibration standards of these VOCs are demanded for environmental analysis. To ensure the reliability of these calibration standards, purity evaluations of these VOCs are essential. In many cases the purity of VOC is evaluated by the relative peak area percentage of the main component only by GC-FID analysis for convenience and versatility. However, because of the various kinds of organic compounds, including stabilizers, in the VOC, the sensitivities of the compounds against the main component will be different by GC-FID. Although the identification and measurement of these impurities will offer valuable information for calibration standards and for preparing multi-component standard gases and solutions, these impurities are rarely analyzed. For these reasons, purity evaluations and information on impurities in VOCs have great meaning for preparing standard gases and solutions. The purpose of this study is to establish a purity evaluation method for VOCs by GC-FID to prepare accurate standard gases and solutions. We selected seventeen frequently used VOCs, and attempted to determine each impurity and to estimate their uncertainties. In our work, the internal standard is added directly to the target VOC for a quantitative analysis, rather than using another solvent for dilution. The relative sensitivities of the impurities against the internal standard are measured in advance. As a result, we can analyze trace impurities in VOC precisely, and calculate the purity and uncertainty by the subtraction method. The VOC calibration standards for environmental analysis can be easily provided by the method proposed in this study.