Measurement of Henry's Law Constants Using Internal Standards. A Quantitative GC Experiment for the Instrumental Analysis or Environmental Chemistry Laboratory

Abstract

An internal standard method applicable to undergraduate instrumental analysis or environmental chemistry laboratory has been designed and tested to determine the Henry's law constants for a series of alkyl nitriles. In this method, a mixture of the analytes and an internal standard is prepared and used to make a standard solution (organic solvent) as well as a dilute aqueous solution. Both the standard solution and the headspace samples above the aqueous solution at partitioning equilibrium in closed containers are subject to gas chromatographic (GC) analysis. The dimensionless Henry's law constants, Hi, of the analytes can be calculated from the known Hi of the internal standard and the GC peak area ratios. The temperature dependence of Hi may also be studied through the collaboration among several student groups. The experiment is methodologically simple and can be completed in less than four hours. However, the approach is only applicable to compounds that have dimensionless Henry's law constants in the order of 10–3 or less.