SYSTEMATIC-ERRORS WITH THE USE OF INTERNAL STANDARD CALIBRATION IN GAS-CHROMATOGRAPHIC HEADSPACE ANALYSIS

The specificity of the use of internal standard calibration in headspace analysis was studied. An equation was derived that differed from the conventional equation by a factor (Vg + KgVl)/(Vg + KiVl), where Vg and Vl are the volumes of the gaseous and the liquid phases, respectively, and Ki and Ks are the distribution constants between the phases of the analyte i and the internal standard s, respectively. This factor is generally not equal to unity. Its magnitude, and hence that of the systematic error, is demonstrated by using literature values and experimental data obtained by analyses of model blood and water samples. It is shown that the use of the internal standard technique does not generally eliminated the matrix effect which is a serious problem in quantitatives headspace analysis. © 1990.