HEADSPACE-GAS CHROMATOGRAPHY - THE INFLUENCE OF SAMPLE VOLUME ON ANALYTICAL RESULTS

The role of the volume of the sample and the sample vial in equilibrium headspace-gas chromatography is discussed. A new term, the sample phase fraction (PHI-S) is introduced. It is shown that if the value of PHI-S is kept constant, the vial's volume has no influence on the "sensitivity" of the headspace analysis (which is proportional to the concentration of the analyte in the headspace). In a given headspace sampling system, concentration of the compound of interest in the headspace (c(G)*) at equilibrium is related to the value of PHI-S: a higher PHI-S will increase c(G)*. However, the influence is important only in the case of low distribution coefficients: in the case of higher distribution coefficients this influence is negligible. This conclusion is also true for small changes in the sample volume in duplicate analyses: exact reproducibility of the sample volume is important only in the case of low distribution coefficient values.