Philippe M. Heynderickx
Dynamic headspace sampling is a crucial technique for analyzing consumer products, studying biological samples, and conducting environmental water tests. Specifically, initial headspace concentrations are vital in forensic investigations and in calculating Henry coefficients. In the latter context, ‘initial’ refers to equilibrium with the liquid phase, where deviations are undesirable. However, during dynamic measurements, achieving true equilibrium is often challenging, leading to potential inaccuracies if only the initial concentration is considered.
This work examines how experimental parameters – such as sampling time, flow rate, headspace volume, liquid volume, and Henry coefficient – affect the measured average concentrations. A corresponding analytical expression, as a function of these variables, is introduced to quantify the deviation of the initial headspace concentration. A measurement accuracy criterion (error below 5%) is also provided. The model is a bi-exponential function that consolidates various existing models for recovery in dynamic sampling into a unified expression (Heynderickx, 2019).
Additionally, the developed model can be applied to determine Henry coefficients for gas compounds in non-ideal solutions through parameter estimation, allowing the effects of real liquid phase conditions to be inferred from gas phase measurements.
