Automated multiple headspace extraction procedure: adsorption modeling and determination of air-to-water partition...

The present work makes the first attempt to take into account adsorptions in the determination of partition coefficients by modeling the multiple headspace extraction (MHE) process. Modeling a six-step MHE procedure of a homologous series of methyl ketones revealed that their adsorption-desorption on the walls was the rate-limiting step. Moreover, a comparison between experimental and predicted MHE plots shows that only the last MHE points were affected by adsorption phenomena. Using cell materials with the lowest sorptive properties, partition coefficients were then accurately calculated from the first four MHE steps. This kinetic approach supports previous work in which adsorptions were lowered owing to the choice of sampling cell materials. It also justifies some reproducibility limitations of the MHE quantification procedure mentioned in the literature.