Mass transfer resistance in a liquid-phase microextraction employing a single hollow fibre under nonsteady-state conditions

In this study, the mass transport resistance in liquid-phase microextraction in a single hollow fibre (HF-LPME) was investigated. A mathematical model has been developed for the determination of the overall mass transfer coefficient based on the acceptor phase, KA, in an unsteady-state HF-LPME. KA in HF-LPME has been estimated from time-dependent concentration of extracted analyte in the acceptor phase while maintaining a constant analyte concentration in the donor phase. It can be achieved either using a high volume of donor to acceptor phase ratio or tuning the extraction conditions to obtain a low enrichment factor, so that the analyte concentration in the sample is not significantly influenced by the mass transfer. Two HF-LPME systems have been used to test experimentally the developed model: the extraction of Lu(III) from a buffer solution and the extraction of three local anaesthetics from a buffer or plasma solution. The mass transfer resistance, RA, defined as a reciprocal values of KA, was found to be 1.2103 cm-1 min for Lu(III) in HF-LPME under optimal conditions. The RA values for the local anaesthetics were in the range from 1.96 to 3.3 103 cm-1 min, depending on the acceptor pH and the hydrophobicity of the drug.