Abstract: Under the optimal experimental conditions of three-phase hollow fiber liquid-phase microextraction (3p-HFLPME), the behaviors of hydroxybenzoic acids (HBAs) were investigated. The correlativities between the enrichment factor (EF) of HBAs and their n-heptanol/water conditional distribution coefficients (log Pn-heptanol/5 mmol/L HCl), pKa and the number of ~OH (N); the extraction mechanism that polyvinylidene difluoride hollow fiber contributed to promote the extraction efficiency by forming charge transfer compound with HBAs and the organic solvents showed notable selectivity for HBAs were elucidated. The optimal 3p-HFLPME conditions were: MOF 503 polyvinylidene difluoride hollow fiber as organic solvent supporter, n-heptanol as organic phase, 5 mmol/L HCl in the donor phase and 80 mmol/L NH3·H2O as the acceptor phase, the HBAs were extracted for 35 min under an agitation of 1200 r/min. It was found that the relative standard deviations were lower than 3%, the detection limits were 0.09~30.00 μg/L, the average recoveries of HBAs in Calyx Kaki were 93.3%~107.1% and the EF of HBAs at 5 mg/L was up to 107.6 fold.

Key words: charge transfer compound , enrichment factor, hydroxybenzoic acids, polyvinylidene difluoride hollow fiber, three-phase hollow fiber liquid-phase microextraction