This paper describes the analysis of perchlorate (ClO4-) in surface water samples by a rapid and reliable ion-pair hollow-fiber liquid-phase microextraction (HF-LPME) method coupled with flow-injection electrospray ionization tandem mass spectrometry (ESI-MS-MS) technique. The effects of the type and concentration of ion-pairing reagents, extraction time, temperature and pH value on the quantitative extraction of perchlorate by ion-pair HF-LPME were investigated and optimized. Di-n-hexyl ammonium acetate (DHAA) was employed to form an extractable ion-pair complex with aqueous perchlorate. The characteristic ions [ClO4-ClO4-DHA](-) at m/z384.6 and 386.7 were observed in the ESI negative-ionization mode. The predominant product ions [ClO4](-) at m/z 99 and 101 were used for quantitation and to maximize the detection selectivity and sensitivity. The limit of detection (LOD) was 0.5 mu g/L. The reliability and precision of the standard addition method of ion-pair HF-LPME for the determination of trace levels of perchlorate in surface water were demonstrated. (C) 2009 Elsevier B.V. All rights reserved.