Abstract: Anovel reserved-phase ion-pair liquid chromatographic method using hexadecyltrimethylammonium bromide(HTMAB) as an ion-pair reagent for separating the complexes of metal and 8-hydroxyquinoline-5-sulphonic acid(HQS) coupled with on-line fluorescence detection has been developed. The chromatographic behavior of metal-HQScomplexes in the proposed system was systematically investigated.When the C₁₈ column modified by HTMABand the suitable mobile phase coupled with fluorescence detection(λ_ex=388 nm; λ_em=518 nm) were employed, the detection limit of cadmium is 7.72 ng/mLwith an injection volume of 20 μL, and the linear range of calibration curve for cadmium is 50—800 ng/mL. It was successfully applied to determination of bio-available cadmium in polluted soils of China. Moreover, the possible species of Cd-HQSon the column has been investigated by log-log plot analysis.

Key words: Reversed-phase ion-pair HPLC, Bio-available cadmium, Hexadecyl trimethyl ammonium bromide, 8-Hydroxyquinoline-5-sulphonic acid