A new method for the separation and pre-concentration of butyl tin speciation with crosslinked chitosan (CCTS) and for its determination by hydride generation atomic absorption spectrometry was developed. At pHs 6.8,4.4, and 3.0, monobutyl tin (MBT), dibutyl tin (DBT), and tributyl tin (TBT), respectively, were separated and preconcentrated with CCTS, eluted quantitatively with 10 mL of 1 mol L-1 HCl, and determined. The method was applied to the discrimination and determination of MBT, DBT, and TBT in water and sediment samples. The detection limits of TBT, DBT, and MBT were 21.2, 25.5, and 28.5 ng L-1, respectively. The analytical recoveries of MBT, DBT, and TBT added to the samples were 91-95%, for water samples and 82-90% for sediment samples. The results were satisfactory. (C) 2004 Wiley Periodicals, Inc.