A sensitive method for the determination of long-chain fatty acids (LCFAs) (>C20) using 1-[2-(p-toluenesulfonate)-ethyl]-2-phenylimidazole-[4,5-f]-9,10-phenanthrene (TSPP) as tagging reagent with fluorescence detection and identification with post-column APCI/MS has been developed. The LCFAs in bryophyte plant samples were obtained based on distillation extraction with 1:1 (v/v) chloroform/methanol as extracting solvent. TSPP could easily and quickly label LCFAs at 90 degrees C in the presence of K2CO3 catalyst in DMF. Eleven free LCFAs from the extracts of bryophyte plants were sensitively determined. Maximal labeling yields close to 100% were observed with a five-fold excess of molar reagent. Separation of the derivatized fatty acids exhibited a good baseline resolution in combination with a gradient elution on a reversed-phase Eclipse XDB-C8 column. Calculated detection limits from 1.0 pmol injection, at a signal-to-noise ratio of 3, were 26.19-76.67 fmol. Excellent linear responses were observed with coefficients of >0.9996. Good compositional data were obtained from the analysis of the extracted LCFAs containing as little as 0.2g of bryophyte plant samples. Therefore, the facile TSPP derivatization coupled with HPLC/APCI/MS analysis allowed the development of a highly sensitive method for the quantitation of trace levels of LCFAs from biological and natural environmental samples.