On-line coupling of reversed-phase microcolumn liquid chromatography (micro-RPLC) and sulfur-selective flame photometric detection (S-FPD) was studied for the selective and direct determination of thiodiglycol, bis(2- hydroxyethylthio)methane, 1,2-bis(2-hydroxyethylthio)ethane, 1,3-bis(2- hydroxyethylthio)propane, and 1,4-bis(2-hydroxyethylthio)butane, which are breakdown products of the chemical warfare agents called sulfur mustards. Both isocratic and gradient elution were used. To improve sensitivity, large- volume injections were applied together with peak compression by displacement for late-eluting analytes. With S-FPD, detection limits of 1 μg/mL were obtained for all compounds. Using the same approach, the target analytes as well as various oxidation products could be identified by micro-RPLC with electrospray ionization mass spectrometry (ESI-MS) and ESI-MS/MS. The optimized micro-RPLC-S-FPD system was successfully used for the analysis of a spiked soil sample.