Methods based on solid-phase reagents have been developed for detecting thiols, disulfides and proteolytic enzymes in liquid chromatography eluates. In each method, compounds in the class of interest released chromophoric reagent from the packing material in a short column just beyond the analytical column, and that reagent is then detected in an optical detectro. It is thus possible to eliminate mixing of the eluate with soluble reagents in mixing tees, the approach used in earlier methods for detecting these classes of compounds. The advantages and limitations of the solid phase approach in the present work are likely to attend attempts to apply the method to other detection problems in liquid chromatography. © 1979.