Liquid chromatographic detector for organosulphur compounds based on a ligand-exchange reaction

A method is described for the post-column reaction detection of organosulphur compounds in liquid chromatography, which is based on a ligand-exchange reaction between the palladium(II)-calcein complex and the sulphur-containing compounds. The release of free calcein provides an indirect measure of the amount of organosulphur compounds via fluorescence detection. The kinetics of the reaction and the signal intensity have been studied as a function of the structure of selected organosulphur compounds and of parameters such as carrier- and reagent-stream composition and temperature. Optimal conditions are as follows: an aqueous mobile phase of pH 5-7, to which may be added up to 20% of methanol; an elevated reaction temperature of around 60 degrees C and a palladium(II)-calcein reagent solution of ca. 10(-5) M, which should contain some zinc(II) to enhance the fluorescence intensity. Detection limits, which are dependent on the structure of the compounds, typically are between 0.5 and 1.0 ng. Good linearity is observed over a two- to three-order concentration range. The method has been applied to the determination of ethylene thiourea in e.g. wash-water of apples and tomatoes, and to the detection of penicillamine in spiked serum and urine.