Colorimetric assay for methanesulfinic acid in biological samples.

We describe a simple colorimetric method to measure 30 to 300 microM concentrations of sulfinic acids in biologic samples. The procedure employs the coupling reaction of an aromatic diazonium salt (Ar--N = N+) with the sulfinic acids (RSOOH) to produce a colored diazosulfone derivative (Ar-N = N-SOOR), which can be selectively extracted into an organic solvent. Linearity as well as noninterference by liver homogenate, phenols, amines, and thousandfold or greater excesses of sulfate, thiol, and dimethyl sulfoxide is demonstrated. Sensitivity of the method is about 10 nmol per sample. Because methanesulfinic acid is the principal product of the action of hydroxyl radicals upon dimethyl sulfoxide, and because intact animals can tolerate dimethyl sulfoxide in millimolar concentrations, the method may prove widely useful for detecting the involvement of hydroxyl radicals in pathologic processes in vivo.