Determining simple sulfhydryl compounds (low molecular weight) and their contents in biological samples by using 2,2′-dithiobis-(5-nitropyridine)

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DTNP—2,2′-dithiobis-(5-nitropyridine)—was found to be useful for spectrophotometric determination of simple (low MW) -SH compounds and their contents in biological samples. Unlike 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB), DTNP can develop color with -SH compounds at the acidic or alkaline pH medium (pH 5.5–8.9). The developed color is stable and, therefore, suitable for analysis. DTNP was found to be more sensitive than DTNB (a widely used color reagent) for spectrophotometric determination of -SH compounds. A linear response, conforming to Beer's law, of absorbance readings to concentrations was observed for all the simple -SH compounds tested in the study. On a molar basis, once those -SH compounds reacted with DTNP, they gave essentially identical responses (within experimental errors). A high correlation was demonstrated between the spectrophotometric and amperometric methods for determining simple -SH contents in biological samples.