Ninhydrin reaction on thiol-reactive solid and its potential for the quantitation of d-penicillamine

While aminothiols produce weak purple-colored reactions with ninhydrin, we demonstrate for the first time that this color could be intensely developed. Using a d-penicillamine paradigm, adsorption of this compound via a disulfide bond onto thiol-reactive solid prior to ninhydrin reaction allowed spectrophotometrical monitoring of the supernatant at 570 nm. Compared with off-solid method, this approach expanded the linear concentration range to 50-600 μg mL⁻¹ and enhanced the sensitivity so that d-penicillamine with the concentrations of less than 100 μg mL⁻¹ could be accurately quantitated by using a second-order polynomial calibration curve. Additionally, this assay was unaffected by disulfide adduct interference, highlighting its potential for the analysis of d-penicillamine as well as other aminothiols.