Recrystallise the disulfide from H2O, EtOH, Me2CO, *C6H6 or pet ether. It has been used as a 1mM solution in EtOH for the spectrophotometric estimation of thiols. Essentially the thiol displaces half the disulfide molecule liberating the 4-mercaptopyridine (4-pyridinethiol) anion, thereby shifting the max from 324nm (of the disulfide) to 285nm (of the anion) at pH 9. (Compare with 2,2’dipyridyl disulfide above which has been used for the same purpose.) [Humphrey et al. Anal Chem 40 698 1970, Cheng & Ritchie Aust J Chem 26 1785 1973.] [Beilstein 21 II 35, for review see Aldrichimica Acta 4 33 1971.]
