A New Single-Solution Confirmatory Test for Nitrite Ion Mereaptoacetic acid, HSCH&OOH, is a highly selective reagent for confirmation of nitrite ion, in anion qualitative analysis schemes in general chemistry and elsewhere. A few drops of a 1%aqueous solution of mercaptoacetic acid, added to 0.5 rnl of a 1%solution of sodium nitrite, causes immediate development of a characteristicsalmon a h . The color results from faimation of an S-nitrosocompound, ageneral reaction of mercaptans; the carhoxyl group in the r.eagent supplies the acid necessary for the reaction, all in a single solution. None of the other anions in our qua1 scheme (sulfide, sulfite, sulfate, thiosulfate, carbonate, acetate, oxalate, borate, nitrate, fluoride, chloride, brmnide, iodide, and phosphate) shows any reaction with mercaptoacetic acid, nor do any of the common laboratory acids and bases. Nitrite ion may he &firmed in the presence of other anions. Even the oxidizable anions do not interfere, as nitrite is a sluggish oxidizing agent at this amcentration of acid. In particular, iodide wesents no problem. The salmon color of the nitrite test aooears lone before the darker hrown of free i"dine is noticeable, and the eoiors are quite different in any ease. A 1%soluti;,; of mercaptoaeetic acid has a mild mercaptan odor (like HrS), but presents no toxicity hazard at this concentration. The reagent is inexpensive, and the adution appears to have an indefinite shelf life.
I'urdur Cnivrrsil, North Central l'arnl~us
R. M. Hawthorne, Jr. M. J. Ruthenberg
Writville, Indiana 16391
Volume 55,Number 1, January 1978 / 29
