When aqueous solutions of thioglycolic acid are equilibrated with sphaierite, a zinc sulfide mineral, a large fraction of the thioglycolic acid is either adsorbed on the sphalerite surface or oxidized to dithiodiglycolic acid. The total concentration of thioglycolic and dithioglycolic acid in solution has been determined by molecular emission cavity analysis (MECA). The fraction of the thioglycolic acid that Is not adsorbed on the mineral surface and remains in solution has been determined by a coulometric titration in which iodine is electrogenerated in situ and the end point located by an amperometric method. Attempts to determine the thioglycolic acid that was adsorbed on the mineral surface directly by MECA gave unreliable results. This has been attributed to the wide variation in the surface area as well as the surface chemical composition of small samples (1–2 mg) of the mineral that must be used in the sample cup in MECA. Thioglycolic acid also leaches traces of metal Ions from the mineral surface. The concentration of zinc( II) in solution reflects the extent of leaching that has occurred.
ASJC Scopus subject areas
- Analytical Chemistry