A kinetic method for the determination of organosulfur compounds by inhibition: determination of cysteine, 2,3-dimercaptopropanol and thioglycolic acid
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A kinetic method for the determination of organosulfur compounds by UV spectrophotometry is described. Organosulfur compounds have been shown to inhibit the Hg(II)-catalyzed substitution of cyanide in hexacyanoferrate(II) by 2-methylpyrazine (2-Mepz). The inhibitory effect is proportional to the concentration of inhibitor and can be used as the basis for the determination of trace amounts of organosulfur compounds such as cysteine, 2,3-dimercaptopropanol (DMP) and thioglycolic acid (TGA). Both the influence of the reaction variables and interference of a variety of ions have been studied. A mechanism for the inhibition process is proposed. The determination range depends on the amount of Hg(II) added and stability of the Hg(II)–ligand complex. Kinetic parameters were determined from Lineweaver–Burk plots, obtained in the absence and presence of the inhibitor. Excellent linearity is observed for all analytes over their respective concentration ranges with correlation coefficient >0.9. The condition calibration curves were linear in the range of 5 × 10−6–15 × 10−6 M for cysteine, 1 × 10−7–7 × 10−7 M for DMP and 1 × 10−6–10 × 10−6 M for TGA. The detection limits were 1.18 × 10−7 M for cysteine, 4.16 × 10−8 M for DMP and 1.30 × 10−7 M for TGA. The effects of amino acids that can interfere in the determination of cysteine were studied.
KeywordsHexacyanoferrate Thioglycolic Acid Organosulfur Compound Potassium Hydrogen Phthalate Potassium Hexacyanoferrate
Author is grateful to The University of the South Pacific, Suva, Fiji for providing financial and other necessary support to carry out this project. The author also wishes to sincerely thank Dr. Godwin Ayoko, School of Physical and Chemical Sciences Queensland University of Technology, Australia for reading and providing useful comments on the manuscript.
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