Kinetic determination of trace amounts of thiosulfate based on its inhibitory effect

Abstract

The sulfur containing ligand viz., thiosulfate is found to inhibit the Ag(I) catalyzed substitution of cyanide in hexacyanoferrate(II) by phenylhydrazine. The inhibitory effect of thiosulfate is attributed due to its tendency to form complexes with Ag(I), leading to the production of inhibitor-catalyst complexes. The reactions, followed spectrophotometrically in aqueous medium at 488 nm, was possible by the increase in absorbance of the cherry-red product, [Fe(CN) 5 PhNHNH 2 ] 3-at pH 2.8 (±0.02), at 30 (±0.1) °C, and an ionic strength (μ) of 0.02 M (KNO 3 ). The linear calibration curves were obtained using the absorbance measured at different times (A t ) and thiosulfate concentrations under specified conditions. The calculated detection limit was 4.9 × 10 -7 M. The Michaelis-Menten constant (K m ) and equilibrium constants for the formation of complexes between catalyst and inhibitor (K CI ), and the catalyst and substrate (K S ) were computed from the kinetic data. A general mechanistic scheme is proposed for this reaction.

Extraction, preconcentration and spectrophotometric determination of trace levels of thiosulfate in environmental waters

“…Thiosulfate determination has been mostly performed using analytical techniques such as flame-containing molecular emission cavity analysis (MECA) [30], kinetic spectrophotometry [31], gas chromatography-mass spectrometry (GC-MS) [32], flame atomic absorption spectrometry (FAAS) [33], high-performance liquid chromatography (HPLC) [34], ion-pair chromatography with ultraviolet absorbance [35], ion chromatography (IC) based on isocratic elution with fluorescence detection [36] and inductively coupled plasma mass spectrometry (ICP-MS) [37]. Determination of thiosulfate via these methods is expensive, tedious and time-consuming as well as poor precision at low concentrations and requires expert user in her/his area.…”