Spectrophotometric determination of tin(II) by redox reaction using 3,3′,5,5′-tetramethylbenzidine dihydrochloride and N-bromosuccinimide

A rapid, straightforward spectrophotometric method based on the redox reaction of tin(II) with a mixture of N-bromosuccinimide (NBS) and 3,3′,5,5′-tetramethylbenzidine dihydrochloride (TMB) was developed for determining low concentrations of tin(II). The redox method improved sensitivity by 2.3-fold relative to the existing spectrophotometric methods by titrating tin(II) into an equimolar solution of colorimetric reagent TMB and oxidant NBS buffered with acetate to pH between 4.0 and 4.4 at 25°C. The spectral absorption at 452 nm was linear with respect to tin(II) concentration between the limit of quantitation (LOQ, 10σ) of 0.05 and 0.34 μg/mL over which a response curve was generated (R² = 0.9981, n = 7). The limit of detection (LOD) was calculated (3σ) at 0.01 μg/mL. Deviation between actual and measured concentrations varied from 0.014 μg/mL near the LOQ to 0.042 at 0.255 μg/mL.