Extraction-Chromogenic System for Silver(I) Based on Tetrazolium Violet and Semicarbazide Hydrochloride

Abstract

In the presence of semicarbazide hydrochloride (SCH) and traces of AgI, the tetrazolium salt 2,5-diphenyl-3-(1-naphmyl)-2H-tetrazolium chloride (Tetrazolium violet, TV) is reduced in alkaline medium to intensely colored chloroform-extractable 3,5-diphenyl-1-(1-naphthyl)formazan (Tetrazolium violet formazan, TVF). The following experimental parameters have been examined for finding optimal conditions for color development and extraction-spectrophotometric determination of AgI: concentration of reagents, extraction time, volume of the two phases, presence of dissolved oxygen, and light. Under the optimal conditions (cTV = 4.0 × 10−5 mol/dm3, cSCH = 2.4 × 10−3 mol/dm3, cNaOH = 4 × 10−1 mol/dm3, Vaq.phase = 25 cm3, Vchloroform = 4 cm3, extraction time t = 5 min) an isomer of TVF with λmax = 511–512 nm is predominantly extracted. The calibration curve (at 512 nm) is linear in the concentration range of 0.013–0.028 µg cm−3 of AgI. The following ions do not interfere in determination of 0.65 µg of AgI; Li+, Na+, K+, $$\rm{NH}_4^+$$, $$\rm{H}_2PO_4^-$$, F−, Cl−, $$\rm{SO}_4^{2-}$$, $$\rm{B}_4O_7^{2-}$$, $$\rm{ReO}_4^-$$, tartrate, and citrate (5000-fold excess); MgII and EDTA (1000-fold excess); PbII and BaII (500-fold excess); AlIII (300-fold excess); ZnII and CaII (100-fold excess); VV (50-fold excess); HgII, HgI, MoVI and FeIII (25-fold excess); and CuII and WVI (10-fold excess). CrIII interferes in the process at a mass ratio of 1 : 1, however small amount of this cation (1.5-fold excess) can be masked by EDTA.