Sequential Titrimetric and Spectrophotometric Determinations of Trace Amounts of Tin(II) and Tin(IV) by Amplification Reactions

摘要

Two simple and accurate titrimetric and spectrophotmetric methods have been developed for the determination of tin. The methods were based upon the oxidation of tin to tetravalent tin with sodium periodate at pH 2.2-3.5; excess periodate ions were then masked with 5% sodium molybdate at the same pH. The released iodate ions were determined spectrophotometry (at 350 nm) as triiodide after the addition of KI. This proposed procedure offered a six-fold amplification for each tin(II) ion. Alternatively, the released iodine was extracted with chloroform and shaken with an aqueous solution of 1% (w/v) sodium sulfite. The iodide ions produced in the aqueous phase were then oxidized with sodium periodate after removing the unreacted sodium sulfite by boiling with H_2SO_4 (2M). The released iodate was finally determined by iodometry or spectrophotometry. This procedure offered 144-fold amplification per tin(II) ion. The determination of tin(IV) after prior reduction to tin(II) with sulfur dioxide was also found to be suitable. Analyses of the binary mixtures of tin(II)-tin(IV) in an aqueous solution, tin in organotin compounds and tin(II) and tin(IV) in artificial sea-waters were successfully carried out.