Separation and Preconcentration of Bismuth, Lead, and Antimony in Steel-digested Solution by Ion-exchange Adsorption Followed by Ion-pair Elution

A unique preconcentration technique for anionic species referred to “ion-exchange preconcentration followed by ion-pair elution” was applied to separation and preconcentration of trace amounts of bismuth, lead, and antimony in digested solutions of iron and steel. First, these elements in the digested solutions were derived to anionic iodo complexes with iodide ions under an acidic condition prior to preconcentration. The derived anionic complexes were adsorbed on the anion exchanger made of cotton and trioctylmethylammonium chloride (referred to capriquat), followed by being recovered as ion-pairs of capriquat by elution with methanol. On the other hand, iron matrices did not adsorb on the anion exchanger because the iron matrices in the digested solution were reduced into divalent state with ascorbic acid not to form iodide complexes. More than 99.99% iron could be removed by rinse with a solution containing 0.8 mol dm−3 ascorbic acid and 0.5 mol dm−3 hydrochloric acid. Subsequently, the concentrates were analyzed by graphite furnace atomic absorption spectrometry. Preconcentration with 5-fold enrichment allowed us to determine trace amounts of bismuth, lead, and antimony in a digested solution of iron with detection limits (3σ) of 4.4×10−9 mol dm−3, 5.3×10−9 mol dm−3, and 3.0×10−8 mol dm−3, respectively.