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Ion Exchange Separation of Lead from Strontium in Certified Reference Samples and Spectrophotometric Determination of Lead as Extractable Ion-Pair of Eosin2− and the Lead–Cryptand (2.2.2)2+ Complex

Abstract A two-step procedure including anion exchange separation of lead from strontium in geological reference samples and a spectrophotometric determination of the separated lead as lead–cryptate (2.2.2) complex is presented. The exchangeable anion Cl− of the ion exchange resin (Dowex 1 × 4) is changed to Br− in 6 M HBr solution. Lead is quantitatively retained in the column from 0.5 M HBr medium, while Sr2+, Ba2+, Ca2+, Mg2+, Na+, K+, Fe3+, Cr3+, and Al3+ are passed through. Subsequently the retained Pb is eluted from the column with 6 M HBr. The separation efficiency of the resin is controlled using mixed standard solution of (Pb, Sr, Ca, Mg, Ba, Na, K, Fe, Cr and Al), and radioactive tracers of 85Sr and 131Ba. The resin selectivity coefficient (K) of separating Pb from Sr is found to be . The Spectrophotometric method of lead determination is based on the formation of lead–cryptate (2.2.2) complex at pH 8.3 using borate/HCl as a buffer solution. Then the ion-pair of eosin2+ and lead–cryptand (2.2.2) complex is extracted with chloroform, finally the absorbance of the extractable legend is measured at 550 nm. The extraction recovery, accuracy, precision, linearity and detection limit of the spectrophotometric method are 99.58%, 1.7%, 0.080 µg mL−1, 0–9 µg mL−1, and 0.060 µg mL−1, respectively.