Solvent Extraction of Pb from Nitric Acid Solutions
Huffmann, Daniel P.
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Lead isotope ratios are useful in archaeological chemistry for tracing the origins of samples. In this study, a method is developed for the extraction of Pb from hone and teeth by a solvent extraction with 18-crown-6 ether and its variants. Effects of sample pH, ether concentration, stripping agent, and choice of crown ether are examined. Contacting either 4'4"(5")-di-tert-butyl- 18-crown-6 ether or dibenzo-18-crown-6 ether with a solution of Pb in RN03 and then stripping with EDTA causes recovery of~40% of Pb, depending on sample pH. 18-crown-6 ether and dicyclohexano-18-crown-6 ether recover at most ~5% and ~30%, respectively. Use of CHC13 in place ofa crown ether is less effective (~3% recovery), but much more economical. Attempts to strip Pb off of glass beads by soaking them in 1M HCl, H20, and 50% sat. EDTA solution show that HCl and H20 recover 9% and 17% less Pb, respectively, than EDTA. The optmized extraction procedure consists of contacting 4'4"(5")-di-tert-butyl-18-crown-6 ether or dibenzo-18-crown-6 ether in CHCl3 with a Pb sample dissolved in nitric acid. The Pb is then stripped from the organic phase with EDTA and analyzed.