Pb Chemistry Overview
The purpose of this document is a quick primer in Pb chemistry, to briefly describe why certain stages are done and to warn about the potential pitfalls and mistakes that can be made along the way. Nd chemistry is broken into three different sets of columns, utilizing two different types of resin and several different reagents. For Pb separation, AG1X-8 resin is used to purify Pb from other metals in a sample.
One of the major cruxes of this chemistry is fully dissolving the sample in the loading acid. Samples are loaded onto the column in 1.1M hydrobromic acid, which does not do an efficient job of dissolving a HCl salt and bringing a sample into solution. Due to this, samples should remain in the loading acid at least overnight before column chemistry. It is preferable to let the samples sit several days in the acid prior to column chemistry, to ensure samples are in solution. Dilute hydrobromic acid is used as the loading acid because specific elements are considerably more strongly absorbed by anion exchange resins in this loading solution. Separation factors between the metals of interest and other metals in a rock are considerably larger when samples are loaded in dilute hydrobromic acid. Hydrochloric acid is used during cleaning and elution stages as its addition to the resin bed does not allow the resin to continue to binding to the metals of interest.
The procedure for Pb chemistry requires a sample to be run through the sample column chemistry twice. During primary separation Fe-Cu-Ni-Co and Pb may all be eluted from the column, however the goal is to purify the sample to Pb. A secondary separation, rerunning the sample elution through the same column chemistry, is efficient at further purifying the sample to Pb. The second round of column chemistry may be run directly after completion of the first round, although sample dry down and reprecipitation may take slightly more time than the prescribed rounds of column cleaning using 6M HCl. If this is the case, just continue to wash the columns with 6M HCl until the samples are ready for loading. This will ensure the resin does not dry out. Make sure to precondition the columns between column cleaning and sample loading (250 uL of 1.1M HBR). The second round of column chemistry can also be run at a later time if timing requires it.
For information on the resin chemistry and background of Pb chemistry, please see:
Strelow, F.W.E., 1978, Distribution coefficients and anion exchange behavior of some elements in hydrobromic-nitric acid mixtures: Analytical Chemistry, v. 50, p. 1359-1361.
Warren, J.M., Shirey, S.B., 2012, Lead and osmium isotopic constrains on the oceanic mantle from single abyssal peridotite sulfides: Earth and Planetary Science Letters, v. 359-360, p. 279-293.