Radon Binding to Water-Soluble Cryptophane

In previous work, other noble gasses, e.g. xenon, were found to have a high affinity for this water-soluble cryptophane.  It exhibited better Xe binding (K_A @ 3 x 10⁴ M^-1 at 310 K) than any previously described compound.  A similar result for radon would have significant metrological implications. Many radium (²²⁶Ra, ²²⁸Ra, etc.) and radon (²²⁰Rn, ²²²Rn, etc) assay procedures are conflicted because of the volatility of radon from solutions.  For example, this seriously restricts the ability to perform ion chamber measurements and gamma-ray spectrometry of sealed solution ampoules. A way to keep the radon bound in a solution would be a major breakthrough. The present cryptophane experiments, conducted at NIST with cryptophane syntheses from UPenn, were performed using a ²²⁶Ra-encapsulated generator as the source of ²²²Rn. The thermodynamic binding parameters would be extracted from differential measurements obtained by liquid scintillation counting of aliquots from reaction vessels. The first experiments, although yielding somewhat promising results, were not entirely successful because of experimental difficulties resulting from a radium breakthrough in the generator and the attendant ambiguities in data interpretation. A new series of experiments will be conducted shortly using a revised generator that has been constructed and with changes to the experimental design that has been incorporated into the protocol.