result = []
for ss in self.coupledIsotopeCodes:
if ss[-2] in '0123456789':
firstLetter = -1
else:
firstLetter = -2
atomSymbol = ss[firstLetter:].capitalize()
massNumber = int(ss[:firstLetter])
result.append(ccp.api.molecule.ChemElement.Isotope.getByKey(self.root.currentChemElementStore, (atomSymbol, massNumber)))
#
result = frozenset(result)