Determination of micromolar concentrations of strong acids in chloroform by protonation of tetraphenylporphyrin
The protonation of tetraphenylporphyrin followed by spectrophotometric detection of the resulting dihydrogen tetraphenylporphyrin dication has been evaluated as a means to determine micromolar concentrations of strong acids in chloroform. The equilibrium constants for the process are large (>1010 for benzenesulfonic and methanesulfonic acids), but not large enough to ensure stoichiometric conversion to the dication unless only order of magnitude precision is required. The incorporation of a correction term in the stoichiometric approximation, based on a dilution of the analytical sample, yields an acceptable result for these two acids.
Brent M. Harvey and Patrick E. Hoggard, “Determination of micromolar concentrations of strong acids in chloroform by protonation of tetraphenylporphyrin”, Monatshefte Chem. 143, 1101-1105 (2012).