The equilibrium constants (expressed in terms of their pK values) are commonly obtained experimentally from concentration measurements in relatively dilute equilibrium solutions or by their extrapolation to zero ionic strength, typically in conjunction with a Debye-Hückelrelated equation to model the species activity coefficients. Whereas the pK a of the amine deprotonation reaction R1 can be measured relatively accurately by means of potentiometric titration or by spectroscopic concentration measurements in a CO 2 -free solution, accurate determination of pK c for the carbamate reversion reaction R2 is more challenging due to the presence in a CO 2 -loaded solution of the coexisting species involved in the indicated set of reactions. In addition, due to the rapid proton exchange, NMR techniques cannot distinguish between the bicarbonate/carbonate species peaks or the amine/protonated amine species peaks, and only the sums of the relevant individual species concentrations in each pair can be determined. This has resulted in the use of different approaches to unravel the individual species concentrations from the NMR data. By relating the intensity of the two-species compound peak to the individual species peaks and their concentrations in the solution, amine and its protonated form may be distinguished by interpolation of the NMR chemical shifts at low and high pH values or by measuring the spectra of solutions that contain only the individual species. In addition, species at concentrations less than about 10 -4 molal are undetectable by the analysis of NMR data. These experimental challenges typically result in a significant uncertainty in the resulting carbamate reversion constant values, even for the well-studied monoethanolamine (MEA) system.