Determination of the PKa of a Hyperpolarized H13CO3- PH Probe

Introduction: Tissue pHe can be determined using C MRS and hyperpolarized C-labelled bicarbonate (HCO3). Using an assumed pKa, the HCO3 and CO2 signal intensities allow pH determination using the Henderson-Hasselbalch equation. With a view to future clinical application we compared pH derived by DNP NMR with direct potentiometric measurement of H activity using a glass electrode. Using pKa = pH – log ([HCO3]/[ CO2]), we assigned the pH determined potentiometrically as the standard and determined whether the C MRS derived pKa diverges when there is alteration of ionic strength (I), pH, temperature and protein concentration within a clinically relevant range of values. Additionally, the pKa in human blood was determined.