In vivo detection of a pH-sensitive nitroxide in the rat stomach by low-field ESR-based techniques.

A study was made of the in vivo detectability of a pH-sensitive, imidazolidine spin probe, and the efficacy of low-frequency electron spin resonance (ESR)-based techniques for pH measurement in vitro and in vivo in rats. The techniques used were longitudinally-detected ESR (LODESR) and field-cycled dynamic nuclear polarization (FC-DNP) for in vitro and in vivo measurements, and radiofrequency (RF)- and X-band ESR for comparisons in vitro. The spin probe was hexamethyl imidazolidine (HMI) with a pK of 4.