Intracellular pH as measured by 19F NMR.

19F NMR pH measurements with the fluorinated pH indicators we have described are rapid and sensitive, work with readily available commercial instruments, and extend the applicability of nondestructive NMR measurements to systems for which 31P NMR measurements are presently impractical. The family of 19F pH indicators is useful for independent confirmation of pHi values obtained by 31P NMR, distribution of radioactive weak acids, or other methods. The necessity for using exogenous indicators, which at first appears as a liability, can be turned to advantage also. Our future goal is to direct our measurements unambiguously to compartments (in cells or in tissues) of particular interest, by matching the indicator precursor molecule to the hydrolytic enzyme activities inherent in the target cell or compartment, so that the pH indicator is generated in situ.