Comparison of pH measurements made using 31P NMR and a fibreoptic pH meter

Abstract

The objective of this study was to compare pH measurements made in biological samples using ³¹P NMR (pH_NMR) with those made with a novel, dye‐based fibreoptic pH measurement system (pH_F), which is compatible with use in electromagnetic fields without field perturbation. Using protein‐free model solutions, pH_NMR was calibrated against pH_F, giving a correlation coefficient of 0.969 and a mean difference (± SD) between pH_NMR and pH_F of 0.037±0.054 over the pH range 6.8–7.7. Further calibration of pH_NMR with pH_F was carried out for human red blood lysates and then pH_NMR was compared with pH_F for whole, packed red blood cells over the pH range 7.0–7.8. Values for pH_NMR, the intracellular pH, were consistently lower than for pH_F, the extracellular pH, by a mean (±SD) of 0.15±0.02 units. A close correlation of extracellular pH_NMR with pH_F was demonstrated for a blood sample exhibiting two P_i peaks, over the pH range 7.03–7.71. We conclude that concurrent use of NMR and the fibreoptic pH meter provides a reliable method of simultaneous measurement of intracellular and extracellular pH in biological systems.