COMPARISON OF PH MEASUREMENTS MADE USING P-31 NMR AND A FIBEROPTIC PH-METER

The objective of this study was to compare pH measurements made in biological samples using P-31 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.