Acid-base properties of human gingival crevicular fluid

The pH of human gingival crevicular fluid (GCF) has been reported by many authors to be very alkaline (pH 7.5 - 8.7). This alkalinity could be explained, at least partially, by the fact that all measurements were performed either at low PCO2 or in the absence of CO2. Therefore, we set up a procedure which allows for measurement of the pH of GCF samples from single inflamed sites at controlled PCO2. At a PCO2 of 4.7 kPa (= 35 mmHg) and at 37 degrees C, the pH was 7.96 +/- 0.10 (SEM, n = 9), a value which differs significantly from the value of 8.38 +/- 0.09 measured in the absence of CO2 in the same samples. The non-bicarbonate buffer value of the sample determined by CO2 titration was 6.0 slykes. It is because this value is low that pH varies so greatly with PCO2. At physiological PCO2, the total buffering power becomes very high above pH 8.0, because of the high bicarbonate concentration.