COMPARATIVE MEASUREMENTS OF SALIVARY pH

¹ Foundation for Dental Research of the Chicago College of Dental Surgery, Chicago, Illinois

1. The drift of potential frequently encountered in measuring the pH of saliva by the quinhydrone method can be eliminated by the use of a vacuum tube potentiometer.

2. The salivary pH of 50 patients was measured by means of the glass and quinhydrone electrodes for purposes of comparison. The quinhydrone method usually gave slightly lower results, the greatest deviation being 0.13 pH units and the average for 50 measurements was about 0.08.

3. The differences in salivary pH as measured by the 2 methods was not constant for any one individual but varied from day to day.

4. Attempts to correlate the difference in pH by the 2 methods with oxidation-reduction potentials were unsuccessful because of the difficulties encountered in measuring the latter. From theoretical considerations, however, we can say that the deviation in pH by the quinhydrone method will probably be greater the farther removed the oxidation-reduction potential is from zero.