Fluoride ions exist predominantly as hydrofluoric acid in acidic environments with a pH below 5.2. Fluoride ions corrode the glass. Therefore, the pH measurement with the glass electrode for a solution which includes fluoride ions is basically impossible. Although the useful life of the electrode may be shortened, however, the measurement with immersing the electrode in the sample for a given short time is possible. Also, if the sample is basic, the glass may relatively be capable of resisting the use because the fluoride ions become the complex. Within the 5.2 to 10 pH range, fluoride ions do not corrode glass, so that pH measurement can be performed. At pH values above 12 however, the network structure of glass is broken up, forming complex molecules consisting of silica and fluoride ions and dissolving as SiF62-, so that pH measurement is not possible.

<Measure Procedure>

Perform the measurement using the composite electrode or the integrated electrode in an exceedingly shortened immersion time. Because the sensing part is immersed every measurement operation, calibration shall be performed for each measurement. After the measurement, wash the electrode system with 0.1mol/L HCl, and then rinse it sufficiently with pure water.

*Note: The useful life of the electrode may become extremely shorter than the usual use. 

We provide the following electrode for measuring the pH of samples containing hydrofluoric acid:
pH electrode for samples containing hydrofluoric acid (model: 9631-10D)
This product employs a thick glass membrane formation technology and a new responsive membrane, which make it more than 3 times as resistant to the acid in samples containing hydrofluoric acid as conventional products.