Precautions when measuring the pH value of non-aqueous solutions
Non-aqueous solutions have poor conductivity, and a large and unstable liquid junction potential will form between the reference electrode and the solution being measured, resulting in considerable measurement errors. The reference electrode and the pH glass electrode should be as close as possible, and the penetration amount of the reference electrode electrolyte KCL should be larger (the penetration amount of the external reference electrode electrolyte KCL should be larger). It is best to use a composite electrode. Since the indicator electrode and reference electrode in the composite electrode are close and fixed, which is conducive to obtaining a stable and repeatable potential in non-aqueous solutions, the pH measurement cell should be well shielded.
When measuring emulsion or oil solutions, it is very important to correctly select the type of liquid junction and make it easy to renew and clean. It is recommended that open or sleeved liquid junctions be suitable for certain non-aqueous solution measurements.
When measuring online, strictly control the flow rate (laminar flow). Avoid turbulence.
The solvent of the reference electrode solution should be based on the measured solution composition to eliminate unstable liquid junction potential or use a double salt bridge solution.
After measuring non-aqueous solutions, the response characteristics of the pH glass electrode often decrease. At this time, the electrode should be cleaned with a cleaning agent, and then immersed in 0.1mol/LHCL for several hours to restore the electrode.
After measuring solutions containing fat and protein, the electrode can be immersed in a mixed solvent containing strong pepsin (Pepsin) HC for several hours, and then rinsed with water.
For the pH measurement of non-aqueous media similar to water, such as heavy water and water-alcohol systems, glass electrodes can maintain potential stability for a longer period of time in such solvents. The electrode is immersed in the solvent until the electrode reaches equilibrium, and then the standard buffer prepared with this solvent is used to calibrate the electrode. The pH value measured by this method is the relative pH value or apparent pH value.
For non-aqueous solution pH measurement electrodes, it is best to use lithium glass electrodes instead of soda glass pH electrodes (lithium glass pH electrodes are blue, and soda glass pH electrode bulbs are white). Because for glass electrodes, water must be present to form a "hydrated gel layer" with pH response, lithium glass electrodes have much smaller water requirements than soda glass electrodes.
For non-water measurements, a large-range pH meter should be used (beyond the full pH range of 14)
