Hanna Instruments offers a wide variety of pH electrodes that are designed for many different applications. The type of glass used for sensing pH, bulb shape, body material, type of junction, type of reference and electrolyte used are just some of the design considerations.
The HI12923 uses low temperature (LT) glass, conic bulb, glass body, triple ceramic junction, and is refillable with 3.5M KCl + AgCl.
Low Temperature Glass Formulation
The glass tip uses a special LT glass formulation with a lower resistance of approximately 50 megaohms compared to general purpose (GP) with a resistance of about 100 megaohms. As the temperature of the glass decreases when in a sample at low temperature, the resistance of the LT glass will increase approaching that of GP glass at ambient temperatures. If using GP glass, the resistance would increase above the optimum resistance for the high impedance input of a pH meter.The HI1292D is suitable to use with samples that measure from -5 to 70℃.
The conical shaped tip design allows for penetration into solids, semi solids, and emulsions. The HI12923 is ideal for the direct measurement of pH in soils and soil slurries.
The glass of the HI12923 is resistant to many harsh chemicals and is easily cleaned. The glass body also allow for a fast transfer of heat to the internal reference electrolyte. The mV generated by the reference cell is temperature dependent. The faster the equilibrium the steadier the reference potential.
Triple Ceramic Junction
The triple ceramic junction allows a higher flow rate of electrolyte from the reference cell into the measurement sample. A typical pH electrode will have a single ceramic junction that flow rate of 15 to 20 µL/hour. The HI12923 has three ceramic junctions in contact with the sample providing for a flow rate of 40 to 50 µL/hour. The increased flow provides a greater continuity between the reference electrode and the indicating electrode.
The HI12923 is a refillable probe. Since it is a single junction pH electrode the fill solution is the HI7071 3.5M KCl + AgCl. If using a refillable pH electrode, the fill cap should be removed prior to calibration and measurement. Removing the cap creates positive head pressure in the reference cell allowing for higher flow rate of electrolyte through the outer junction. A higher flow rate will result in a faster and more stable reading.
The HI12923 has a quick connect DIN connector that can be used with the HI99121 portable pH/temperature meter for direct pH measurement in soil.