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 FC220B uses low temperature (LT) glass, spherical 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. This is beneficial since many food products are stored at low temperatures. As the temperature of the glass decreases in the sample, 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 FC220B is suitable to use with samples that measure from 0 to 50°C.
Spherical Bulb
The spherical bulb is for general purpose use. Other tip shapes include conic for penetration and flat tip for surface measurements.
Glass Body
The glass body is ideal for laboratory use. The glass 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 FC220B 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, making it suitable for viscous solutions or samples of low conductivity, such as pure water.
Refillable
The FC220B 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.
BNC Connector
The FC220B uses a BNC connector. This type of connector is universal in that it can be used on any pH meter that has the female BNC probe input. Other type of connectors include DIN, screw type, T-type, and 3.5mm to name a few.
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