FC301B – pH Halbzelle

The FC301B fluoride selective electrode is a potentiometric half-cell that housed within an epoxy body. The internal elements are isolated from the sample by a lanthanum fluoride crystal membrane. This solid state sensor requires a separate reference electrode to complete the measurement system. Hanna's solid state half-cell ISEs are designed for use with the HI5315 reference half-cell. The reference half-cell features a cone style junction. The skirted cone geometry of the reference forms the liquid junction with the test solution at the tip of the junction cone, producing a highly stable reference potential and consistent flow rates of electrolyte into the solution. A simple press of the top portion of the ISE makes it easy to empty the electrolyte fill solution and replace when necessary. For the FC301B to accurately measure total fluoride concentration, it is important that the pH and ionic strength of the standards and sample be adjusted to a constant value. The total ionic strength adjustment buffer (TISAB) ensures that the solution pH is between pH 5 and 8 and that the activity coefficient is constant. The TISAB solution also preferentially complexes with various metal ions, such as aluminum and iron, which tend to form complexes with fluoride ions. TISAB thus ensures that these metal ions do not interfere, permitting an accurate total fluoride measurement. Measuring all solutions with a constant pH and ionic strength reduces the margin of error between measurements. The FC301B fluoride solid state ISE can measure from 1µM (0.02 mg/L) to saturated. Conversion Table for F- Multiply moles/L (M) to ppm (mg/L) 1.900 x 104 ppm (mg/L) to M (moles/L) 5.263 x 10-5 Features at-a-glance Fixed Sensing Modules - Solid-state half-cell ISEs are electrodes that detect free ions in a solution. The lanthanum fluoride crystal sensing membrane is attached to the FC301B fluoride half-cell by a fixed sensing module for ease of use. Durable Epoxy Body - The probe body of the fluoride half-cell is composed of durable epoxy resin. BNC Connection - The FC301B has a universal BNC connector for easy connection to any benchtop meter with a female BNC probe input. Theory of Operation A solid-state sensor electrode develops a voltage due to the ion exchange that occurs between the solution and the inorganic membrane. An equilibrium occurs due to the highly limited solubility of the membrane material in the sample. When the ionic strength of the solution is fixed by the addition of ionic strength adjuster, the voltage is proportional to the concentration of free ions in solution.