HI4110 – Fluoride ISE, Solid-state Combination

The HI4110 fluoride selective electrode is a complete potentiometric cell that contains a silver/silver chloride (Ag/AgCl) reference housed within a PEI/epoxy body with a potassium nitrate/potassium chloride electrolyte. The internal elements are isolated from the sample by a lanthanum fluoride crystal membrane. Hanna's solid state combination ISEs are designed with a cone style junction. The skirted cone geometry of the sensor 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 HI4110 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 HI4110 fluoride solid state ion selective electrodes can measure from 1µM (0.02 mg/L) to saturated F-. 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 Replaceable Sensing Modules Combination solid state ion selective electrodes are electrodes that detect free ions in a solution. The lanthanum fluoride crystal sensing membrane is replaceable and easy to attach to the sensor body. Durable PEI Body The probe body is composed of a mixture of polyetherimide (PEI) and epoxy. BNC Connection The HI4110 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.