The HI4009 cyanide selective electrode is a potentiometric half-cell sensor housed within an epoxy body. The internal elements are isolated from the sample by a compressed silver halide sensing 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 HI4009 to measure cyanide accurately, it is important that the ionic strength of the standards and sample be adjusted to a high and constant value with the cyanide ionic strength adjuster (ISA) solution. The alkaline ISA ensures that the activity coefficient is constant so the concentration of free cyanide ions can be measured. Measuring all solutions with a constant ionic strength reduces the margin of error between measurements. The HI4009 cyanide solid state ISE can measure from 1µM (0.026 mg/L) to 0.01M (260 mg/L).
Conversion Table for CN–
moles/L (M) to ppm (mg/L)
2.602 x 104
ppm (mg/L) to M (moles/L)
3.843 x 10-5
Fixed Sensing Modules – Solid state half-cell ISEs are electrodes that detect free ions in a solution. The highly insoluble, compressed sensing pellet is attached to the HI4009 cyanide half-cell by a fixed sensing module for ease of use.
Durable Epoxy Body – The probe body of the cyanide half-cell ISE is composed of durable epoxy resin.
BNC Connection – The HI4009 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 ISA, the voltage is proportional to the concentration of free ions in solution.