Silver/Sulfide Combination Ion Selective Electrode (ISE)

The HI4115 silver/sulfide selective electrode is a complete potentiometric cell that contains a silver/silver chloride (Ag/AgCl) reference housed within a PEI plastic body with a potassium nitrate electrolyte. The internal elements are isolated from the sample by a compressed silver/silver sulfide sensing 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.

Measuring all solutions with a constant ionic strength reduces the margin of error between measurements. The HI4115 silver/sulfide solid-state ISE can measure silver from 1µM (0.11 mg/L) to 1M (107,900 mg/L) and sulfide from 0.1µM (0.003 mg/L) to 1M (32,100 mg/L).

Silver (Ag⁺)

For the HI4015 to measure silver accurately, it is important that the ionic strength of the standards and sample be adjusted to a high and constant value with the halide ionic strength adjuster (ISA) solution. The ISA ensures that the activity coefficient is constant so the concentration of free silver ions can be measured.

Conversion Table for Ag⁺

	Multiply
moles/L (M) to ppm (mg/L)	1.0787 x 105
ppm (mg/L) to M (moles/L)	9.27 x 10-6

 

Sulfide (S^2-)

For accurate sulfide measurement, it is important that sulfur is released from hydrogen and that sulfide oxidation is prevented with the sulfide antioxidant buffer solution (SAOB). The SAOB ensures that the solution pH is above pH 12, reducing the effect of interfering ions and releasing sulfur from hydrogen ions. SAOB also acts to stabilize the activity coefficient so the concentration of free sulfide ions can be measured.

Conversion Table for S^2-

	Multiply
moles/L (M) to ppm (mg/L)	3.207 x 104
ppm (mg/L) to M (moles/L)	3.12 x 10-5

 

Features at-a-glance

Fixed Sensing Modules

• Combination solid-state ISEs are electrodes that detect free ions in a solution. The highly insoluble, compressed sensing pellet is attached to the electrode by a fixed sensing module for ease of use.

Durable PEI Body

• The probe body is composed of durable polyetherimide (PEI) plastic.

BNC Connection

• The HI4115 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.