The HI4112 lead/sulfate 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 lead 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.
For the HI4112 to measure lead accurately, it is important that the ionic strength of the standards and sample be adjusted to a high and constant value with the lead ionic strength adjuster (ISA) solution. The ISA ensures that the activity coefficient is constant so the concentration of free lead ions can be measured. Measuring all solutions with a constant ionic strength reduces the margin of error between measurements. The HI4112 lead/sulfate solid state ISE can measure from 1µM (0.21 mg/L) to 0.1M (20, 700 mg/L).
The HI4112 can also be used as an indicator to follow the progress and detect the endpoint of a precipitation titration of sulfate. During the titration, the lead/sulfate ISE follows the lead concentration while a lead perchlorate solution is used to titrate the sample. The lead in the titrant solution reacts with the sulfate ions present in the sample to form a precipitate. Once all of the lead and sulfate ions have reacted, a change in mV occurs to signal the endpoint, and ultimately the sulfate concentration.
Conversion Table for Pb2+
|
Multiply |
|
|
moles/L (M) to ppm (mg/L) |
2.072 x 105 |
|
ppm (mg/L) to M (moles/L) |
4.826 x 10-6 |
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 HI4112 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.
