The HI4104 calcium ion 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 chloride electrolyte. The internal elements are isolated from the sample by an organic polymer sensing membrane.
Hanna’s liquid membrane 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 HI4104 to measure calcium accurately, it is important that the ionic strength of the standards and sample be adjusted to a high and constant value with the calcium ionic strength adjuster (ISA) solution. The ISA ensures that the activity coefficient is constant so the concentration of free calcium ions can be measured. Measuring all solutions with a constant ionic strength reduces the margin of error between measurements. The HI4104 calcium liquid membrane ISE can measure from 3µM (0.12 mg/L) to 1M (40,080 mg/L).
Conversion Table for Ca2+
moles/L (M) to ppm (mg/L)
ppm (mg/L) to M (moles/L)
2.49 x 10-5
Replaceable Sensing Modules - Combination liquid membrane ISEs are electrodes that detect free ions in a solution. This type of ISE is designed to incorporate easy replacement of the sensing module.
Durable PEI Body - The probe body is composed of durable polyetherimide (PEI) plastic.
BNC Connection - The HI4104 has a universal BNC connector for easy connection to any benchtop meter with a female BNC probe input.
Theory of OperationA liquid membrane ion selective electrode develops a voltage due to the ion exchange that occurs between the solution and the polymer membrane that contains organic ion exchange resin. 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.
Description combination Measurement Range calcium (Ca2+) 1.0M to 3•10-6M, 40,080 to 0.12 mg/L (ppm) Temperature Range 0 to 40 °C Body Material PEI/PVC Optimum pH Range pH 4 to 10 Body Length/Overall Length 120 mm Outer Diameter 12 mm Cable coaxial; 1 m (3.3’) Connector Type BNC Notes Approximate Slope +28 mV
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