Ion Concentration Measurement (ISE)

Perform your ion concentration measurements rapidly and accurately

Ion concentration measurement or ion-specific (ISE) measurements can be performed in every laboratory for a variety of sample types including water, food and beverage, pharmaceuticals, and biological samples.

To evaluate a sample's ion-specific performance, the best resource is slope S, also known from pH measurement. Whether you're looking to test ISE measurements through the direct method, dilution method, matrix match method, known addition method, or matrix factor method, our robust portfolio of ion-specific meters, electrodes, standards, and solutions are known for delivering accurate and reproducible ISE measurement results.

The ion selective electrode (ISE) is a useful and versatile sensor for testing ions in various types of samples, such as environmental, agricultural, industrial, biotechnical, pharmaceutical, food, wastewater, drinking water, and others. Typical ions of interest include ammonia, fluoride, nitrate, chloride, calcium, sodium, potassium, silver, sulfide, iodide, bromide, lead, cadmium, copper, and others.

How does the sample type affect the ISE method that I use for testing?

• Dilute aqueous (water) samples: Typical dilute aqueous (water) samples can be tested by simple, direct testing. Direct testing involves adding ionic strength adjuster (ISA) solution to standards and samples, calibrating with the standards, and testing the samples.
  
  
• Complex or high ionic strength samples: Some sample types are not dilute aqueous solutions. Samples that are complex or have a high ionic strength background may require a different approach than the direct test method to obtain the best results. In general, high ionic strength samples are samples of >0.1M concentration of dissolved ions or samples that may have a conductivity reading of greater than about 10 mS/cm.

Examples of dilute aqueous samples

Examples of complex or high ionic strength samples

To make an accurate measurement using an ISE, a suitable ISE method should be selected according to specific sample conditions.

• For complex or high ionic strength samples, addition of ISA may not be sufficient to normalize the ion's activity between the samples and the standards. In that case, choosing an alternate ISE method is recommended for accurate measurements.
   

What if my sample is a solid or is non-aqueous (not water-based)?

• A solid sample must be prepared so that the ion of interest is dissolved or extracted into water. For example, a certain type of powder, salt, or tablet sample might be mixed with water to dissolve the ion of interest prior to ISE testing. A soil sample may be dried, crushed, and/or sieved, then extracted into a water or salt solution prior to ISE testing. The extracting solution is chosen to bring the ions of interest into solution, and the extracting solution must not interfere with the ISE test.

• A non-aqueous liquid sample must be prepared so that the ion of interest is extracted into water. For example, an oil sample might be mixed with water or other extracting solution to extract the ion of interest into the water phase. The water phase is then tested. Alternately, the non-aqueous sample might be ashed or subjected to an oxygen combustion bomb preparation (e.g., EPA SW-846 Test Method 5050) to remove the organic matrix. After combustion, the inorganic residue is mixed with water and tested for ions. In some cases, the solid or viscous sample can be added directly to a standard solution and can be tested by analyte addition or subtraction.

Meeting regulatory and compliance standards

Regulations vary between ion specific measurements, and it’s critical that you have instruments and electrodes that allow you to stay complaint with your industry standards. Below is a list of international standards for regulatory compliance requirements for a variety of industries.

Regulatory Requirements

International standards for regulatory compliance requirements: 

ISE measurement for a variety of applications

Meet your sample analysis challenges with a combination of Thermo Scientific meters, electrodes, standards, and solutions, ideal for use with the following applications. Click on an icon below to learn more about these products.