Ionenselektive Elektroden (ISE) - Theorie und Praxis

Ion-selective electrodes (ISEs) are a modern analytical tool for the fast and direct ion activity determination of sample solutions. Together with a suitable ion meter or titrator, ISEs form a well affordable and versatile measuring system. ISEs follow the Nernst equation which is familiar to almost any lab. Hence, ISEs are easily understood and in many cases simply applied.

Ion-selective electrodes are used to determine the activity of the ion under consideration (analyte ion). The ion has to be dissolved preferably in water. When the sample does not dissolve, the ion can also be extracted. Otherwise, color and turbidity of a sample do not disturb the measurement. Alternative analytical techniques are ion chromatography (IC) or titration. For IC, the sample solution has to be clear; the analyte ion concentration lies preferably in the ppm range only; and the equipment costs are higher.

ISEs work under conventional laboratory conditions. The typical measuring range extends from 10^-1 to 10^-6 mol/L. The temperature ranges from 0°C to 50 or 80°C depending on the type of ISE. Prevailing values are 20, 25 and 37°C. The admissible pH range is moderate and avoids high alkaline or extreme acidic samples.

These generous conditions open ISE applications in a wide area. Chemical and pharmaceutical samples as well as environmental monitoring, water quality tests, food, and plants are well suited for ISE analysis. ISEs are particularly applied for biological and medical samples because they measure the ion activity.

Find more info in the additional sub-chapters of the Ion Selective Electrode – Theory and Practice Guide

1.1 When are ion-selective electrodes used

1.2 How ion-selective electrodes work

1.3 Selectivity, ionic strength

1.4 Type of ion-selective electrodes

1.5 Typical measuring range

1.6 Electrode response

1.7 Limitations

1.8 Measurement procedures

1.9 Advantages of the measurement procedures

1.10 Low-level calibration technique

Ion-selective electrodes are being used in a wide range of applications. Measurement purposes include research projects, education tasks, production monitoring and quality control. Find below a selection of typical applications in selected industrial segments.

Find more info in the additional sub-chapters of the Ion Selective Electrode – Theory and Practice Guide

2.1 Typical applications in selected industrial segments

2.2 Selected application examples

Reliable and fast ion concentration determinations base on the appropriate measuring system. Five steps lead to the right system for your applications. Let's start with the selection of the right ion meter.

Users of ion meters have different needs and requirements to cover. Hence, manufacturers offer several meters to match. Rather simple meters provide limited functionalities for basic applications. High performance meters come with a lot of functionalities including incremental procedures, built-in methods with automatic result calculations, compliance support and automation. Another criterion is the place of use: A benchtop meter is used in the laboratories. For field use a portable meter is recommended.

METTLER TOLEDO offers a wide range of ion-selective sensors: the perfectION™ line. These combined sensors guarantee top performance as well as easy handling. Thanks to the Click & Clear™ reference junction the sample type hardly matters: whether the ion species of interest is being determined in an easy aqueous solution or in more complex matrices like waste-water, perfectION™ will always give the right results. We provide valuable guidebooks for the following perfectION™ sensors:

• Calcium electrode (51710842)
• Chloride electrode (51710843)
• Cupric electrode (51710844)
• Cyanide electrode (51710845)
• Fluoride electrode (51710846)
• Iodide electrode (51710847)
• Lead electrode (51710848)
• Nitrate electrode (51710849)
• Potassium electrode (51710850)
• Silver/Sulfide electrode (51710851)

Learn more about the combined ion selective electrodes: www.mt.com/perfectION

Find more info in the additional sub-chapters of the Ion Selective Electrode – Theory and Practice Guide

3.1 Select the ion meter

3.2 Choose the sensor

3.3 Choose the solution

3.4 Add ideal further accessories

3.5 Easy system check

This chapter presents some hints and recommendations for the daily use of ISEs. They are based on generally accepted handling and operational rules and support you to reach good practice level. The first sub-chapter emphasizes on sample preparation for ISE measurement.

ISE measurements are carried out in liquid samples. Hence, solid samples need to be dissolved. The analyte ion can often be extracted. Use deionized water for dissolution and extraction. Samples may also need dilution to reach the linear range of the ISE. Dilution solvent: deionized water.

Find more info in the additional sub-chapters of the Ion Selective Electrode – Theory and Practice Guide

4.1 Sample preparation for ISE measurement

4.2 ISE preparatory steps

4.3 Measurement and calibration – stirring and rinsing

4.4 Practical consequences of ISE types

4.5 Storage of ISEs

Good Electrochemistry Practice™ - Know the Risks of Your pH Measurement

Measuring pH in the laboratory is a common analysis, but so many things can go wrong. The same goes for conductivity, ion concentration, dissolved oxygen and redox. Good Electrochemistry Practice™ is about guiding you through the whole product lifecycle, detecting possible risks and finding the right tools to address these and ascertain good results.

• Preservation of the accuracy and precision of results
• Compliance with regulations
• Minimization of risks
• Increased productivity and reduced costs
• Protection of investment

Learn more about Good Electrochemistry Practice

When problems occur follow a systematic procedure to locate the sources of error. Stringently check the four components of the measuring system one by one. Refer to manufacturer data.

The easy system check as explained in a previous chapter is the initial step to locate the problem and restore the original level of performance. A general ion-selective measurement troubleshooting checklist is offered in this guide and includes the following points: meter, electrode, application, technique.