How do you calibrate ion selective electrodes?

Like all electrochemistry meters it is vital you calibrate your meter before use to maintain accurate and reliable measurements. As low concentration ISE standards are unstable, the most common method of calibration is to dilute a 1000ppm standard into at least 2, preferably 3 concentrations that bracket your expected sample concentration.  Ideally the standards should be a decade in concentration apart such as 1, 10, 100ppm or 0.01, 0.1 and 1ppm.

Ionic strength adjustment buffers, or ISABs, are used to make sure both the standard and the sample have the same ionic strength so that the concentration, not the activity, is measured by the ISE meter. ISAB must therefore be added to both your sample and each concentration of standard used for calibration. 

ISE calibration method:

• Perform a dilution of your 1000ppm TRUEscience standard for your chosen parameter and add 50ml of each dilution into a labelled, analytically clean, beaker 
• Add iSAB appropriate to ratio – as a guide if the sample concentrations in the 1 to 1000ppm range 1ml of a 2M ISAB to 5-ml sample is satisfactory
• On the TRUEscience app use the calibration tab to start your calibration
• Firstly add your standard dilution group into the app, once you’ve set these up once you can repeat calibration with the same set in the future to save time
• Select start calibration on the app, rinse your electrode with deionised water and place into the lowest concentration standard
• Repeat this step for all the standards making sure you thoroughly rinse your electrode between standards
• You are now ready to measure your sample – take 50ml of your sample and add 1 ml of ISAB
• A stirrer is recommended but not essential to ensure sample homogeneity. The measurement itself should be static.  ​

​For more information on ion selective electrode measurements, calibration or more about the innovative Bluetooth TRUEscience SMART Cap please get in touch with the team on or give us a ring on 01954 233 517.