How to calibrate your pH electrode 

Glad it was helpful!

@@MetrohmTV Is it still advisable to use pH 9 buffer for calibration bracketing samples with expected higher pH values, even though alkaline buffers have a high CO2 uptake?

For precise pH measurement results, we always recommend a multi-point calibration. The pH of the sample should always be within the pH range of the buffers that are used for calibration to minimize errors. So, if you are expecting higher pH values (e.g., pH 8) the use of pH buffer 9 is advisable. To avoid a carbon dioxide uptake of buffers with higher pH values, always use fresh buffer solutions. Our buffer solutions in single use sachets are quite suitable for this. If you have more questions on pH measurement and calibration please have a look at our current monograph “pH-measurement - everything from A-Z including best practices and examples”: www.metrohm.com/en/products/8/1085/81085081.html

You're welcome!

Thanks!

Hi gidissadeksissa2219 Do you mean the initial concentration of an analyte? The initial concentration of an analyte is not affected if the analyte is sodium, hydroxide, hydronium, or chloride. Does this answer your question, or did we misunderstand it? Best regards Metrohm International Headquarters

Thank you 🙂

Hi Thank you for your comment. Could you please check if another electrode can be calibrated? This way we would know if the problem lies with the instrument or the sensor. In general, if you require instrument support, please contact your local Metrohm organization or exclusive distributor. BR Michel, Metrohm International Headquarters

We would recommend calibrating the sensor daily and at the temperature of the samples for exact results. It depends a bit on the accuracy that is required.

Hi This very much depends on the accuracy of the result you want to achieve. For example, if the result is only a rough guide, it is fine to perform a calibration or replace the electrolyte before the pH measurement. However, if you want the result to be as accurate as possible, maintenance is more important and should be carried out at least monthly or even weekly. In general, frequent maintenance of the electrode is recommended for warranty reasons and also with regard to the lifetime of an electrode.

@@MetrohmTV Thanks a lot for your answer !

@@BenoitPlomb-u8l You're welcome. We hope this helps!

Hi Samuel Thank you for your comment. You always have to calibrate with buffers which lie within your measuring range. With buffers pH 4, 7, and 9, you’re already covering quite a broad pH range. Should you need to cover an even broader range, you can use pH buffers from other manufacturers. As for the electrode: The electrode has to be dipped in in such a way that the diaphragm is fully covered by your measuring solution. I.e., the glass membrane and diaphragm have to be immersed but the electrolyte filling hole has to stay above the sample. Best regards Michel, Metrohm International Headquarters

@@MetrohmTV 😀 thanks for your reply 😊

Hi Erick There could be various reasons for this. You can find additional information on this topic in our Application Bulletin AB-188: www.metrohm.com/en/applications/ab-application-bulletins/ab-188.html If you need to troubleshoot your instrument or sensor, please get in touch with your local Metrohm subsidiary or exclusive distributor: www.metrohm.com/en.html#country-selection BR Michel, Metrohm International Headquarters

Hi Thank you for your comment. Typically, a buffer measurement should not take more than a few seconds or a few minutes at most. A measuring time of 45 minutes is a clear indicator that something is not right, the most obvious candidate being a defective electrode. Please check whether your electrode needs to be replaced or contact your local Metrohm organization if you need technical support: www.metrohm.com/en.html#country-selection Best regards Metrohm International Headquarters

Since temperature has an impact on your pH measurement (Nernst equation), calibration and pH measurement should be performed at the same temperature, e.g., at 25 °C. For further information please read our blog post “How temperature influences the pH value”: www.metrohm.com/en/discover/blog/2023/how-temperature-influences-the-ph-value.html

Hi Buffer sachets are for single use only. Metrohm buffers in the bottle last up to 3 months after opening and are easy to store on shelves. After a calibration, the buffer should be discarded and should not be reused. You can find more information in this blog post: www.metrohm.com/en/discover/blog/20-21/faq--all-about-ph-calibration.html

The electrode slope is given by the Nernst equation and is 0.059 V per pH 1 at 25 °C. These are ideal values from which new Metrohm pH electrodes only differ slightly. The electrode zero point is ± 0.015 V. But please be aware that the electrode zero point and the electrode slope may change as a result of the aging of the glass membrane or changes (e.g., contamination) on the diaphragm. For more information on this topic, please read our blog “FAQ: All about pH calibration”: www.metrohm.com/en/discover/blog/20-21/faq--all-about-ph-calibration.html And our our application bulletin AB-188 “pH measurement technique”: www.metrohm.com/en/applications/ab-application-bulletins/ab-188.html

That's exactly the right way to do it!😊