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ph_measurement_tips [25/06/2019 06:17] pieter |
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===== FAQ ===== | ===== FAQ ===== | ||
//**How often do I need to calibrate my pH meter? | //**How often do I need to calibrate my pH meter? | ||
- | This depends on the type of products being measured, the maintenance and the required accuracy. It may be weekly, daily or before each use or set of uses.\\ | + | This depends on the type of products being measured, the maintenance and the required accuracy. It may be weekly, daily or before each use or set of uses. See [[http:// |
\\ | \\ | ||
//**If measuring the entire range of pH what buffers should be used?**//\\ | //**If measuring the entire range of pH what buffers should be used?**//\\ | ||
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//**What pH electrode do I use for a specific application? | //**What pH electrode do I use for a specific application? | ||
Follow the general rules below for selecting the right pH electrode: | Follow the general rules below for selecting the right pH electrode: | ||
- | * Check the [[http:// | + | |
* Glass bodied pH electrodes may be used in most sample types. | * Glass bodied pH electrodes may be used in most sample types. | ||
* Epoxy bodied pH electrodes are designed for rugged environments, | * Epoxy bodied pH electrodes are designed for rugged environments, | ||
* For situations containing proteins, sulphide, and TRIS, use double junction electrodes. | * For situations containing proteins, sulphide, and TRIS, use double junction electrodes. | ||
* For viscous or dirty samples, use sleeve junction electrodes for best results and easy cleaning. | * For viscous or dirty samples, use sleeve junction electrodes for best results and easy cleaning. | ||
- | \\ | + | * Check the [[http:// |
//**What filling solution do I use?**//\\ | //**What filling solution do I use?**//\\ | ||
The recommended filling solution depends on the type of electrode. Some electrodes have sealed references and do not require filling solution. For refillable pH electrodes, use a 3...4 M KCl solution.\\ | The recommended filling solution depends on the type of electrode. Some electrodes have sealed references and do not require filling solution. For refillable pH electrodes, use a 3...4 M KCl solution.\\ | ||
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* The electrode mV in a pH 4 buffer (at 25°C) should be 160 to 180 mV more than the value in pH 7. | * The electrode mV in a pH 4 buffer (at 25°C) should be 160 to 180 mV more than the value in pH 7. | ||
* The electrode mV in a pH 10 buffer (at 25°C) should be 160 to 180 mV less than the value in pH 7. | * The electrode mV in a pH 10 buffer (at 25°C) should be 160 to 180 mV less than the value in pH 7. | ||
- | * If the mV values are outside of the above ranges, clean the pH electrode. If cleaning does not return the mV to an acceptable range, replace the electrode. Note: as long as the pH electrode has a slope between 92% and 102%, the electrode should be working properly. The pH buffers should be replaced if the measured mV values are outside of the acceptable ranges. Contaminated buffers may slightly contribute to shifted mV values. | + | * If the mV values are outside of the above ranges, clean the pH electrode. If cleaning does not return the mV to an acceptable range, replace the electrode. Note: as long as the pH electrode has a slope between 92% and 102%, the electrode should be working properly. The pH buffers should be replaced if the measured mV values are outside of the acceptable ranges. Contaminated buffers may slightly contribute to shifted mV values.\\ |
- | \\ | + | |
//**My pH electrode is drifting. What should I do?**//\\ | //**My pH electrode is drifting. What should I do?**//\\ | ||
There are three possible causes for electrode drift: | There are three possible causes for electrode drift: | ||
* If the electrode is new (or has been dry) and drifting, the electrode may not be properly conditioned. Refer to the appropriate electrode instruction manual for details. | * If the electrode is new (or has been dry) and drifting, the electrode may not be properly conditioned. Refer to the appropriate electrode instruction manual for details. | ||
* If the electrode is stable in buffers but not in the sample, the electrode may be incompatible with the sample or application. | * If the electrode is stable in buffers but not in the sample, the electrode may be incompatible with the sample or application. | ||
- | * If the electrode is drifting in buffers and samples, the electrode may require cleaning. | + | * If the electrode is drifting in buffers and samples, the electrode may require cleaning, see [[http:// |
* Electrode that have been stored for longer periods may have an air bubble in the pH sensitive glass bulb. To remove it, take the electrode in the hand with the glass buble pointed downwards and shake it like a clinical mercury thermometer until the bubble has vanished. | * Electrode that have been stored for longer periods may have an air bubble in the pH sensitive glass bulb. To remove it, take the electrode in the hand with the glass buble pointed downwards and shake it like a clinical mercury thermometer until the bubble has vanished. | ||