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  3. Maintenance & Troubleshooting

Why do my pH readings keep drifting?

When readings keep climbing or bouncing, there is a solution.

Even after waiting a minute or two, sometimes your pH readings can continue to move around. Slowly moving pH readings that move between 0.01 and 0.1 pH units over the course of 30-60 seconds is normal. This can be due to homogenization of the sample, temperature fluctuations, and stirring speed.

What if it's more than that?

The first steps here are CLEANING and MAINTENANCE.

The sensing glass on the the pH electrode may be contaminated. Regular cleaning is recommended to prevent this. However, you should never wipe your electrode to remove residue. This can, and will, strip the pH sensing glass on the bulb. Not only does this strip the electrode of hydration, but it can cause physical damage to glass and cause your readings to become even more erratic. Simply rinse the electrode with deionized water, or for a more in-depth cleaning, use an application-specific cleaning solution. For a detailed list of cleaning solutions visit hannainst.com/cleaning, and for directions on how to properly use each cleaning solution download our pH Electrode Maintenance Guide.
If your readings are still drifiting after your regular cleaning, you may have a clogged junction. To clean a clogged junction, follow the cleaning directions found in our pH Electrode Maintenance Guide. To avoid clogged junctions, remember to rinse your electrode with deionized water between readings, and don't allow your electrode to sit in your sample for long periods of time. Another way to avoid a clogged junction is to have an application specific electrode. For example, if you are working with a viscous food sample, you would want an electrode with an open junction such as our FC200. This will help minimize the chances of the junction getting clogged.
When was the last time you let your electrode soak in storage solution? Last night? The day before? Never? That may be the problem. Water, deionized water, sample, and pH buffers (other than pH 4) all wick away the moisture from the pH sensing bulb and junction, and ions from the electrolyte. Storage solution helps to keep your probe hydrated and happy. If you are working with a harsh sample (i.e. extremely low or high pH samples), we recommend letting your electrode sit in storage solution in-between sample testing to refresh the hydrated layer.


Next, check the SLOPE of the electrode.

To check the slope of a pH electrode, you will need at least 2 pH buffers (preferably 3). For a quick calibration overview please visit our pH Meter Calibration and Electrode Maintenance Guide or for more in-depth information, take a look at our pH Electrode Troubleshooting Guide. One key point here is to check that the buffer hasn't expired.


Is that all set? Take a look at your sample.

1. Is your sample something like purified water? Then you may have a sample with low conductivity. When paired with the improper electrode junction, low conductivity in a sample can cause slow response and drift in pH readings. To remedy this, choose an electrode with a higher electrolyte flow rate, such as our HI10530 triple ceramic junction electrode.
2. Electrical noise interference isn't something we necessarily think about every day. Just like the hum of office chatter can distract you from working, the same goes for your electrode. Noise from stirrers, motors, circuitry, and rectifiers can interfere with your measurements. In this case, you need to either take a "grab sample" and measure the sample away from the vat or use an amplified electrode, or an electrode with a matching pin to reduce interference from electrical noise.


Last but not least, how old is your electrode?

Everything tends to slow down as it ages, and an electrode is no different. The glass isn't as sensitive, the junction may have been clogged one too many times, and the wiring may be starting to wear after being plugged and unplugged numerous times. Even if all maintenance practices are adhered to, an electrode will deteriorate due to every day use, and the harshness of the sample matrix. By performing frequent slope and offset checks, you will be able to determine if the electrode is still okay to use. A slope between 85% and 105%, and an offset of ±30 mV is considered to be in working condition. Anything outside of that range, the electrode should be replaced. All Hanna electrodes are warrantied for 6 months after point of purchase. However, it is not uncommon for pH electrodes used in general (non-specialty) samples to last for 1 - 2 years.


Remember, CLEAN regularly, CALIBRATE often, CONDITION always.