Products for USB Sensing and Control
Products for USB Sensing and Control

How To Keep pH/ORP Sensors Accurate

Or How we Learned this Through Shipping many Ph-Orp electrodes

by Everett

Given the manhandling that goes on in many mail distribution centres, how exactly should one ship a delicate sensor like a pH/ORP electrode, ensuring it stays moist, doesn’t freeze, and doesn’t bump around as to avoid putting the sensor bulb in direct contact with anything. And what about these dried out bulbs? Is it game over for the sensor? Not necessarily. Here’s what we learned through the many trials of shipping pH/ORP electrodes.

In order to keep the bulb moist, we originally shipped a storage solution in a special cap that enclosed the bulb. Shipping is an abusive process though, and despite the rubber gasket that sealed this cap, the solution still leaked out. Eventually, we discovered that it is not necessarily a death sentence for the electrode if the bulb dries out, provided the bulb is allowed to rehydrate for a sufficient time after. It turns out, it’s far easier to ship the storage solution in a separate bottle within the same package.

In the end, shipping the electrode and the solution separately like this was the right way to go. Not all couriers want to carry liquids, especially when they’re interacting with such a strange looking instrument as an electrode. Luckily, the other issues with leaking and drying out came before any interrogations ensued.

It wasn’t immediately obvious that allowing the probes to dry out would work. With some of our rehydrated probes on hand, we began to test. We picked up some lab samples for testing, which had certified calibrations written on the bottle. No matter what we did, our probes would not return accurate results. Luckily, one thing worked, and that was time. When you get a dried out pH or ORP electrode, immerse it in the solution for at least 48 hours before using. Voila. It is best to keep the probe stored in the solution at all times. This will allow you to forgo the lengthy rehydration process when you wish to take measurements and extend the life of the probe.

The storage solution is a pH electrode storage solution available at scientific instrument shops. We used the WD-00653 from Oakton (a mix of H2O, KCl, Na2HPO4 and KH2PO4)

That’s not the end of the challenges with shipping pH/ORP electrodes though. Being situated in Canada, we contend with Canadian winters, which introduces the risk of the electrode freezing while in transit. If the electrode does freeze, the odds are that it will be destroyed. Keeping the electrode from freezing in winter is simply a matter of minimizing the exposure to sub zero temperatures. Express shipping offers the answer in this regard because the package will spend most of its time within an airplane or a warehouse. Ground shipping on the other hand usually involves un-insulated and un-heated trailers that are prone to sit at sorting facilities while they wait to be processed.

With the lessons learned, Phidgets now ships pH/ORP electrodes without issues. All the customer has to do is soak the electrode in the storage solution (sent with the electrode) for a couple of days and the sensor will perform accurate readings for a long time to come.

If you’ve been using pH or ORP probes for anything, let us know what you’re doing and how it’s working.