Why is it so critical that the Intellical™ PHC101 in particular be stored properly?

Document ID

Document ID TE8042

Published Date

Published Date 07/26/2018
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Question
Why is it so critical that the Intellical™ PHC101 in particular be stored properly?
Summary
Importance of correct PHC101 storage
Answer
This probe has an open junction, which is an important feature that make it both the best option for waste water applications, and extremely sensitive to issues with storage. The open junctions are the two small pin holes on the sides of the probe. This is best for waste water because the suspended solids in that sample matrix will clog the pores of other junction types. Probes with open junctions can't be refillable because the filling solution would simply pour out of the holes. Refillable probes would need to have a porous junction to regulate and limit the flow of electrolyte solution. Which is why this probe has a non-replaceable gel electrolyte.
 
This open junction makes the probe best suited for dirtier sample types, but it also makes the probe very sensitive to storage issues. This is because there is no barrier between the internal electrolyte and the solution the probe is submerged in.
 
Submerging the probe in a sample for longer than what is required to take a reading (for example like in between samples or overnight) causes two problems.  First, the probe with its open junction when it is submerged in anything other than storage solution will continue to lose electrolyte. Essentially it puts the probe in constant use even when measurements are not being taken. Second, submerging the probe for longer than necessary in a sample will often lead to bacterial contamination of the electrolyte in the probe. Most bacteria will make acids as byproducts of their digestion, the increase of acid in the electrolyte will cause offset issues.
 
If the probe is stored in reverse osmosis (RO) or deionized (DI) water in between samples or overnight, this also leads to problems. Like above, it causes a continuous loss of electrolyte. However, this will also introduce an additional problem. When the probe is submerged in DI water this will leach additional ions out of the electrolyte gel through diffusion. This causes the concentration of electrolyte inside the gel to decrease. This difference in concentration between the gel electrolyte and the internal reference solution also causes an offset.

If the probe is submerged in pH buffer in between samples or overnight, this also leads to problems. Again a continuous loss of electrolyte, but as with the bacterial contamination, the pH buffer will leach into the probe and cause the pH of the electrolyte gel to change as well, once again causing an offset issue.

If the probe is submerged in any other storage solution other than Hach pH Electrode Storage Solution (Product # 2756549) it's possible that this could cause problems as well. This isn't necessarily the case with all other storage solutions, but if the storage solution has a different concentration of KCl, contains other ions, or contains stabilizers, these can also alter the internal gel electrolyte and cause offset issues. For example, USA BlueBook storage solution contains KHP as a stabilizer, which will ruin Hach pH electrodes.

Because this probe has a non-replaceable electrolyte if a probe has an offset issue due to any reason, there is no other option then replacement of the probe.
 
Because of these reasons it is crucial with this probe more than any other that the probe be stored in the correct storage solution when not in use. Not just overnight, but in between samples as well. If it is too inconvenient to put on and remove the soaker bottle in between samples, then it would be recommended keep the probe in a beaker of storage solution in between samples.
 
If through troubleshooting it is identified the probe has failed because of improper storage a warranty replacement will be declined since this is not a manufacturing defect and it will be recommend that the probe be replaced. Alternatively, the probe could be replaced with a refillable option which would be the Intellical™ PHC735 Laboratory Dirty Media RedRod Refillable Glass pH Electrode (Catalog Number/Order Code PHC73501). This probe is refillable and is suitable for dirtier samples because it has a high flow annular ring junction which has a larger surface area and larger pores than a standard porous pin junction.

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