What is the procedure for and purpose of adding KCl crystals to the filling solution of a Red Rod electrode?

Document ID

Document ID TE6896

Version

Version 4.0

Status

Status Published

Published Date

Published Date 09/28/2018
Question
What is the procedure for and purpose of adding KCl crystals to the filling solution of a Red Rod electrode?
Summary
Adding KCl crystals to a Red Rod electrode
Answer
Additional salt crystals may need to be added to the filling solution of the probe, This can be done by adding the crystals directly through the fill hole, the easiest way is to mix a small amount of IntelliCAL RED ROD Saturated KCl Refill Solution, 59 mL (Product # 25118026) and KCl Crystals (Radiometer Analytical), 15 g (Product # S21M001) in a small beaker, then use a 15 mL Transfer Pipette (Product # 2750701) to add this through the filling hole of the probe.

It is recommended to have approximately 0.5 cm (0.2 in) of KCl crystals in the filling solution for best results if samples are at or below 60 °C.  Additional KCl crystals can be added as needed if all of the KCl crystals in the filling solution have dissolved. The purpose of the KCl crystals is to maintain saturation, so that if the temperature increases, and therefore the amount of KCl that can be dissolved increases, some of the crystals will be available to be dissolved to maintain saturation. More info here:
Is it normal to receive a Red-Rod electrode with salt in and on the probe? So, this is most important if samples at higher temperatures. If all of KCl crystals become dissolved while the probe is in the sample, that is an indication that more KCl crystals should be added. There is a table in the user manuals for the IntelliCAL™ Red Rod electrodes that gives a recommended KCl crystal ammount for various sample temperatures.

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