I have a Hanna Instruments pHmeter whose electrode needs to be refilled. However, at the time I'm unable to get the fill solution from HI directly. In the specs of the equipment, it establishes that a 3.5M KCl solution is needed. The vendors that are available for me, offer a 3M KCl solution only.
If I use this solution, will this affect my electrode or measurement?
Thanks in advance for your help.
Hello Alex Patino ,
In my opinion, it should be OK, but you should give the electrode a good amount of time to stabilise and calibrate appropriately.
However, surely an easier option may just be to purchase KCl and make your own 3.5 M solution?
https://www.sigmaaldrich.com/catalog/search?term=7447-40-7&interface=CAS%20No.&N=0&mode=partialmaxfocus=product&lang=fr®ion=FR&focus=product&gclid=EAIaIQobChMIu9yrkpqk4AIVWuh3Ch25hQniEAAYASAAEgIuh_D_BwE
Jules
You can use a 3M KCl solution, but only if it is specified for electrode filling (it is also saturated with Ag+, i.e. AgCl). Don't use a KCl solution prepared by you because it is not Ag+ saturated. The variation of the electrode potential will be -5 mV (compensated by calibration).
See a table for potential values here:
http://www.consultrsr.net/resources/ref/refpotls.htm
It does not matter whether you use 3.0 M or 3.5 M KCl as the reference filling solution as long as (1) you take account of the above comment by Cornel Radu, and (2) you calibrate your pH meter / electrochemical cell with standard pH buffer solutions and then use your pH vs. E (mV) calibration line to obtain the pH of your unknown samples.
Everything else being equal (sample composition, temperature etc.), I would expect an offset of about 4 mV between the old (based on the 3.5 M filling electrolyte) and new (3.0 M) calibration curves since [log(3.5) – log (3.0)] x 59 mV = 4 mV
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