Welcome to ZP's page on calibrating ion-selective electrodes, if you have found this page we would always recommend contacting us as we are in a constant cycle of product improvement.
At Zimmer and Peacock we are pushing towards the most accurate and precise sensors in our users hands, which will come from a combination of good science. manufacturing, characterization and testing.
One of the questions we are ask ourselves and we are asked by our client base is how reusable are our sensors and do they need re-calibration between use. Eventually we want to be able to say that our sensors don't require calibration and that they are stable when in use and between use.
As we walk the road towards entirely calibration free and 100 % stable ISE including: pH, sodium, potassium. calcium, ammonium, chloride we are making discoveries and improvements. Here we show the data from two potassium ISE tested on two consecutive days. Our conclusion is that the sensors are re-usable and that the sensitivity is stable, but the off-set is variable. So at the time of writing this note we woudl suggest a one-point calibration, but as said elsewhere in this document feel free to contact us to find out our most recent findings.
In the adjacent image we have taken two potassium ISE sensors on two different days and tested them with the same three potassium concentrations: 2.7 mM , 4 mM and 6 mM of potassium ions.
What we see is a signal that is proportional to potassium concentration, but what we also see is that on the second days the signal shows a similar slope/gradients/sensitivity but all the signal have changed their absolute values, which we describe as a baseline shift. The simplest 'fix' for this would be to perform a single point calibration with a known potassium concentration and adjust/compensate for this.