If you are a customer of ZP and have our solid state pH sensors here is a quick start guide to calibrating them:

STEP ONE - Insert the sensor into the electrical connection and apply 50 µL of calibration solution 1 (pH 10). Make sure to properly cover the electrodes. Start the measurement and wait 60 seconds for stabilization. Record the average of the last 10 seconds as the first calibration point.

STEP TWO - Stop/pause the measurement and remove the sensor. Clean the electrode gently using DI-water. Insert the sensor back into the device and apply 50 µL of calibration solution 2 (pH 4). Make sure to properly cover the electrodes. Start/resume the measurement and wait 60 seconds for stabilization. Record the average of the last 10 seconds as the second calibration point. Stop/pause the measurement and remove the sensor. Clean the electrode gently using DI-water.

STEP THREE - Create a linear fit using the two calibration points acquired obtained in STEPS ONE and TWO.

STEP FOUR - Insert the sensor back into the device and apply 50 µL of the sample solution. Make sure to properly cover the electrodes. Start/resume the measurement and wait 60 seconds for stabilization. Record the average of the last 10 seconds as the second calibration point. The linear fit acquired in STEP THREE will translate the millivolt signal to a pH value.

The same procedure can also be performed with submersion of the sensor instead of drop testing. 

Note that the more the calibration solution resembles the actual sample, the more accurate the result will be. For very complex sample matrices, it might be necessary to make up the calibration solution in the actual sample matrix.