potential measurement (temperature of all samples must be similar!)
Put ca. 50 ml of the comparison sample À back in the PE-cup.
Mix slowly with a PTFE stirrer on the magnetic mixer (remember
speed). Dip both electrodes and note the potential U1 in mV
at the pH-meter. Rinse the electrodes with demineralised water
and measure the potentials in both other samples (first bath
sample: UB, then comparison sample Á: U2) as described.