Uncertainty of Routine pH Measurements Evaluated by the Principle of Pooled Calibrations

In the digital age, taking logarithms of data is no longer necessary
when assessing pH measurement uncertainties. The focus is now on
using raw, unaltered data. Routine pH measurements often differ
from those in reference labs, so quantifying these differences is
necessary. The uncertainties of pH values at 25°C were evaluated
using mass-by-mass calculations, along with comparisons between
two pH meters. Four buffer systems and several beverage samples
were tested. Expanded uncertainties (U) of up to U = 0.36 were
observed for pH values between 2 and 11, significantly higher than
those reported by manufacturers. While measured pH values were
slightly higher than calculated ones, overlapping confidence
intervals allowed the data to be combined. Due to significant
uncertainties, the reliable pH range was limited to 1 < pH < 11,
potentially narrower (1 < pH < 6.5). Routine pH measurement
uncertainties did not match those based on the PoPC, with notably
high CV values for proton activities at pH values below the buffers'
pKa.