Measurement Limit
Analytical deviation in glass electrodes occurs when measuring highly acidic solutions below a certain pH threshold. This phenomenon, known as acid error, causes the electrode to register a pH value that is higher than the actual value of the bath. The discrepancy becomes pronounced in strongly acidic dye liquors used for wool or nylon processing.
Chemical Cause
High concentrations of hydrogen ions alter the activity of water molecules at the glass bulb surface. This change reduces the hydronium activity in the gel layer, producing an artificial inflation of the measured pH. Such behavior is typical in concentrated acid baths where acid error degrades the precision of measurements.
Testing Boundary
Calibration standards for highly acidic textile processing must account for this phenomenon to prevent dye exhaustion failures. It is observed in environments where pH levels drop below one. Normal calibration procedures using standard buffers cannot resolve the deviation.
Process Consequence
Wet processing operations suffer from uneven dye take up when the true acidity of the liquor is underestimated. If the actual pH is lower than the displayed value, the dye exhausts too rapidly onto the fibre, leading to unlevelness across the fabric roll. Accurate control of the dye rate requires secondary verification by titration.
