Alkaline Measurement
Measurements of pH in highly basic solutions are subject to an instrumental distortion that occurs when the glass electrode begins to respond to sodium ions instead of hydrogen ions. This effect, known as sodium ion error, causes the meter to display a pH value that is lower than the actual alkalinity of the solution. This distortion represents a challenge when monitoring mercerization baths or scouring solutions that contain high levels of caustic soda.
Chemical Substitution
Standard glass membranes are designed to be selective to hydrogen ions, but at high pH, the concentration of hydrogen ions is extremely low. When sodium ions are present in high concentrations, they can penetrate the gel layer of the glass bulb and generate an electrical potential. This potential mimics the signal of hydrogen ions, leading to a falsely low pH reading.
Production Influence
Dye houses can experience incorrect chemical dosage during mercerization if the sensor is suffering from this alkaline error. The technician might add more sodium hydroxide to the bath because the meter indicates the pH is below the required level, leading to waste and potential fabric damage. This issue can cause variations in the fabric’s affinity for dyes.
Technical Resolution
Specialized glass formulations that incorporate lithium instead of sodium are used to minimize this error in highly alkaline environments. These electrodes are less sensitive to sodium ions, providing more accurate measurements at pH levels above twelve. Utilizing these specialized probes ensures closer control of concentrated alkali processes.
