oxidation
It is almost impossible to achieve an accurate pH measurement of nearly pure ethylene glycol. pH meters are susceptible to errors and instability when used in organic liquids. A simplistic concept of pH is that of a dimensionless measure of the hydrogen ion concentration in solution. The hydrogen ion comes from dissociation. Since most pure organic materials do not dissociate, pH is not an applicable method. With water in the solution, dissociation does occur and any pH reading is likely some measure of the water and its dissolved materials. The higher the MEG concentration the less accurate the pH measurement. pH papers respond over a 2 pH unit band dependent upon the pKa of the dye used in the paper.
Degradation. Is the MEG un-inhibited? MEG degrades by auto-oxidation in the presence of oxygen. Degradation is accelerated by temperature and metal ions in solution. MEG is oxidized to one of 5 different organic acids. These acids attack certain metals in the system. Minimizing contact with air will minimize degradation. Inhibitors protect metals from attack, retard degradation, and neutralize (buffers) acids formed by degradation. The organic acids are not useable by pH methods for determining the health of the MEG solution. They are weak acids that dissociate very little.
Organic hydrocarbons should not contribute to the degradation of the MEG.
