ASTM D1121 method for Reserve Alkalinity of Engine Coolants and Antirusts
9. Preparation of Electrode System
9.1 Maintenance of Electrodes - Clean the glass electrodes at frequent intervals (not less than once every week during continual use) in accordance with the manufacturer's instructions. Drain the calomel electrodes at least once each week and fill with KCl electrolyte. Keep the electrolyte level in the calomel electrode above that of the liquid in the titration beaker at all times. When not in use, immerse the lower half of the electrodes in water and do not allow them to be immersed in the titrated solution for any appreciable period of time between titrations. Although the electrodes are not extremely fragile, they should be handled carefully at all times.
9.2 Preparation of Electrodes - Before and after using, blot the glass electrode thoroughly with a clean cloth, or a soft, absorbent tissue, and rinse with water. Blot the calomel reference electrode with a cloth or tissue; carefully remove the ground-glass sleeve and thoroughly blot both ground-glass surfaces. Replace the sleeve loosely and allow a few drops of electrolyte to drain through to flush the ground-glass joint. Wet the ground surfaces thoroughly with electrolyte, set the sleeve firmly in place, and rinse the electrode with water. Prior to each titration, soak the prepared electrode in water for at least 2 min. Immediately before use, touch the tips of the electrodes with a dry cloth or tissue to remove excess water.
10. Electrode System in pH Units
10.1 Turn on the instrument, allow to warm up, and adjust in accordance with the manufacturer's instructions. Allow sufficient time for the temperature of the buffer solution and immersed electrodes to equalize and set the temperature knob at the temperature of the buffer solution. Calibrate the assembly with a minimum of two buffer solutions to check the linearity of the response of the electrode or incorrect temperature compensation. The presence of a faulty electrode is indicated by a failure to obtain a reasonably correct value for pH of the second standard solution when the meter has been standardized with the first. A cracked electrode will often yield pH values that are essentially the same for both standards. Adjust the standardization or asymmetry potential control until the reading of the dial corresponds to the known pH of the standardizing buffer solution.
