ASTM D664-04 pdf free.Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration.
Titrate in this manner until the potential changes lessthan 5 mV/0.1 mL of KOH and the cell potential indicates thatthe solution is more basic than the aqueous basic buffer. Remove the titration solution，rinse the electrodesand burette tip with the titration solvent, then with propan-2-oland finally with reagent grade water. Immerse the electrodes inwater for at least 5 min before starting another titration torestore the aqueous gel layer of the glass electrode.After 5 minin the water，rinse the electrodes with propan-2-ol then thetitration solvent before proceeding to the next titration. If theelectrodes are found to be dirty and contaminated, proceed asin 8.1.Store electrodes according to 8.3.3.
Automatic Titration Method:Adjust the apparatus in accordance with the manu-facturer’s instructions to provide a dynamic mode of titrantaddition.Verify that the instrument will determine the amountof strong acid when the initial mV of the test sample, relativeto the mV reading of the aqueous acidic buffer，indicates thepresence of such acids. Record the volume of KOH added toreach the mV of the pH 4 aqueous buffer. This value is used tocalculate the strong acid number. Proceed with the automatictitration and record potentiometric curves or derivative curvesas the case may be.Titrate with the 0.1-mol/L alcoholic KOH solution.The apparatus shall be adjusted or programmed such that,when an inflection point, suitable for use in the calculation isapproached, the rate of addition of titrant and volume of titrantadded are based on the change in slope of the titration curve.The titrant shall be added in increments of a suitable size toachieve a potential difference of 5 to 15 mV per increment.Increment volume shall vary between 0.05 and 0.5 mL.Thenext increment shall be added if the signal does not changemore than 10 mV in 10 seconds. The maximum waiting time inbetween increments shall not exceed 60 seconds. When strong acids are present and a strong acidnumber is to be determined, perform a blank titration of 125mL of the titration solvent,adding 0.1 mol/L alcoholic HClsolution in 0.01 to 0.05-mL increments in a manner compa-rable to that specified in 11.5.1.ASTM D664 pdf download.