Total acid number

• Potentiometric titration: The sample is normally dissolved in toluene and propanol with a little water and titrated with alcoholic potassium hydroxide. A glass electrode and reference electrode is immersed in the sample and connected to a voltmeter/potentiometer. The meter reading is plotted against the volume of titrant. The end point is taken at the distinct inflection of the resulting titration curve corresponding to the basic buffer solution.
• Color indicating titration: An appropriate pH color indicator e.g. phenolphthalein, is used. Titrant is added to the sample by means of a burette. The volume of titrant used to cause a permanent color change in the sample is recorded and used to calculate the TAN value.
• Spectroscopic methods: as with many chemical parameters, spectroscopy can be used to make fast, accurate measurements once calibrated by a reference method. Mid and near infrared spectroscopy are most commonly used for this purpose. Spectroscopic methods are valuable as they can also be used to simultaneously measure a number of other parameters and do away with the need for wet chemistry.