3 tips for improving accuracy and repeatability when measuring the Acid Number of petroleum products

Acid Number (AN) is a standard measure of acidity in crude oils and oil products, serving as a crucial indicator of quality and safety of use. AN is determined by the amount of potassium hydroxide required to neutralize acids present in one gram of oil. KEM’s  AT-710 series titrators are perfect for measuring AN, complying with standards such as ASTM D664 and ASTM D3242. In this article, we would like to introduce 3 tips to improve the accuracy and repeatability of AN measurements.

First up, reduce the time between sample preparation and measurement to minimize CO2 from the air dissolving into the solvent. If you are not covering your samples, we suggest setting up an additional burette that adds solvent just before measurement. If you are experiencing poor repeatability or failing to attain a clear inflection point, we recommend purging the beaker's headspace with nitrogen during measurement. Our next tip is to perform electrode restoration. Working with organic solvents causes electrodes to lose sensitivity unless restored (ideally after each measurement). This involves rinsing off sample with solvent, rinsing with pure water to dissolve precipitates at the sleeve, soaking in pure water to restore its aqueous gel layer (soaking time varies between methods), and finally rinsing again with solvent. When wiping off solvent with cleaning tissue, avoid generating static by applying light pressure and a gentle motion. Our last tip regards sample stirring speed. We recommend using a constant speed when measuring, vigorous enough to achieve proper agitation for measurement, but gentle enough to prevent sample spattering and the introduction of air into sample this promotes. If using our titrators, we recommend Stir Speed 2.