Automated determination of acid value on fatty alcohols and fatty acids raw materials using potentiometric titration

Abstract

The acid value (AV) is a common parameter in the specification of fats and oils (Ph.Eur. 2.5.1, current ed.). It is defined as the weight of potassium hydroxide (KOH) in mg needed to neutralize the organic acids present in 1 g of fat and it is a measure of the free fatty acids (FFA) in a sample of oil or fat indicates hydrolysis of triglycerides. Such reaction occurs by the action of lipase enzyme and it is and indicator of inadequate processing and storage conditions (i.e. high temperature and relative humidity). Different fat samples may contain varying amount of fatty acids. In addition, the fats often become rancid during storage and this rancidity is caused by chemical and enzymatic hydrolysis of fats into free acids and glycerol. The amount of free acids present, or acid value of fat is a useful parameter which gives an indication about the age and extent of its deterioration. The amount of free fatty acids can be determined by volumetric titration (manual), by which a sample in mixture of equal volumes of ethanol (96 per cent) and light petroleum is neutralized with potassium hydroxide (KOH) or sodium hydroxide (NaOH) using phenolphthalein indicator. (Ph.Eur. 2.5.1, current ed.). This is the recommended pharmacopeial procedure in many countries. But this manual method is attended with problems such as indicator error, the unclear color change in the transition range of the indicator may be a source of error. Тhe volumetric titration has a lower rank of precision and accuracy due to this visual problem. To avoid the problem described, this method was optimized by automated titration using potentiometer. In the following we will discuss the automatic determination of the acid value of two raw materials and the comparison of results with the same method volumetric vs potentiometric. Potentiometric titration