A novel sample preparation for chloride analysis in bar soaps

A simple and rapid sample preparation technique is described for the potentiometric determination of chloride in bar soaps. Usual preparation of soap for potentiometric chloride analysis involves time-consuming dissolution of the sample in water or heating to affect dissolution, followed by a cooling step. Also, when performing potentiometric titrations for chloride under the usual acid conditions, aqueous solutions of soap bars (unlike combination soap/detergent bars) will form insoluble semisolid fatty acids that can occlude some chloride and make clean-up difficult. This paper describes a simple dissolution of bar soap sample in dilute H₂SO₄/methanol at ambient temperature that simultaneously acidifies the sample solution and produces noninterfering methyl esters from the soap fatty acids; water is then added, and the chloride is determined potentiometrically with standardized AgNO₃. This procedure has been shown to work well with automatic titrators.