Potentiometric titration of long chain tertiary amine oxides and tertiary amines using a poly(vinyl chloride) membrane electrode

Abstract

Two separate potentiometric titrations are used to quantify mixtures of long chain tertiary amine oxide and tertiary amine as their cations. A direct titration of the mixture in water at pH 2 against a standard sodium lauryl sulfate solution, using a poly(vinyl chloride) membrane sensing electrode, determines the total surfactant content, reported as % m/m tertiary amine oxide. A simple extraction is used to separate the tertiary amine, which is subsequently titrated under the same conditions. This titration is quantitative for dimethylalkylamine oxides and their corresponding amines (where alkyl = C₁₀–C₁₆). Seven analyses are performed on an aqueous mixture and give the following results: tertiary amine oxide, 23.8 ± 0.1% m/m and tertiary amine, 1.0 ± 0.1% m/m, at a 95% confidence level. This method is capable of determining tertiary amine at 0.1% m/m in the presence of 25% m/m tertiary amine oxide with no interference. The same aqueous mixture is spiked with tertiary amine to test the quantitative recovery of the amine. The recovery is 3.1% m/m compared with an expected value of 3.2% m/m amine.