Determination of non-ionic surfactants with esters groups by high-performance liquid chromatography with post-column derivatization

Abstract

A high-performance liquid chromatographic (HPLC) method with a post-column reaction detector was developed for the determination of non-ionic surfactants with esters groups (NSEG) such as sorbitan fatty acid esters and sucrose fatty acid esters. NSEG from the mono- to pentaester are separated by reversed-phase HPLC with gradient elution. NSEG eluted from a chromatographic column are hydrolysed with potassium hydroxide, and the resulting fatty acids are reacted with 2-nitrophenylhydrazine in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide to form 2-nitrophenylhydrazides. The reaction mixture is then made strongly alkaline in order to reduce the blank absorbance and develop a violet colour of the hydrazide, which is detected at 550 nm. The post-column reaction detector, for example, can detect 1 μg of monomyristin. With the proposed method, NSEG are well separated and determined with high sensitivity and selectivity.