ANALYSIS OF SORBITAN ESTER SURFACTANTS .2. CAPILLARY SUPERCRITICAL-FLUID CHROMATOGRAPHY

A rapid, simple and quantitative approach to the separation and identi fication of sorbitan ester surfactants has been developed using capill ary supercritical fluid chromatography (SFC). The sorbitan ester surfa ctants were well separated into five groups: starting materials and mo no-, di-, tri-, and tetraesters, with each group consisting of a numbe r of peaks representing different isomers. High purity glycerides of f atty acids were employed to estimate the relative response factors of sorbitan esters, and reliable group-wise integration served for quanti tation of the distribution of sorbitan fatty acid esters. A very impor tant parameter, hydrophilic-lipophilic balance (HLB), which describes the hydrophilic and hydrophobic characteristics of surfactants, could be correlated with the distribution of the sorbitan esters. A combinat ion of solid-phase extraction (SPE) and SFC was used to separate, conc entrate, and analyze Span-20 from salt-water samples. In comparison wi th the HPLC method, capillary SFC broadens the scope of the technique to encompass high molecular weight sorbitan polyesters while maintaini ng high separation efficiency.