Optimization of experimental parameters for separation of nonionic surfactants by supercritical fluid chromatography

Abstract

A synthetic polymer generally consists of a mixture of many compounds that share the same repeating unit but have different degrees of polymerization. Because of its ability to cope with a wide range of molecular weights, supercritical fluid chromatography (SFC) is a powerful technique for separating the individual components of polymers. However, the separation conditions for SFC are more sensitive than those of other types of chromatography, and many experimental parameters need to be carefully selected to achieve high resolutions. Methods for optimizing the experimental parameters for SFC of a polymeric surfactant were investigated by chemometric techniques. Increases or decreases in peak resolution and elution times were measured for the separation by SFC of the nonionic surfactant poly(ethylene glycol) nonylphenyl ether for various column temperatures, flow-rate gradients of modifier, and modifier compositions. To maximize the separation efficiency, the experimental results were analyzed by using the chromatographic response function (CRF). This is a function of the desired peak resolution, the maximum acceptable elution time, and an arbitrary weighting factor that is adjusted to achieve an optimal balance between the peak separation and the elution time. Because the numerical value of the CRF changes in response to the chromatographic performance, it provides a means of identifying the conditions for achieving optimal separation for a particular SFC system.