Multiple‐Injection Method in High‐Temperature Two‐Dimensional Liquid Chromatography (2D HT‐LC)

Comprehensively characterizing the relationship between the distributions with regard to chemical composition (CCD) and molar mass (MMD) of polyolefins is vital to establish structure-property relationships. Two-dimensional high-temperature liquid chromatography (2D HT-LC), which couples a high-temperature solvent gradient interactive chromatography (HT-SGIC) step for compositional separation with a high-temperature size exclusion chromatography (HT-SEC) step for MMD determination in an on-line manner is emerging as a tool of choice to satisfy this necessity. A serious problem commonly associated with multidimensional chromatography is the very low detector response (DR) due to the dilution in the HT-SEC step. Using higher sample concentrations or larger sample loops cannot address this appropriately because injections may become irreproducible, or poorly shaped peaks may result due to concentration effects. This paper shows that stacked injections (repeatedly injecting a polymer sample and then starting the desorption step) is a unique way to overcome these difficulties. 2D HT-LC analysis of blends of ethylene/1-octene copolymers using stacked injections proves that the DR can be significantly enhanced without co-elution of the blend components or overloading of the column.