One-Step Method for Separation and Identification of n-Alkanes/Oligomers in HDPE Using High-Temperature High-Performance Liquid Chromatography

Abstract

n-Alkanes are often an important ingredient of waxes, oils, gasoline, and a byproduct in polyolefins. Separation and identification of alkanes in commercial high-density polyethylene (HDPE) are of vital importance from various points of view. Currently used chromatographic techniques require extraction and laborious preconcentration. Porous graphite Hypercarb as a stationary phase in high-performance liquid chromatography (HPLC) in combination with a mobile phase gradient n-decane → 1,2-dichlorobenzene (ODCB) enables a selective separation of C40–C160 n-alkanes at temperatures between 100 and 160 °C. Thus, it is possible to resolve the individual alkanes in HDPE of 1 kg/mol. An unambiguous assignment of the individual homologues in the chromatogram was possible by doping the HDPE with a C60 standard, and the results were also confirmed by MALDI TOF. Using this method, the presence of alkanes in a HDPE sample with a weight-average molar mass of 70 kg/mol could be shown. n-Hexane as isocratic mobile phase e...