ARTICLE IN PRESS JID: CHROMA [m5G;January 13, 2020;13:17] Journal of Chromatography A xxx (xxxx) xxx Contents lists available at ScienceDirect Journal of Chromatography A journal homepage: www.elsevier.com/locate/chroma Retention of polypropylene stereoisomers in solvent gradient interaction chromatography on porous graphitic carbon as influenced by temperature and mobile phase composition Anthony Ndiripo, Harald Pasch ∗ Department of Chemistry and Polymer Science, University of Stellenbosch, Stellenbosch, 7602 South Africa a r t i c l e i n f o Article history: Received 26 September 2019 Revised 23 December 2019 Accepted 8 January 2020 Available online xxx Keywords: Polypropylene Tacticity Atomic level flat surface Porous graphitic carbon Solvent gradient interaction chromatography a b s t r a c t The behavior of isotactic, syndiotactic and atactic polypropylene stereoisomers on porous graphitic carbon (PGC) at different column temperatures is investigated with 1-decanol, decalin and decane as the adsorp- tion promoting solvents using gradient interaction chromatography (SGIC). Column temperatures between 120 – 180 °C are investigated for the three adsorption promoting solvents with 1,2,4-trichlorobenzene (TCB) as the desorption promoting solvent. Owing to the different stereochemistry of the isomers, their interaction with the atomic level flat surface (ALFS) of porous graphitic carbon is observed to be different when injected from the three different adsorption promoting solvents. Atactic and isotactic polypropylene are not separable when 1-decanol is used as the adsorption solvent but can be separated from syndio- tactic PP at column temperatures of between 120 – 180 °C. The three stereoisomers have almost similar elution volumes when decalin is used as the adsorption promoting solvent between 120 – 170 °C. De- cane allows for both adsorption and desorption of the stereoisomers at distinct peak elution volumes at the studied column temperatures of 120 – 160 °C. Furthermore, it is shown that increasing the col- umn temperature while maintaining other chromatographic conditions can either decrease or increase retention depending on the adsorption promoting solvent. More importantly, retention is influenced by adsorption conditions (temperature and adsorption promoting solvent) which may affect macromolecular conformations upon injection onto the PGC stationary phase. This is the first study on PP stereoisomers highlighting this behaviour. © 2020 Elsevier B.V. All rights reserved. 1. Introduction Method development for the comprehensive analysis of the molecular composition of complex polyolefins is an important topic for both academia and industry. Over the last 50 years, sen- sitive and robust methods have been developed for the analy- sis of polyolefins with regard to molar mass, molecular topology, chemical composition and microstructure [1–5]. For the chemical composition analysis, spectroscopic methods such as Fourier trans- form infrared (FTIR) and nuclear magnetic resonance (NMR) spec- troscopy are in place; information on the chemical composition distribution (CCD) can be obtained by crystallization-based frac- tionation methods such as temperature rising elution fractionation (TREF), crystallization analysis fractionation (CRYSTAF) or crystal- lization elution fractionation CEF [6–9]. ∗ Corresponding Author. E-mail address: hpasch@sun.ac.za (H. Pasch). Chromatographic methods that separate polyolefins regarding chemical composition, branching or microstructure irrespective of crystallizability, have been introduced only 15 years ago. High tem- perature solvent gradient interaction chromatography (HT-SGIC) operates at temperature conditions above the melting and crys- tallization temperatures of the polyolefins and enable chemical composition separations that are based on selective adsorptive in- teractions between the analyte and the chromatographic station- ary phase [1,2,10–13]. Recently, a complementary interaction chro- matography mode termed high-temperature temperature gradient interaction chromatography (HT-TGIC) has been introduced. Here, an isocratic thermodynamically good solvent is used as the mobile phase while a temperature gradient is applied for the fractionation process. The most common stationary phase for such separations is porous graphitic carbon (PGC) that exhibits an atomic level flat surface (ALFS). [14–16] As the first results of interaction chromatography of polyolefins appeared only from 2003 onwards [1,2,10], much remains to be understood with regard to the mechanisms of separation and the https://doi.org/10.1016/j.chroma.2020.460865 0021-9673/© 2020 Elsevier B.V. All rights reserved. Please cite this article as: A. Ndiripo and H. Pasch, Retention of polypropylene stereoisomers in solvent gradient interaction chro- matography on porous graphitic carbon as influenced by temperature and mobile phase composition, Journal of Chromatography A, https://doi.org/10.1016/j.chroma.2020.460865