March 2026
By Lina Herrera Cortes1, Olivier Boyron1, Alberto Ortín2, Nuria Mayo2, Manel TAAM1
1CP2M, Équipe Polymérisation, Catalyse et Matériaux UMR 5128, CNRS-Université Lyon 1, 43, boulevard du 11 Novembre 1918 BP.2077 69616 Villeurbanne Cedex
2Polymer Characterization, S.A. Gustave EiSel 8, Paterna, Valencia Technology Park E-46980 Spain
Complementary Insights from IR and DRI Detection in HT-SEC
Introduction
Combining differential refractive index (DRI) and infrared (IR) detection in high-temperature size-exclusion chromatography (HT-SEC) enables simultaneous monitoring of molecular weight and chemical composition. For some polymer solvent combinations the IR detector provides accurate concentration and molar mass information, while dRI can be used when there is no IR absorption or with solvents which are not IR-compatible. In addition, the IR detection identifies functional groups and compositional variations in polymers such as EVA, EBR, PE, PP, and PS. This complementary approach reveals details like comonomer distribution, oxidation, or additive content along the chromatographic profile, offering a more complete characterization of polymers for quality control, material development, and recycling studies.
Instrumentation
IR6: Advance Infrared Detection for HT-SEC
The IR6 is Polymer Char’s most advanced IR detector, offering high sensitivity and stability. It detects absorption from CH bonds (methyl and methylene groups in the band 2,800 – 3,000 cm-1) and carbonyl groups (1,740 cm⁻¹), enabling precise analysis of EVA, EBA, and functional polyolefins even at low concentrations.
Its superior signal-to-noise ratio allows detailed compositional and branching analysis.
Prototype Refractometer
In collaboration with Polymer Char, the CP2M laboratory evaluated a unique prototype refractometer designed to improve sensitivity, linearity, and thermal stability compared with conventional DRI detectors. The goal was to validate its performance and to compare it directly with the IR6 detector across a range of polymers and concentrations.
Experimental Conditions
- Equipment: GPC-IR® (Polymer Char)
- Column oven temperature: 160 °C
- Detector block temperature: 150 °C
- Columns: 3 × PL-GEL Olexis + guard (pre-column)
- Run time: 35 min
- Flow rate marker (for alignment): heptane, 1.5 % v/v
- Filtration: 0.045 μm (samples/solvent)
Results and Discussion
Chromatogram of an EVA polymer in IR6 and dRI
1. Comparison between IR6 and DRI Detectors
IR6 and DRI chromatograms of an EVA sample show nearly identical molar mass distributions, confirming that both detectors provide consistent measurements.
Key Observations:
- Comparable separation: IR6 and DRI deliver similar molar mass distributions.
- Chemical selectivity: Unlike DRI, IR6 detects specific functional groups (C=O, CH3).
- Enhanced analysis: IR reveals compositional drift and chemical heterogeneity along the molar mass distribution.
- Comprehensive insight: IR6 provides both quantitative and qualitative information.
2. Influence of concentration on DRI and IR6 detector response
Calibration System Constants- Mass constant: 0.40 mL·V·mg⁻¹ (as configured)
- Inter-detector volume (conc → viscometer): 0.852 mL
- Viscometer constant (dv): 0.0943
The performance of DRI and IR6 was evaluated at low (~3 mg/8 mL) and high (~16 mg/8 mL) sample concentrations.
Results:
- At low concentration, the DRI shows limited sensitivity and reduced signal-to-noise ratio, while the IR6 remains highly sensitive.
- At high concentration, both detectors show improved correlation and approach ideal agreement.
Conclusion:
The IR6 demonstrates superior robustness and stability over a wide concentration range.
3. Comparison of Molar Mass Determination by DRI and IR6 for various Polymers
PVB, PE, PS, and EVA
- Analyzed at identical concentrations.
- Molar masses were calculated using both conventional and universal calibration approaches.
- Mw values obtained from IR6 and DRI show strong agreement for all polymers.
IR6 yields molar mass results that are comparable to DRI on all the samples, validating its use as a concentration detector while adding chemical selectivity.
Ethylene–butadiene rubber (EBR)
EBR materials are widely used in tire formulations due to their balance of elasticity, abrasion resistance, and low-temperature flexibility.
Polythiophene and derivatives – Universal vs Conventional
Conducting polymers such as polythiophene are lightweight, flexible, and chemically tunable materials used in electronics and optoelectronics (OLEDs, organic LEDs), energy storage, sensors, and biomedical applications. These polymers are capable of conducting electricity due to their conjugated π- electron systems along the backbone.
The molar masses (Mn and Mw) calculated using conventional and universal calibrations show very similar values between the IR and DRI detectors, confirming that both detectors provide consistent results even for advanced functional materials.
