Boosting GPC/SEC data reproducibility and accuracy with a flow marker

Importance of the Topic

GPC/SEC is key for characterizing polymers and biomolecules by molecular weight. However, small flow rate fluctuations can shift retention times or elution volumes, compromising calibration accuracy and reproducibility. Incorporating a flow marker (FM) peak within each chromatogram offers a stable internal reference that enables correction of these variations, thereby enhancing the reliability of molar mass determinations.

Objectives and Overview of the Study

• Assess the impact of flow rate fluctuations on GPC/SEC calibration and molecular weight results.
• Evaluate the effectiveness of an FM-based correction approach across a series of controlled experiments.
• Demonstrate practical benefits of FM implementation for routine polymer analysis workflows.

Methodology and Instrumentation

The study utilized three aqueous GPC/SEC experiments with ethylene glycol as the FM. Key steps included:

• Sample and standard preparation: Pullulan standards (180–1 450 000 Da) and glucose oligomers were dissolved in water; ethylene glycol (1.5 mg/ml) served as the FM.
• Instrumentation: AZURA P 6.1L pump, AZURA AS 6.1L autosampler, AZURA RID 2.1L refractive index detector, AZURA CT 2.1 thermostat, AppliChrom SuperOH column; controlled by ClarityChrom® software with GPC extension.
• Correction workflow: The FM peak retention time was marked, triggering flow rate correction in the calibration and sample evaluation routines via defined correction factors.

Key Results and Discussion

• Experiment A (Calibration curves): Simulated 20% flow rate increase yielded a 5th-order calibration with R²=0.9995 after FM correction versus R²=0.8918 without. Deviations from the corrected curve remained within ±7% compared to >100% errors otherwise.
• Experiment B (Accuracy tests): A standard mix measured at 0.8, 1.0, and 1.2 ml/min showed that FM-based corrections reduced retention time deviations to below 5% across all flow rates.
• Experiment C (Sample measurements): Sugars analyzed at an elevated flow rate (1.2 ml/min) displayed significant molar mass overestimation without FM correction. Applying FM adjustments limited mass deviations to under 10%, restoring accurate molecular weight assignments.

Benefits and Practical Applications

• Improved reproducibility and accuracy of GPC/SEC measurements despite pump instabilities.
• Seamless integration into existing data processing workflows via software correction features.
• Broad applicability for aqueous and organic separations by selecting compatible flow markers.

Future Trends and Potential Applications

Advancements may include automated selection and dosing of FMs, integration with real-time system diagnostics, and expansion to multi-detector setups. Novel marker compounds tailored to specific chemistries can enable more robust applications in biopharmaceuticals, materials science, and quality control environments.

Conclusion

The inclusion of an internal flow marker in GPC/SEC analyses provides a straightforward and effective strategy to correct flow rate fluctuations, yielding highly reproducible calibration data and accurate molar mass determinations. Proper marker selection—ensuring solubility, narrow distribution, and non-overlapping elution—is essential for optimal results.

Reference

• KNAUER Wissenschaftliche Geräte GmbH application note Boosting GPC/SEC data reproducibility and accuracy with a flow marker (2025).