Accelerating Modifier-Free SFC Separations with the Agilent 1260 Infinity II SFC System

Significance of the topic

The versatility of supercritical fluid chromatography (SFC) extends across a wide polarity range, enabling highly efficient separations of hydrophobic compounds using only CO2. This green methodology reduces organic solvent waste and supports sustainable practices in environmental analysis and industrial quality control.

Study objectives and overview

This technical overview evaluates the performance of the Agilent 1260 Infinity II SFC System for modifier-free separations of a 16-component polycyclic aromatic hydrocarbon (PAH) mixture. The study focuses on improving the peak shape and reducing run times of late-eluting compounds by applying backpressure and flow gradients while preserving early-eluting analyte resolution.

Methodology and instrumentation

An Agilent 1260 Infinity II SFC System was configured with a control module, binary pump, multisampler, multicolumn thermostat and diode array detector. Separations employed an Agilent InfinityLab Poroshell 120 EC-C18 column (3.0 × 150 mm, 2.7 µm). Key parameters included:

• Mobile phase: 100 % CO2 at 40 °C
• Flow rate (isocratic): 2.5 mL/min; injection volume 1 µL in MTBE with feed speed 1000 µL/min and 4 µL overfeed
• Backpressure regulator (BPR): set at 150 bar, held at 60 °C
• Detection: diode array at 223 nm with 360 nm reference, 20 Hz

Main results and discussion

The base isocratic method achieved full separation for 10 of 16 PAHs, with coelution and partial resolution for the remainder. Two gradient strategies were compared:

• Backpressure gradient from 150 to 300 bar over 0.5 minutes (1–1.5 min) reduced runtime by 25 % to 3.63 minutes and improved peak symmetry. Retention time RSDs remained below 0.15 %, and area RSDs below 1 % for most peaks. A moderate decrease in detector response was observed due to density changes of CO2.
• Flow gradient from 2.5 to 4.0 mL/min over 0.5 minutes cut runtime by 37 % to 3.03 minutes and yielded the best peak shape for late eluters. Retention time and area RSDs increased slightly but remained within acceptable limits.

Benefits and practical applications

Modifier-free SFC with CO2 offers a rapid, environmentally friendly approach for analyzing hydrophobic compounds such as PAHs in environmental samples and fuels. The flexibility to apply pressure and flow gradients enhances method versatility for complex mixtures and supports high-throughput workflows.

Future trends and potential applications

Advancements in dynamic pressure and flow control promise further runtime reductions and resolution gains. Integration with mass spectrometry and broader adoption of novel stationary phases will expand the scope of modifier-free SFC in pharmaceuticals, petrochemicals and food analysis. Improved understanding of density and viscosity effects will refine gradient strategies and detector calibration.

Conclusion

The Agilent 1260 Infinity II SFC System enables efficient modifier-free separations using pure CO2. By employing backpressure or flow gradients, late-eluting analytes can be effectively focused, resulting in significantly shortened run times and enhanced peak shapes without compromising early-eluter resolution. This approach underlines SFC as a green, high-performance alternative for routine and research laboratories.

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