Determination of Nitrite, Nitrate, and Bromide in Seawater by UV/Vis Detection after Suppression

Significance of the Topic

Pharmaceutical, food, environmental and industrial laboratories often face complex mixtures containing chiral molecules, structural isomers or trace contaminants. Ultra-high performance liquid chromatography (UHPLC) and supercritical fluid chromatography (SFC) each offer distinct retention mechanisms and selectivities. By uniting both modes on a single platform, analysts can accelerate method development, improve resolution, and expand the range of separations accessible without extensive reconfiguration of equipment.

Objectives and Study Overview

This work presents the development and evaluation of the Shimadzu Nexera UC/s UHPLC/SFC switching system. Key aims comprised:

• Assessing the complementary separation selectivity of UHPLC and SFC for isomeric and chiral analytes.
• Demonstrating automated method scouting across multiple chiral columns and mobile phases.
• Validating rapid mode switching and chromatographic reproducibility.

Methodology and Instrumentation

The switching system integrates a standard UHPLC pump, CO2 delivery unit, back-pressure regulator and a multi-port switching valve to share autosampler, column oven and detector between UHPLC and SFC modes. UHPLC uses water-organic mobile phases, while SFC employs supercritical CO2 modified with methanol or ethanol. Automated solvent purging and column equilibration routines enable mode transitions in under ten minutes. Dedicated software orchestrates solvent delivery, valve switching and batch table generation for up to twelve columns.

Used Instrumentation

• Shimadzu Nexera UC/s UHPLC/SFC switching system
• CO2 delivery module and back-pressure regulator (10 MPa)
• Shim-pack HRC-SIL and UC-SIL columns (4.6 mm × 250 mm, 5 µm)
• Chiral columns (CHIRALPAK IA, IB, IC, ID, IE, IF series)
• PDA detector at 220–290 nm
• LabSolutions Method Scouting software

Main Results and Discussion

1. Analysis Speed and Efficiency

• SFC achieved three-to-five-fold shorter runtimes than UHPLC on identical packing, thanks to lower mobile phase viscosity and enhanced diffusivity.

2. Complementary Selectivity

• SFC altered elution order of isomeric tocopherols and pharmaceutical drugs compared to UHPLC, resolving coelutions and improving sensitivity.
• Structural isomers oleanic and ursolic acid, poorly separated by reversed-phase HPLC, were baseline resolved by SFC.

3. Automated Method Scouting

• Thirty-six combinations of six chiral columns and three mobile phase modifiers were screened automatically.
• Multi-Data Report software ranked resolution metrics to identify optimal UHPLC conditions for omeprazole and SFC conditions for warfarin.

4. Reproducibility

• Three analytes (propranolol, indapamide, ibuprofen) were analyzed over multiple switch cycles with negligible retention shifts or carryover.

Benefits and Practical Applications

• Single-platform dual-mode operation reduces footprint, cost and downtime associated with instrument reconfiguration.
• Automated method scouting accelerates chiral and isomer separation development, lowering labor and consumable use.
• Orthogonal selectivity enhances impurity profiling, QA/QC and trace analysis in regulated industries.

Future Trends and Potential Applications

Advances may include integration with mass spectrometry for enhanced sensitivity, expanded solvent control for mixed fluid chromatography, and AI-driven method optimization. Broader column chemistries and high-throughput automation will further streamline complex separations in drug discovery, food safety and environmental monitoring.

Conclusion

The Nexera UC/s switching system effectively combines UHPLC and SFC on one platform, offering orthogonal separation selectivity, rapid analysis and fully automated method development. This dual-mode approach addresses challenging isomeric and chiral separations, improves laboratory efficiency and provides a scalable solution for diverse analytical demands.

Reference

Terada H, Uchikata T, Matsumoto K, Yamaguchi T, Funada Y. Improving Separation and Method Development Efficiency Using the Nexera UC/s UHPLC/SFC Switching System. Shimadzu Application Note C190-E212, December 2018.