Hyphenation of Supercritical Fluid Chromatography and NMR with In-Line Sample Concentration

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Chromatography

Background:

• Supercritical fluid chromatography (SFC) coupled with nuclear magnetic resonance (NMR) offers powerful analysis of complex mixtures.
• Dilution of analytes in the supercritical CO2 (scCO2) mobile phase during SFC often leads to concentrations too low for effective NMR detection.
• Excessive signal averaging is typically required to overcome low analyte concentrations, limiting analytical throughput.

Purpose of the Study:

• To develop and demonstrate an in-line sample concentration method for hyphenated SFC-NMR.
• To improve the sensitivity and practicality of SFC-NMR for analyzing complex mixtures.
• To enable direct spectroscopic characterization of microfluidic samples post-SFC separation.

Main Methods:

• A hyphenated SFC-NMR system was designed with an integrated in-line sample concentration unit.
• In-line concentration was achieved by controlled expansion of the supercritical CO2 mobile phase.
• Four isomers of vitamin E (tocopherol) were separated using SFC, concentrated via CO2 expansion from 120 to 50 bar, and analyzed by NMR.

Main Results:

• The integrated in-line concentration method effectively increased analyte concentrations after SFC separation.
• Abundant isomers of vitamin E were readily detected by NMR spectroscopy using the developed setup.
• The system demonstrated the feasibility of microfluidic sample characterization post-SFC.

Conclusions:

• The developed in-line concentration technique significantly enhances the sensitivity of SFC-NMR analysis.
• This approach overcomes the limitations of analyte dilution in scCO2, making SFC-NMR a more viable analytical tool.
• The method supports the direct spectroscopic characterization of microfluidic samples, broadening the applicability of SFC-NMR.