Retention in high-performance liquid chromatography at -196°C.

Area of Science:

• Analytical Chemistry
• Chromatography Science

Background:

• High-performance liquid chromatography (HPLC) typically operates at ambient temperatures.
• Developing HPLC methods for specific applications, such as analyzing volatile compounds, presents unique challenges.

Purpose of the Study:

• To propose and validate a retention model for ultralow-temperature HPLC (ULT-HPLC) at -196°C.
• To elucidate the dominant retention mechanisms based on mobile phase composition in ULT-HPLC.
• To investigate the influence of stationary phase chemistry on analyte retention at cryogenic temperatures.

Main Methods:

• Development of a novel retention model integrating adsorption exchange and "pseudo partition" mechanisms.
• Experimental validation of the model using liquid nitrogen-based mobile phases at -196°C.
• Comparative analysis of analyte retention on bare-silica and octadecylsilyl-modified silica (ODS) columns.

Main Results:

• The proposed retention model demonstrated excellent agreement with experimental data.
• Adsorption exchange and pseudo partition mechanisms were identified as dominant retention modes in low and high additive concentration regions, respectively.
• ODS columns exhibited greater retention for alkanes compared to bare-silica columns.
• Specific analytes, like propylene, were successfully eluted from an ODS column at -196°C with ethane and ethylene additives, unlike on a bare-silica column.

Conclusions:

• The developed retention model provides a robust framework for understanding and predicting analyte behavior in ULT-HPLC.
• Mobile phase composition critically influences retention mechanisms, shifting between adsorption and pseudo partition modes.
• Stationary phase selection significantly impacts chromatographic performance at cryogenic temperatures, enabling the separation of challenging analytes.