Theoretical and practical guidelines for solvent dilution between the two dimensions in online comprehensive...

Area of Science:

• Analytical Chemistry
• Chromatography

Background:

• Online comprehensive two-dimensional liquid chromatography (LC x LC) is increasingly utilized.
• Combining hydrophilic interaction chromatography (HILIC) and reversed-phase liquid chromatography (RPLC) offers high orthogonality but faces solvent incompatibility challenges.
• Dilution of the first dimension effluent is a common strategy to mitigate solvent mismatch in LC x LC systems.

Purpose of the Study:

• To develop theoretical models for predicting the effectiveness of effluent dilution in online LC x LC.
• To determine the minimum dilution factor (z_dilution) required for acceptable peak shapes.
• To guide the selection of optimal HILIC x RPLC conditions based on compound characteristics.

Main Methods:

• Calculation of the ratio (x_dilution) between injection-induced peak standard deviation and baseline peak standard deviation.
• Plotting x_dilution as a function of z_dilution to predict required dilution.
• Experimental validation using small molecules and peptides in HILIC x RPLC systems.

Main Results:

• Theoretical models were developed to predict dilution effectiveness in online LC x LC.
• A maximum x_dilution value of approximately 1 was found to be necessary for acceptable peak shapes.
• Experimental results showed high agreement with theoretical predictions, particularly for small molecules.

Conclusions:

• The developed theoretical approach accurately predicts the required dilution factor for effective peak shape in online LC x LC.
• This method aids in optimizing HILIC x RPLC conditions for specific analytes.
• The findings facilitate the practical implementation of online LC x LC for complex separations.