Study on the separation mechanism of solid-substrate electrospray ionization mass spectrometry

Area of Science:

• Analytical Chemistry
• Separation Science

Background:

• Solid-substrate electrospray ionization mass spectrometry (SSEIMS) is a key ambient ionization technique simplifying mass spectrometry.
• While its separation applications are growing, the underlying separation mechanism remains unclear, with chromatography proposed as a factor.

Purpose of the Study:

• To elucidate the separation mechanism in substrate-filled capillary SSEIMS.
• To investigate the roles of chromatographic and electric field effects in SSEIMS separations.

Main Methods:

• Utilized over thirty small molecules (neutral, basic, weakly acidic) as model compounds.
• Employed C18-bonded silica gel and silica gel as substrates within a capillary.
• Validated chromatographic effects via oil-water distribution coefficients and electric field effects using t-tests on retention times at varying voltages (5.5 kV vs. 4.0 kV).
• Proposed a differential equation to quantify compound retention under an electric field.

Main Results:

• Chromatographic effects were confirmed through the oil-water distribution coefficient.
• Electric field effects were statistically significant (p < 0.01) in influencing retention times.
• A quantitative method was developed and validated for analyzing proline and hydroxyproline in plasma with high accuracy and selectivity.
• Demonstrated rapid quantification of proline (31.88 μg/mL) and hydroxyproline (20.71 μg/mL) in plasma samples.

Conclusions:

• The separation mechanism in SSEIMS is a synergistic combination of chromatographic and electric field effects.
• This understanding provides theoretical guidance for optimizing SSEIMS separation.
• The findings will advance SSEIMS applications in biological, pharmaceutical, forensic, food, and environmental analyses.