Supercritical Fluid Nanospray Mass Spectrometry: II. Effects on Ionization

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Supercritical Fluid Technology

Background:

• Traditional liquid eluents in mass spectrometry face limitations in desolvation efficiency.
• Nanospraying supercritical CO2 (nSF-MS) offers improved desolvation and high sensitivity detection.
• Understanding analyte properties and emitter size effects is crucial for optimizing nSF-MS.

Purpose of the Study:

• To evaluate the impact of proton affinity, hydrophobicity, and nanoemitter tip size on nSF-MS signal intensity.
• To investigate the performance of nSF-MS using various amine classes and alkyl chain lengths.
• To determine the optimal conditions for nSF-MS in complex biological matrix analysis.

Main Methods:

• Utilized a nanospraying supercritical fluid coupled to a mass spectrometer (nSF-MS) system with a 90% supercritical CO2 carrier.
• Analyzed sets of primary, secondary, tertiary, and quaternary amines with varying alkyl chain lengths (butyl, hexyl, octyl, decyl).
• Employed nanoemitter tips with internal diameters of 25, 50, and 75 μm.

Main Results:

• Hydrophobicity demonstrated a greater influence on signal response than proton affinity.
• A linear dynamic range of 0.1-100 μM was achieved, indicating mass-sensitive detection.
• Larger emitters (75 and 50 μm) showed increased signal with hydrophobicity, while the 25 μm emitter exhibited a decrease.
• Quaternary amines showed no signal suppression in mixtures, unlike primary, secondary, and tertiary amines.

Conclusions:

• The nSF-MS system with 90% sCO2, methanol, and formic acid provides fast desolvation, high ionization efficiency, and minimal matrix effects.
• Hydrophobicity is a key factor influencing signal intensity in nSF-MS, with emitter size playing a critical role.
• The observed signal behavior in the 25 μm emitter suggests novel ionization mechanisms in sub-500 nm nanospraying, beneficial for complex sample analysis.