Secondary ion emission from solutions: time dependence and surface phenomena

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Surface Science

Background:

• Fast Atom Bombardment (FAB) mass spectrometry is a crucial technique for analyzing non-volatile and thermally labile compounds.
• Understanding the temporal dynamics of ion emission in FAB is essential for accurate quantitative analysis.
• Surfactants like tetradecyltrimethylammonium bromide (TTAB) and tetraethylammonium iodide (TEAI) are common in various applications and require precise characterization.

Purpose of the Study:

• To investigate the temporal behavior of FAB mass spectra for TTAB and TEAI in glycerol solutions.
• To correlate FAB spectral data with secondary ion imaging to understand ion emission mechanisms.
• To elucidate the role of surface tension and matrix evaporation in FAB analysis of these surfactants.

Main Methods:

• FAB mass spectrometry was employed to analyze glycerol solutions of TTAB and TEAI over time.
• Secondary ion imaging was used to visualize the spatial distribution of ions on sample droplets.
• Time-resolved spectral analysis and spatial imaging data were correlated.

Main Results:

• FAB spectra of TTAB solutions showed a consistent decrease in tetradecyltrimethylammonium ions (TTA+) over time.
• TEAI solutions initially exhibited stable spectra, followed by an increase and then a sharp decrease in tetraethylammonium ions (TEA+).
• Secondary ion imaging revealed homogeneous ion emission for TTAB but heterogeneous, segregated emission for TEAI, correlating with spectral observations.

Conclusions:

• The observed temporal and spatial differences in ion emission are attributed to surface tension-induced mass transport and glycerol matrix evaporation.
• FAB analysis of TTAB and TEAI in glycerol is significantly influenced by dynamic surface phenomena.
• These findings provide insights into the complex mechanisms governing FAB mass spectrometry, particularly for surfactant solutions.