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Sample Preparation for Probe Electrospray Ionization Mass Spectrometry
Published on: February 19, 2020
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Negative ion formation in electrospray mass spectrometry.
1Analytical and Chemical Sciences, Research Triangle Institute, P.O. Box 12194, 27709-2194, Research Triangle Park, NC, USA.
Journal of the American Society for Mass Spectrometry
|November 15, 2013
Summary
Negative ion electrospray ionization (ESI) on a single quadrupole mass spectrometer effectively detects low-molecular-weight compounds. This method provides complementary structural data for unknown compounds, particularly nucleotides and explosives, with high sensitivity.
Area of Science:
- Analytical and Chemical Sciences
- Mass Spectrometry
- Ionization Techniques
Background:
- Electrospray ionization (ESI) is a common technique for analyzing various molecules.
- Negative ion mode ESI (NI-ESI) offers potential for complementary structural information.
- Optimization of NI-ESI parameters is crucial for sensitive detection of low-molecular-weight compounds.
Purpose of the Study:
- To discuss the application of negative ion electrospray (ES) on a single quadrupole mass spectrometer for detecting low-molecular-weight molecules.
- To compare negative ion mode ES with the conventional positive ion mode.
- To identify optimal conditions for NI-ESI, including solvent choice and pH, for enhanced sensitivity and structural elucidation.
Main Methods:
- Operated the ES interface at a positive cylindrical electrode potential to generate negative ions.
- Compared results from negative ion mode with positive ion mode operation.
- Evaluated various chromatographic solvents and gas additives (e.g., 2-propanol with oxygen) for optimal performance.
- Investigated the effect of capillary voltage and solvent pH on ion formation and fragmentation.
Main Results:
- Negative ion ES successfully produced ions with solvation and fragmentation patterns from diverse solutes including antibiotics, nucleotides, peptides, and explosives.
- Optimal conditions for NI-ESI involved using 2-propanol with oxygen in the ES bath gas to suppress discharge and enhance ion transfer.
- Increased solvent pH significantly improved sensitivity in negative ion ES ionization.
- Detection limits down to 1 pg/mL were achieved for nucleotides and explosives in negative ion mode.
Conclusions:
- Negative ion ES on a single quadrupole mass spectrometer is a valuable technique for analyzing low-molecular-weight compounds.
- NI-ESI provides complementary structural information, aiding in the characterization of unknown compounds.
- The method is particularly effective for analyzing nucleotides and explosives, offering high sensitivity and structural insights.
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