Understanding mobile phase buffer composition and chemical structure effects on electrospray ionization mass
Allison Brookhart1, Mahika Arora2, Michael McCullagh3
1Department of Biochemistry and Molecular Biology, University of Massachusetts Amherst, MA.
Journal of Chromatography. A
|April 13, 2023
Summary
Selecting mobile phases for liquid chromatography-mass spectrometry (LC-MS) is crucial. Chemical structure, not mobile phase composition, primarily dictates electrospray ionization (ESI) response for small molecules.
Area of Science:
- Analytical Chemistry
- Biochemistry
- Pharmacology
Background:
- Mobile phase selection critically impacts liquid chromatography-mass spectrometry (LC-MS) performance, influencing retention, selectivity, ionization, and detection limits.
- Generalized criteria for mobile phase selection in LC-MS across diverse chemical compounds are currently lacking.
- Electrospray ionization (ESI) is a widely used ionization technique in LC-MS, but its efficiency can be analyte-dependent.
Purpose of the Study:
- To conduct a large-scale assessment of mobile phase composition effects on electrospray ionization (ESI) response.
- To evaluate ESI response for 240 small molecular weight drugs across various chemical classes using reversed-phase LC.
- To identify key factors influencing ESI response in LC-MS analyses.
Main Methods:
- Reversed-phase liquid chromatography coupled with mass spectrometry (LC-MS) was employed.
- A diverse set of 240 small molecular weight drugs were analyzed.
- Qualitative assessment of mobile phase composition and its effect on ESI response was performed.
Main Results:
- Chemical structure, particularly surface area and charge, was the dominant factor influencing ESI response (approx. 85% of variance).
- Mobile phase composition showed less differentiation in ESI response, though pH effects were noted for some compounds.
- Isopropanol-based solvents and those with phosphoric or di-/trifluoroacetic acids performed poorly; methanol/acetonitrile with formic acid/ammonium acetate showed best generic performance.
Conclusions:
- Analyte's intrinsic chemical structure is the primary determinant of ESI response in LC-MS.
- While mobile phase composition is secondary, optimal generic solvent systems involve methanol or acetonitrile with formic acid and ammonium acetate.
- Further research into structure-specific mobile phase optimization may be warranted for challenging analytes.
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