Cited by 243Mass Spectrometry Techniques and ApplicationsElectrohydrodynamics and Fluid DynamicsAdvanced Proteomics Techniques and Applications

Addressing a Common Misconception: Ammonium Acetate as Neutral pH “Buffer” for Native Electrospray Mass Spectrometry

Konermann, Lars·2017·Journal of the American Society for Mass Spectrometry

Abstract

Native ESI-MS involves the transfer of intact proteins and biomolecular complexes from solution into the gas phase. One potential pitfall is the occurrence of pH-induced changes that can affect the analyte while it is still surrounded by solvent. Most native ESI-MS studies employ neutral aqueous ammonium acetate solutions. It is a widely perpetuated misconception that ammonium acetate buffers the analyte solution at neutral pH. By definition, a buffer consists of a weak acid and its conjugate weak base. The buffering range covers the weak acid pK a ± 1 pH unit. NH 4 + and CH 3 -COO - are not a conjugate acid/base pair, which means that they do not constitute a buffer at pH 7. Dissolution of ammonium acetate salt in water results in pH 7, but this pH is highly labile. Ammonium acetate does provide buffering around pH 4.75 (the pK a of acetic acid) and around pH 9.25 (the pK a of ammonium). This implies that neutral ammonium acetate solutions electrosprayed in positive ion mode will likely undergo acidification down to pH 4.75 ± 1 in the ESI plume. Ammonium acetate nonetheless remains a useful additive for native ESI-MS. It is a volatile electrolyte that can mimic the solvation properties experienced by proteins under physiological conditions. Also, a drop from pH 7 to around pH 4.75 is less dramatic than the acidification that would take place in pure water. It is hoped that the habit of referring to pH 7 solutions as ammonium acetate "buffer" will disappear from the literatur…

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Crossref · 10.1007/s13361-017-1739-3

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  • In the presence of ammonium acetate, the pH may drop to values as low as 4.75 ± 1 in the final ESI droplets, reflecting the pKa of acetate buffer.

    “In the presence of ammonium acetate, the pH may drop to values as low as 4.75 ± 1 in the final ESI droplets, reflecting the pKa of acetate buffer50.”
  • CZE separation has frequently been used to analyze glycosylated peptides and glycans, and CZE via TDMS has been used for glycosylation characterization.

    “CZE separation has frequently been used to analyze glycosylated peptides and glycans49,57,80,81 and CZE separation via TDMS was used for glycosylation characterization82.”
  • Ammonium acetate does not form a buffer system that can effectively maintain macromolecular complexes in solution at physiological pH.

    “Since ammonium acetate does not constitute a buffer system that can effectively maintain macromolecular complexes in solution at physiological pH conditions81,100”

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Authors
Konermann, L.
Affiliations
Western University (CA)
Corresponding author
Konermann, Lars
Venue
Journal of the American Society for Mass Spectrometry
Published
2017-07-14
Volume
28
Issue
9
Pages
1827-1835
ISSN
1044-0305 (ISSN-L)
OpenAlex
W2735371049
Cited by
243
References
96
Citations by year
2026: 22 · 2025: 26 · 2024: 39 · 2023: 30 · 2022: 28 · 2021: 28 · 2020: 33 · 2019: 27 · 2018: 9 · 2017: 1
FWCI
9.46
Type
journal article
Language
en
Open access
closed
Locations
  • Journal of the American Society for Mass Spectrometry (publishedVersion)
  • PubMed (publishedVersion)
  • Scholarship@Western (Western University) (submittedVersion)
Funders
Natural Sciences and Engineering Research Council of Canada
Topics
  • Physical Sciences › Chemistry › Spectroscopy › Mass Spectrometry Techniques and Applications
  • Physical Sciences › Engineering › Electrical and Electronic Engineering › Electrohydrodynamics and Fluid Dynamics
  • Physical Sciences › Chemistry › Spectroscopy › Advanced Proteomics Techniques and Applications
Keywords
ammonium acetate, pH buffering, conjugate acid-base pairs, pKa, protein solvation, positive ion mode

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