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Exploring the mechanism of salt-induced signal suppression in protein electrospray mass spectrometry using experiments and molecular dynamics simulations
- Source :
- Analytical chemistry. 87(4)
- Publication Year :
- 2015
-
Abstract
- Protein analyses by electrospray ionization (ESI) mass spectrometry can suffer from interferences caused by nonvolatile salts. The mechanistic basis of this effect remains to be fully investigated. In the current work we explore the behavior of proteins under native and denaturing conditions in the presence of NaCl, CsCl, and tetrabutyl ammonium chloride (NBu4Cl). All three salts interfere with the formation of "clean" [M + zH](z+) protein ions by progressively deteriorating spectral S/N ratios. We propose that salt interferences can be dissected into two independent aspects, i.e., (i) peak splitting by adduct formation and (ii) protein ion suppression. NaCl degrades the spectral quality by forming heterogeneous [M + zH + n(Na - H) + m(Cl + H)](z+) ions, while the integrated protein ion intensity remains surprisingly robust. Conversely, NBu4Cl does not cause any adduction, while dramatically reducing the protein ion yield. These findings demonstrate that adduct formation and protein ion suppression are indeed unrelated effects that may occur independently of one another. Other salts, such as CsCl, can give rise to a combination of the two scenarios. Molecular dynamics simulations of water droplets charged with either Na(+) or NBu4(+) provide insights into the mechanism underlying the observed effects. Na(+) containing droplets evolve relatively close to the Rayleigh limit (z/z(R) ≈ 0.74), whereas the z/z(R) values of NBu4(+) charged droplets are considerably lower (∼0.59). This difference is due to the high surface affinity of NBu4(+), which facilitates charge ejection from the droplet. We propose that the low z/z(R) values encountered in the presence of NBu4(+) suppress the Rayleigh fission of parent droplets in the ESI plume, thereby reducing the yield of progeny droplets that represent the precursors of gaseous protein ions. In addition, the rate of solvent evaporation is reduced in the presence of NBu4(+). Both of these factors lower the protein signal intensity. NaCl does not interfere with droplet fission, such that protein ions continue to form with high yield—albeit in heavily adducted form. Our findings expand on earlier proposals of charge competition as a key factor during the ESI process for salt-contaminated solutions.
- Subjects :
- Spectrometry, Mass, Electrospray Ionization
Electrospray ionization
Analytical chemistry
Salt (chemistry)
Ion suppression in liquid chromatography–mass spectrometry
Molecular Dynamics Simulation
Sodium Chloride
010402 general chemistry
Mass spectrometry
01 natural sciences
Analytical Chemistry
Ion
Adduct
Molecular dynamics
chemistry.chemical_compound
Animals
Horses
chemistry.chemical_classification
Ubiquitin
010401 analytical chemistry
Egg Proteins
Cytochromes c
Heart
0104 chemical sciences
chemistry
Ammonium chloride
Cattle
Salts
Chickens
Subjects
Details
- ISSN :
- 15206882
- Volume :
- 87
- Issue :
- 4
- Database :
- OpenAIRE
- Journal :
- Analytical chemistry
- Accession number :
- edsair.doi.dedup.....e97cb89496cdf4d23bf6ab03d40d6965