Strong Acid Anions Significantly Increasing the Charge State of Proteins during Electrospray Ionization

Rationale The performance of mass spectrometry (MS) analysis is often affected by the presence of salt ions. To achieve optimal MS detection results, desalting is necessary for samples with high salt concentrations. We report a rapid, low‐cost and flexible online desalting method using Nafion‐coated sponge. This method is easy to perform and can be implemented to a wide range of customized fluidic systems. Methods Nafion‐coated melamine sponge was fabricated by soaking a glass tube containing a melamine sponge in Nafion solution and then drying overnight. The online desalting workflow is comprised of three major parts: (1) Syringe pump, which provides a continuous flow for the online fluid system; (2) Nafion sponge in a glass tube, where the online desalting of sample solution happens; (3) Capillary Vibrating Sharp‐Edge Spray Ionization (cVSSI), which is an ionization technique to ionize the desalted analytes. Results Effective online desalting of a 10 mM NaCl solution was demonstrated for a wide range of molecules including small molecules, peptides, DNAs, and proteins using a flow rate of 10 μL/min. By incorporating multiple pieces of the Nafion‐coated sponge, effective desalting for ubiquitin and cytochrome c (Cyt‐c) from physiological buffers, including phosphate‐buffered saline (PBS) and tris‐buffered saline (TBS), were also achieved. For molecules that are sensitive to low pH conditions after desalting, a R‐SO3NH4‐type Nafion‐coated sponge was fabricated. Desalting of ubiquitin, oligosaccharide, and DNA oligomers from 10 mM NaCl or 10 mM KCl solutions was demonstrated. Conclusions Flexible, low‐cost, and efficient online desalting was achieved by the Nafion‐coated sponge. A variety of molecules ranging from small molecules, peptides, proteins to oligosaccharides and DNAs can be desalted for MS analysis. The desalting by Nafion sponge has great potential for desalting applications that require customized fluidic design and rapid analysis.

Section: Resultsmentioning

confidence: 99%

Rapid and flexible online desalting using Nafion‐coated melamine sponge for mass spectrometry analysis

DeVor

Wang

et al. 2022

“…To show the excellent sensitivity for OH-PAHs in real biosamples using PR-nESI, we further achieved the detection of Compared with our group's previous works, 21,26,27 PR-nESI was successfully adopted for the sensitive and direct analysis of environmentally exposed bio-samples in negative polarity. To better illustrate the analytical performance of our method, the analytical properties of PR-nESI for detection the OH-PAHs in bio-samples were also comparable with those of other methods that had been previously reported (Table 1).…”

Section: Applications In Biological Samplesmentioning

confidence: 99%

“…In our previous work, a PR-nESI method was developed to improve the performance of nanoelectrospray (nano-ESI) for the sensitive analysis of biomacromolecules and small polar molecules with complex matrices in positive polarity. 21,26,27 In this work, PR-nESI was applied for the highly sensitive and specific analysis of lowpolar OH-PAHs in biological samples with complex matrices. The PR-nESI was first adopted for the analysis of metabolites of PAHs in negative polarity.…”

mentioning

confidence: 99%

Direct analysis of hydroxylated polycyclic aromatic hydrocarbons in biological samples with complex matrices using polarity‐reversed nanoelectrospray ionization

Tan

Wang

et al. 2022

Self Cite

Rationale: Polycyclic aromatic hydrocarbons (PAHs) are a class of environmental contaminants with carcinogenic effect drawing worldwide attention. PAHs can be converted into hydroxylated PAHs (OH-PAHs) through metabolic processes. Thus, they are commonly considered as an important class of biomarkers of PAH exposure.However, direct analysis of related metabolites of these environmental pollutants in biological samples using mass spectrometry is still challenging because of matrix effect and ion suppression during nanoelectrospray ionization (nano-ESI).Methods: In our previous work, a polarity-reversed nanoelectrospray ionization (PR-nESI) technique was developed for the analysis of biomolecules in complex matrices.In this work, we further optimized PR-nESI for direct and sensitive analysis of OH-PAHs in different samples under severe salt interference in negative polarity.Results: Compared with conventional nano-ESI, the optimized PR-nESI method realized sensitive detection of 1-naphthol in samples with a concentration of salt up to millimolar level. The signal-to-noise ratio (S/N) of OH-PAHs was increased by 1À2 orders of magnitude compared with conventional nano-ESI. Six different OH-PAHs were successfully detected with high S/N ratio using PR-nESI. PR-nESI was further successfully applied in the analysis of OH-PAHs in spiked fetal blood serum, human urine, and single-cell samples. For environmentally exposed subjects, the detections of OH-PAHs in single-cell samples and urines from human smokers were successfully conducted. Conclusion:The optimized PR-nESI method was successfully applied for the sensitive analysis of OH-PAHs in complex biological samples with severe salt effects.Based on the present study, PR-nESI can have a promising prospect for the sensitive analysis of other metabolites of environmental pollutants in negative polarity. | INTRODUCTIONPolycyclic aromatic hydrocarbons (PAHs) are a class of persistent organic pollutants (POPs), 1 which enter into the environment through natural sources (natural wildfire, volcanic eruption, extraterrestrial, and organic sediment decay) and human activities (incomplete combustion of fossil fuels, woods, tobacco, and other biofuels). 2,3 These environmental contaminants are suspended in air as particulate matter for a long term and humans can be substantially exposed to PAHs around industrial activities, leading to potential health risks like cancers and cardiovascular diseases. 4,5 Hydroxylated PAHs (OH-PAHs) are newly recognized contaminants derived from hydroxylation of PAHs, which are often transformed by PAHs in living organisms. 6,7 They are commonly used as metabolic biomarkers for the

“…in positive polarity. 7,8 However, previous studies have shown that some particular molecules with conjugated structures can form radical cations (M •+ ) during ESI in positive polarity. 9,10 Polyaromatic hydrocarbons with three to seven aromatic rings were examined by Miyabayashi.…”

Section: Introductionmentioning

confidence: 99%

“…Typically, ESI generates cation adducts ([M + X] n + , X = H, Na, K, Ca, etc.) in positive polarity 7,8 . However, previous studies have shown that some particular molecules with conjugated structures can form radical cations (M •+ ) during ESI in positive polarity 9,10 .…”

Section: Introductionmentioning

confidence: 99%

Investigation on the binary ionization choices for large conjugated amines during electrospray ionization

Tan

Yin

Feng

et al. 2022

Self Cite

Rationale: Generally, amines form protonated cations ([M + H] + ) in positive polarity during electrospray ionization (ESI). However, it was found that large conjugated amines (LCAs) had binary ionization choices of generating either radical cations (M •+ ) or [M + H] + during ESI. Investigation on the mechanism would further our understanding of ESI. Methods: In this work, the binary ionization behavior of LCAs was reported and studied. Internal factors (functional groups and sizes of conjugated systems) and external factors (solvent type, flow rate, and electrode position) were systematically investigated and discussed. Results: For the internal factors, electron-donating groups and large conjugated structures of LCAs were conducive to the generation of M •+ . For the external factors, aprotic solvent, higher flow rate, and shorter distance from the electrode to the spray cone facilitated the formation of M •+ but hampered the generation of [M + H] + . Conclusion: The present study illustrated that the formations of M •+ and [M + H] +