Super-Atmospheric Pressure Electrospray Ion Source: Applied to Aqueous Solution

Abstract

This is a follow-up paper of our previous report on an ion source, which was operated at an operating pressure higher than the atmospheric pressure. Besides having more working gas for desolvation, the reduction of mean free path of electrons in a higher pressure environment increases the threshold voltage for gaseous breakdown, thus enabling a stable electrospray for the sample solution with high surface tension without the occurrence of electric discharge. In our previous work, the ion source was not coupled directly to the mass spectrometer and significant amount of ions were lost before entering the vacuum of the mass spectrometer. In this paper, we report the new design of our second prototype in which, by using a modified ion transport capillary, the pressurized ESI ion source was coupled directly to the first pumping stage of the mass spectrometer without additional modification on the vacuum pumping system. Demonstrations of the new ion source on the sensitive detection of native proteins from aqueous solution in both positive and negative ion modes are presented.

When API Mass Spectrometry Meets Super Atmospheric Pressure Ion Sources

“…11a, the protein solvent is 2 v/v% formic acid aqueous solution which has recently become a standard reagent for the chemical digestion. Except for the peptide fragment [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], all other hydrolysis products are due to the cleavage at the Asp sites. Comparison was also done with acetic acids (Fig.…”

“…We have implemented the super-atmospheric pressure ionization MS with pure electrospray, [12][13][14][15][16] corona discharge based chemical ionization, 17) and eld desorption, 18) and had routinely run our mass spectrometer with ion source pressures ranging from several to several tens of atm. For typical analytical application where the solvent composition can be ne-tuned to best-suit the API-ESI, it is unnecessary to pressurize the ion source, though it is possible to get some signal enhancement due to higher gas throughput.…”

Super-Atmospheric Pressure Ion Sources: Application and Coupling to API Mass Spectrometer

“…Recently, we have introduced a series of high pressure ion sources implemented with electrospray, 18,19) nano and probe electrospray, [20][21][22] corona discharge chemical ionization, 23) and eld desorption. 24) ese ion sources were pressurized with air or nitrogen to a pressure higher than atmospheric pressure (p>1 atm), and were connected to API mass spectrometer via various coupling strategies.…”

“…We have previously shown that the use of pure water as solvent could be advantageous to produce very clean mass spectrum without the interference from hydrophobic contaminants dissolved in organic solvents. 19) Under super-atmospheric pressure and using water as solvent, nanoESI with a solution ow rate of ∼10 nL/min, could also be achieved using plastic pipette tips with inner diameter of ∼100 µm, which was much larger than those of standard nanoESI emitter (1-10 µm). 22) e mass spectrometer, which is designed to work with ESI and other atmospheric pressure ionization (API) source is usually referred as API mass spectrometer (API-MS).…”

“…18) In the second prototype, improvement was made by coupling the ion source directly to the mass spectrometer using a modi ed ion transport tube with smaller inner diameter (0.25 mm). 19) In this proceeding paper, we will discuss several coupling strategies and the latest prototypes that used an ion transport tube with larger i.d. (0.5 mm) incorporated with additional pumping system.…”