Incorporation of a flared inlet capillary tube on a Fourier transform ion cyclotron resonance mass spectrometer

Abstract

Flared inlet capillary tubes have been coupled with a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer to help the ion transmission from the atmospheric pressure to the first vacuum region. We investigated different types of atmospheric pressure ionization methods using flared inlet tubes. For most of the ionization methods, such as ESI and DESI, increased ion current transmitted from the atmospheric pressure ion source to the first stage vacuum system was observed with the use of our enhanced ion inlet designs. The corresponding ion intensity detected on a FT-ICR mass spectrometer was also observed to increase two-to fivefold using ESI or DESI with the flared tube inlet. Moreover, increased spray tip positional tolerance was observed with implementation of the flared inlet tube. We also include our preliminary results obtained by coupling AP-MALDI with flared inlet tube in this paper. For AP-MALDI, the measured ion current transferred through the flared inlet tube was about 2 to 3 times larger than the ion current through the control non- and atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI), have been widely used with mass spectrometry for proteomics studies [1][2][3][4][5]. Desorption electrospray ionization (DESI) is an exciting new atmospheric pressure desorption ionization method introduced by Cooks et al. [6,7]. Charged solvent droplets are sprayed directly onto an analyte surface through a pneumatically-assisted electrospray ion source. This new method is very attractive due to its utility for direct analysis of different compounds on a variety of surface types [6 -8], and will enable application of mass spectrometry to more diverse, more challenging analytical problems. For all these ionization methods, the ions generated under ambient conditions are transferred through an atmospheric pressure interface such as an inlet tube or an orifice followed by several stages of differential pumping and then ions are sent to the MS detector [1][2][3].A common hurdle encountered in the implementation of any atmospheric ion source is related to the transfer of ions produced at atmospheric pressure to the low vacuum mass analyzer. For all these atmospheric pressure ion sources, the gas-phase ions produced at atmospheric pressure are transferred to the lower pressure regions through conductance limits such as a metal capillary or an orifice [9,10]. For electrospray ionization, it has been reported that gas-phase collisions and charge-charge repulsion after ion formation lead to an expansion of the ion cloud [3,11]. In AP-MALDI and DESI, ions are also dispersed once created at atmospheric pressure. Since ions must enter the MS through a small aperture or capillary with limited cross section, the ion cloud expansion and dispersion can significantly decrease the ion transmission to the lower pressure region, and thus decrease the sensitivity of the analysis. It has also been reported that the ion transmission efficiency between the ESI emitter and the inlet of the mass spectr...

Antioxidant Pathways and One‐Electron Oxidation of Dopamine and Cysteine in Electrospray and On‐Line Electrochemistry Electrospray Ionization Mass Spectrometry

“…The spray needle was biased at þ 3 kV. A cone-shaped capillary inlet [36] (508 divergence angle from 1.58 mm i.d. to 6.13 mm orifice diameter) was used.…”

Characterizing Electrospray Ionization Using Atmospheric Pressure Ion Mobility Spectrometry

“…Consequently only a small portion of total ions can be transported into the MS inlet by dynamic gas flow and potential difference imposed between the spray emitter and the MS inlet (Figure 3). Efforts to increase the size of MS entrance with the use of multicapillary inlet 31 or flared inlet tube 32 have been reported to obtain better sampling efficiency. However, there is an upper limit for the MS inlet size since higher pump speed is needed to maintain the low pressure as MS inlet size increases.…”

One‐Electron Oxidation and Sensitivity of Uric Acid in On‐Line Electrochemistry and in Electrospray Ionization Mass Spectrometry

“…A conical inlet capillary [16] ESI MS system ( Fig. 1), which was recently used for studies of small metabolites [14], was used in the measurements of uric acid.…”

“…Low m/z ions of biological metabolites, such as uric acid, are radially distributed in the electrospray and are thus segregated in the standard cylindrical inlet ESI MS, which results in low sensitivity of detection. The expected enhancement of sensitivity was realized because of the improved collection and subsequent desolvation of ions at a large conical inlet capillary compared to a standard cylindrical capillary inlet [16]. Positive ion mode ESI MS was used in this work because of its high sensitivity to protonated analytes.…”