High-pressure Ion Source Research Articles

Generation of Ions from Aqueous Taylor Cones near the Minimum Flow Rate: "True Nanoelectrospray" without Narrow Capillary.

Generating ultrafine charged droplets using electrospray is crucial for attaining high ionization efficiency for mass spectrometry. The size of the precursor charged droplets depends on the spray flow rate, and conventional wisdom holds that an electrospray of a nL/min flow rate (nanoelectrospray) is only possible using narrow capillaries with an inner diameter of ∼1 μm or smaller. Here, the electrospray of aqueous solutions with high electric conductivities generated from a large off-line capillary of 0.4 mm i.d. has been performed using a high-pressure ion source. The electric discharge is avoided by operating the ion source at 2.5 bar gauge pressure. The highly stable Taylor cone can be tuned to a near-hydrostatic state that exhibits the "true nanoelectrospray" properties, i.e., high salt tolerance and minimal ion suppression. The Q1/2 scaling law describing the electrospray current I and flow rate Q is found to be valid down to the nanoflow regime under a condition that is free of electric discharge. For a given solution, the flow rate and the size of the initial droplets and ionization species can be controlled with the spray current as the indicator for the instantaneous flow rate without changing the emitter capillary of different sizes. In regard to the application, the nanoelectrospray with a large micropipette tip is easy to use, free of clogging when dealing with viscous and high-salt buffer solutions, and with reduced surface interaction with the emitter inner surface. An acquisition of very clean mass spectra of proteins from concentrated solutions of nonvolatile salts such as phosphate-buffered saline is demonstrated.

Experiment and theory elucidate the pathways for H3+formation in the ultrafast double ionization in methanol

Experiment and theory elucidate the pathways for H₃⁺formation in the ultrafast double ionization in methanol

Design of a Resonant Radiofrequency Driver for Ion Transmission in a Desktop Mass Spectrometer and Its Application in Volatile Organic Compound Determination

The ion transformation efficiency from a high-pressure ion source region to a low-pressure mass analysis region is one of the important indices for the mass spectrometer performance. To decrease the ion loss and improve the sensitivity of ions, a radiofrequency driver was designed in a home-made time-of-flight mass spectrometer (TOF-MS), which adopted a resistance-inductance-capacitance (RLC) resonant amplification pattern to drive the radiofrequency quadrupole (RFQ). The peak-to-peak voltage Vp-p of the radiofrequency driver was continuously adjusted from 50 to 1000 V with a relative standard deviation of 2.5‰. The performance of the radiofrequency quadrupole in the mass spectrometer was assessed by the characterization of a mixture of benzene, toluene, and p-xylene. The limits of detection for benzene, toluene, and p-xylene were 0.07, 0.05, and 0.04 ppbv, respectively. Moreover, the performance and stability of radiofrequency quadrupole were assessed by the determination of volatile organic compounds (VOCs) in newly decorated rooms and exhaled breath. The results indicated that the developed radiofrequency driver has potential for use in mass spectrometers.

Super-atmospheric pressure ionization mass spectrometry and its application to ultrafast online protein digestion analysis.

Pressure is a key parameter for an ionization source. In this Special Feature article, Lee Chuin Chen and colleagues review super-atmospheric pressure ionization MS with electrospray, corona-discharge-based chemical ionization, and field desorption. They routinely run their mass spectrometer with ion source pressures ranging from several to several tens of atmospheres. A number of strategies have been used to preserve the high vacuum of the instrument while working with a high-pressure (HP) ion source. A recent prototype uses a booster pump with variable pumping speed added to the first pumping stage of the mass spectrometer to regulate a constant vacuum pressure. Further, a new HP-ESI source allowing rapid (a few seconds) online protein digestion MS is also reported. Dr. Lee Chuin Chen is Associate Professor in the Department of Interdisciplinary Research at the University of Yamanashi (Yamanashi, Japan). His main research interest is the development of novel mass spectrometric methods for in-situ medical diagnosis.

Studies of the mechanism of the cluster formation in a thermally sampling atmospheric pressure ionization mass spectrometer

In this study a thermally sampling atmospheric pressure ionization mass spectrometer is described and characterized. The ion transfer stage offers the capability to sample cluster ions at thermal equilibrium and during this transfer fundamental processes possibly affecting the cluster distribution are also readily identified. Additionally, the transfer stage combines optional collision-induced dissociation (CID) analysis of the cluster composition with thermal equilibrium sampling of clusters. The performance of the setup is demonstrated with regard to the proton-bound water cluster system. The benefit of the studied processes is that they can help to improve future transfer stages and to understand cluster ion reactions in ion mobility tubes and high-pressure ion sources. In addition, the instrument allows for the identification of fragmentation and protonation reactions caused by CID.

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

Pressurizing the ionization source to gas pressure greater than atmospheric pressure is a new tactic aimed at further improving the performance of atmospheric pressure ionization (API) sources. In principle, all API sources, such as ESI, APCI and AP-MALDI, can be operated at pressure higher than 1 atm if suitable vacuum interface is available. The gas pressure in the ion source can have different role for different ionization. For example, in the case of ESI, stable electrospray could be sustained for high surface tension liquid (e.g., pure water) under super-atmospheric pressure, owing to the absence of electric discharge. Even for nanoESI, which is known to work well with aqueous solution, its stability and sensitivity were found to be enhanced, particularly in the negative mode when the ion source was pressurized. For the gas phase ionization like APCI, measurement of gaseous compound also showed an increase in ion intensity with the ion source pressure until an optimum pressure at around 4-5 atm. The enhancement was due to the increased collision frequency among reactant ion and analyte that promoted the ion/molecule reaction and a higher intake rate of gas to the mass spectrometer. Because the design of vacuum interface for API instrument is based on the upstream pressure of 1 atm, some coupling aspects need to be considered when connecting the high pressure ion source to the mass spectrometer. Several coupling strategies are discussed in this paper.

Mass Spectrometric Study of Positive Ion-Molecule Reactions in the C3H6and Ar Mixtures Inside the High Pressure Ion Source

Ion molecule reactions have been measured for the propene argon mixtures of di erent compositions using a quadrupole mass spectrometer with a high-pressure ion source. The concentration of propane in these mixtures ranged from 10% to 90% (at 10% increment). The following primary and secondary ions: CH+5 (m/q = 17), C2H + 2 (m/q = 26), C2H + 3 (m/q = 27), C2H + 4 (m/q = 28), C2H + 5 (m/q = 29), C3H + 3 / Ar (m/q = 39), C3H + 4 / Ar (m/q = 40), C3H + 5 (m/q = 41), C3H + 6 / Ar (m/q = 42), C3H + 7 (m/q = 43), C3H + 8 (m/q = 44), C4H + 5 (m/q = 53), C4H + 6 (m/q = 54), C4H + 7 (m/q = 55), C4H + 8 (m/q = 56), C4H + 9 (m/q = 57), C5H + 5 (m/q = 65), C5H + 6 (m/q = 66), C5H + 7 (m/q = 67), C5H + 8 (m/q = 68), C5H + 9 (m/q = 69), C5H + 10 (m/q = 70) were observed. Relative ion current intensities for primary and secondary ions are presented as a function of both total mixtures pressure and concentration of propene in the mixture. Primary ions were produced by electrons with the energy of 300 eV. The potential of repeller electrode VR inside the ion source collision chamber was xed at 5 V for all measurements. The total mixture pressure was changed from 0.7 to 26.6 Pa. Schemes of ion molecule reactions were proposed.

High-Pressure Study of Ion-Molecule Reactions in the Mixture of Carbon Tetrafluoride and Argon

Charge-exchange ion molecule reactions of Ar ions with CF4 have been studied in the pressure range 1.33 39.99 Pa. A quadrupole mass spectrometer with a high-pressure ion source has been used for measuring gaseous ion molecule reactions in the mixture of 1% CF4 and 99% Ar. The fractional abundance Ii/ ∑ Ii of the observed CF+3 , CF + 2 and argon ions has been determined as a function of the gas mixture pressure (at the values of the repeller electrode potentials VR ranging from 2 to 10 V).

High pressure mass-spectrometric investigations of ion–molecule reactions in propane and argon mixtures

Ion–molecule reactions initiated by electron impact in the propane–argon mixtures have been studied by a quadrupole mass spectrometer with a high pressure ion source. The total gas pressure of investigated mixtures was 1.33 Pa. The influence of repeller potential on the ion–molecule reactions has been studied. The repeller potential was changed in the range 2–12 V. Measurements were performed for different concentrations of propane in the mixture with argon (from 10% C3H8 + 90% Ar to 90% C3H8 + 10% Ar with 10% propane increments). The major ion–molecule reactions have been identified. The primary ions produced in the gas by the electrons with the energy of 300 eV and the secondary ones from the ion–molecule reactions were observed. Relative intensities for primary and secondary ions are presented as a function of potential of the repeller electrode and concentration of propane in the mixtures with argon.

Ion Molecule Reactions between Ligated Transition Metal Cations with Methane, Ethane and Propane in a High Pressure Ion Source

The reactions of CH4, C2H6 and C3H8 with [η5-C5H5M(CO) n]+ (M = Fe, Co and Ni; 0 ≤ n ≤ 2) in the gas phase have been studied using a double focusing mass spectrometer with a high pressure ion source (HPIS). The products observed are mainly described as weakly bound ion molecule complexes. Carbon–hydrogen bond insertions were observed with propane and only to a minor extent with ethane. Methane was found to form ion molecule complexes only with ligated transition metal cations. The reactivity was influenced by the number of carbonyl ligands and the metal cations. The main adducts formed were obtained when one or no CO ligands were bound to the cyclopentadienyl metal cation. No adducts between the alkanes and naked transition metal cations or protonated metal compounds were found.

ChemInform Abstract: Gas-Phase Oxidation of Group 6 Metal Carbonyl Anions

Oxidation of Cr(CO) 5 - , Mo(CO) 5 - , and W(CO) 5 - was examined in a low-pressure (∼5×10 -8 mbar) and a high-pressure external(∼3.5 mbar) environment using a Fourier-transform ion cyclotron resonance spectrometer equipped with a high-pressure external ion source. Although the oxidation chemistry displayed by the Cr and W systems was fairly similar, the Mo analogue had several unique features. In addition, remarkable differences were observed between high- and low-pressure oxidation

High-pressure investigations of positive ion-molecule reactions in a mixtureof H 2S and CH 4

The positive ion-molecule reactions in the mixtures of hydrogen sulfide and methane have been examined by means of quadrupole mass spectrometer with the high-pressure ion source. The concentration of hydrogen sulfide in mixtures ranged from 10% to 90% with 10% increment. For each mixture major bimolecular ion-molecule reactions have been identified in the total pressure range from 0.7 to 33.3 Pa. The electron energy for all measurements was fixed at 300 eV and the repeller potential was maintained at 5 V. Relative intensities of ion currents for the observed ions C +, CH +, CH 2 +, CH 3 +, CH 4 +, CH 5 +, C 2H 3 +, C 2H 4 +, C 2H 5 +, S +, HS +, H 2S +, H 3S +, H 3 34S +, CHS +, CH 3S +, S 2 +, HS 2 + and H 2S 2 + were determined as a function of total gas pressure inside the ion source collision chamber, repeller potential and concentration of methane in the mixture.

Ion–molecule reactions in mixtures of ethane with carbon tetrafluoride

Ion–molecule reactions have been measured for the ethane–carbon tetrafluoride mixtures of different compositions using a quadrupole mass spectrometer with a high-pressure ion source. Concentration of ethane in these mixtures ranged from 10% to 90% (at 10% increment). The following primary and secondary ions: CH 3 +, F +, C 2H 3 +, C 2H 4 +, C 2H 5 +, C 2H 6 +, C 3H 5 +, C 3H 7 +, C 4H 7 +, C 4H 9 +, C 4H 10 +, C 4H 11 + and CF 3 + were observed. Relative ion current intensities for primary and secondary ions are presented as a function both of total mixture pressure and concentration of carbon tetrafluoride in the mixture. Primary ions were produced by electrons with the energy of 300 eV. Potential of repeller electrode inside the ion source collision chamber was fixed at 5 V for all measurements. The total mixture pressure was changed from 0.7 to 26.6 Pa. Schemes of ion–molecule reactions were proposed.

High pressure investigations of ion – Molecule reactions in a mixture of C 3H 8 and Ne

The gas phase reactions of positive Ne + ions produced from neon with neutral propane have been studied with the use of a quadrupole mass spectrometer with a high pressure ion source. The measurements were performed in a mixture of 1% C 3H 8 and 99% Ne in the pressure range 1.33–40.00 Pa. The fractional abundances I i/Σ I i (relative intensity of the ion currents) of dominant C 2H 2 +, C 2H 3 +, C 2H 4 +, C 2H 5 +, C 3H 5 +, C 3H 7 + ions and neon ions have been determined as a function of the gas mixture pressure and of the repeller electrode potential ranged from 3 V to 10 V.

Influence of repeller potential on ion–molecule reactions in methane and carbon tetrafluoride mixtures

Investigations of ion–molecule reactions were performed for methane–carbon tetrafluoride mixtures of different compositions. Concentration of methane in these mixtures ranged from 10% to 90% (at 10% increment) and total mixture pressure was fixed at 13.3 Pa. Measurements were made using a quadrupole mass spectrometer with a high-pressure ion source. Primary ions CH 4 +, F +, CF + and CF 3 + were produced by electrons with energy of 300 eV. Secondary ions CH 5 +, C 2H 3 +, C 2H 4 +, C 2H 5 +, C 2H 7 + and CF 3 + were observed as the result of ion–molecule reactions. The influence of repeller potential on ion–molecule reactions efficiency was examined.

A high-pressure mass spectrometric study of ion–molecule reactions in a mixture of CF 4 and He

Gas phase ion–molecule reactions of positive He + ions produced from helium with neutral carbon tetrafluoride have been studied. The measurements were made with a quadrupole mass spectrometer with a high-pressure ion source. The fractional abundance I i /∑ I i of dominant ions CF 3 +, CF 2 + and helium ions has been determined as a function of the (1% CF 4 and 99% He) gas mixture pressure (in the range 1.33–31.92 Pa) and of the repeller electrode potential (ranging from 3 to 10 V).

High-pressure mass spectrometric investigations of ion–molecule reactions in hydrogen sulfide and ammonia mixtures

The positive ion–molecule reactions in the mixtures of hydrogen sulfide and ammonia have been examined by means of quadrupole mass spectrometer with high-pressure ion source. The concentration of hydrogen sulfide in mixtures ranged from 10% to 90% with 10% increment. Mainly observed primary ions: NH 2 + ( m/ q=16), NH 3 + ( m/ q=17), S + ( m/ q=32) and H 2S + ( m/ q=34) were formed as the result of ionization and dissociative ionization by electrons with energy of 300 eV. For each mixture, major bimolecular ion–molecule reactions have been identified at total pressure from 0.5 to 33.3 Pa. The main secondary ions: NH 4 + ( m/ q=18), H 3S + ( m/ q=35) and NH 3S + ( m/ q=49) were observed. Relative intensities of ion currents for observed ions were determined as a function of total gas pressure inside ion source collision chamber, repeller potential and concentration of hydrogen sulfide in the mixture.

Ion–molecule reactions in mixtures of methane with carbon tetrafluoride

Ion–molecule reactions have been measured for methane–carbon tetrafluoride mixtures of different composition using a quadrupole mass spectrometer with a high-pressure ion source. Concentration of methane in these mixtures ranged from 10% to 90% (at 10% increment). Primary ions CH 3 + , CH 4 + , F + , CF + and CF 3 + were produced by electrons with energy of 300 eV. Secondary ions CH 5 + , C 2 H 3 + , C 2 H 4 + , C 2 H 5 + , C 2 H 7 + and CF 3 + were observed as the result of ion–molecule reactions. Relative current intensities for primary and secondary ions are presented as a function of both total mixture pressure and concentration of methane in the mixture. Potential of repeller electrode inside the ion source collision chamber was fixed at 5 V for all measurements. Total mixture pressure was changed from 0.7 to 33.3 Pa. Schemes of ion–molecule reactions were proposed.

Mass spectrometric study of ion/molecule reaction in methane and ammonia mixtures

Ion/molecule reactions initiated by electron impact in ammonia–methane mixtures have been studied by means of quadrupole mass spectrometer with a high-pressure ion source. The total pressure of the mixtures was ranged from 0.5 to 33.3 Pa. Measurements were performed for different concentrations of ammonia and methane in the mixture (from 10% CH 4+90% NH 3 to 90% CH 4+10% NH 3 with 10% increment). The major ion/molecule reactions have been identified. Relative ion intensities for the observed ions were determined as a function of total gas pressure inside the ion source collision chamber and concentration of methane in the mixture.

Ion–molecule reaction in pure H 2S

The results of investigation of ion–molecule reaction in pure hydrogen sulfide are presented. Measurements were performed by means of quadrupole mass spectrometer with a high-pressure ion source. The primary ions S +, HS +, H 2S + were formed as the result of ionization and dissociative ionization of neutral H 2S by electrons with energy 300 eV. They react with neutral hydrogen sulfide to form secondary ions H 3S +, S 2 +, H 2S 2 +, H 5S 2 + and H 2S 3 +. Small amounts of H 3 34S 2 + were also observed. Relative ion currents for the observed ions were determined as a function of total H 2S pressure inside the ion source collision chamber. The reaction rate constants for S +, HS + and H 2S + were determined.