A novel electrospray setup was found effective for direct analysis of fullerene solutions by electrospray (ES) mass spectrometry. The electrospray capillary needle used for the analysis is equipped with a thin metal (copper, platinum or stainless steel) wire installed inside the capillary. The wire tip protrudes slightly from the capillary end. In this configuration the high electrical field formed by the wire tip stimulates a specific electrospray mode with a fine spray originating from the tip. The correlation of the acquired mass spectra with the magnified view of the spray at the capillary tip was investigated. The effective formation of fullerene ions in both negative and positive ion modes was observed in mass spectra only in the specific case of the electrospray originating from the wire tip. The fullerene di-anions observed in the negative ES mass spectra provide evidence for the electrochemical nature of this process occurring at the ES capillary tip. Observation of fullerene ions in mass spectra obtained using the suggested electrospray arrangement is assumed to be a consequence of the fine spray originating from the sharp metal wire tip. In this case the liquid/metal interface is near the Taylor cone apex.
Numerical simulations of a gas flow through a capillary being a part of mass spectrometer atmospheric interface were performed using a detailed laminar flow model. The simulated interface consisted of atmospheric and forevacuum volumes connected via a thin capillary. The pressure in the forevacuum volume where the gas was expanding after passing through the capillary was varied in the wide range from 10 to 900 mbar in order to study the volume flow rate as well as the other flow parameters as functions of the pressure drop between the atmospheric and forevacuum volumes. The capillary wall temperature was varied in the range from 24 to 150 °C. Numerical integration of the complete system of Navier-Stokes equations for a viscous compressible gas taking into account the heat transfer was performed using the standard gas dynamic simulation software package ANSYS CFX. The simulation results were compared with experimental measurements of gas flow parameters both performed using our experimental setup and taken from the literature. The simulated volume flow rates through the capillary differed no more than by 10% from the measured ones over the entire pressure and temperatures ranges. A conclusion was drawn that the detailed digital laminar model is able to quantitatively describe the measured gas flow rates through the capillaries under conditions considered. Graphical Abstract ᅟ.
A two-step approach was developed for the study of ion transport in an atmospheric pressure interface. In the first step, the flow in the interface was numerically simulated using the standard gas dynamic package ANSYS CFX 15.0. In the second step, the calculated fields of pressure, temperature, and velocity were imported into a custom-built software application for simulation of ion motion under the influence of both gas dynamic and electrostatic forces. To account for space charge effects in axially symmetric interfaces an analytical expression was used for the Coulomb force. For all other types of interfaces, an iterative approach for the Coulomb force computation was developed. The simulations show that the influence of the space charge is the main contributor to the loss of ion current in the heated capillary. In addition, the maximum ion current which can be transmitted through the heated capillary (0.58 mm inner diameter and 58.5 mm length) is limited to ∼6 nA for ions with m/z = 508 Da and with reduced ion mobility 1.05 cmVs. This limit remains practically constant and independent of the ion current at the entrance of the capillary. For a particular ion type, this limit depends on its m/z ratio and ion mobility.
A laser plasma ion source was used to ionize volatile organic compounds in a gas sample. The plasma was generated on a metal target in the intermediate vacuum region of ~0.3 Torr using a pulsed Nd:YAG laser with a wavelength of 1 μm. The resulting ions mass spectra were acquired using orthogonal time‐of‐flight mass spectrometer (O‐TOF MS). When using a copper target, the ions formed are simple complexes (CuM+) of copper ions with organic molecules. The possibility of online identification of trace amounts of alkanes in nitrogen and air, with a detection limit of ~10 ppb, was demonstrated. The ionization efficiency of volatile organic compounds through the formation of clusters with metal ions is 10−4 in terms of the quasimolecular complex ions. The rate constants of ion‐molecular reactions of copper ions with octane and water molecules in nitrogen and air are estimated.
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