Atmospheric‐pressure Penning ionization of aliphatic hydrocarbons

Abstract

A study has been made of the atmospheric-pressure Penning ionization (APPeI) of aliphatic hydrocarbons (pentane, hexane, heptane, and octane) with long-lived rare gas atoms (Rg*). The metastable rare gas atoms (He*, Ne*, Ar* and Kr*) were generated by the negative-mode corona discharge of atmospheric-pressure rare gases. In the Rg*APPeI mass spectra for aliphatic hyrocarbons, the relative abundances of fragment ions were found to increase in the order of He* --> Ne* --> Ar* --> Kr*. The order is in the opposite direction to the internal energies of the Rg*. The less fragmentation observed for He* may be because the nascent molecular ions [M(+.)]* formed by Penning ionization have lifetimes long enough for them to be collisionally deactivated in the atmospheric-pressure ion source. It was found that the relative abundances of fragment ions in Ar*APPeI increased when the sample pressure in the ion source was reduced. This is attributed to the collision of Ar* with molecular ions followed by fragmentation.

Desorption ionization by charge exchange (DICE) for sample analysis under ambient conditions by mass spectrometry

“…In the DAPCI spectrum (Figure 5b), however, a small peak that corresponds to the molecular ion of anthracene at m/z 178 was observed, while no molecular ion peak of anthracene was observed in the DESI spectrum (Figure 5a). DAPCI is known to generate neutral metastable species by a gas-phase electrical discharge, e.g., excited-state of ambient nitrogen, oxygen, and water etc., which can act as reagents for chemical ionization [9,15,21]. The peak for the molecular ion of anthracene as shown in Figure 5b is probably produced by a reaction between a desorbed analyte and these metastable species.…”

Rapid detection of drugs in biofluids using atmospheric pressure chemi/chemical ionization mass spectrometry

“…For example, Tsuchiya isolated the ions from the corona discharge, and ionized the liquid sample with metastable argon atoms 13, 14. For gas‐phase volatile samples, Hiraoka et al used a circular array of tungsten needles to generate the corona discharge, and the sample gas was introduced to react with the metastable argon or helium species without being exposed to the electric discharge 15, 16. In the commercial DART (Direct Analysis in Real Time) ion source,17 a more refined design of electrodes is employed to trap the ions from the corona discharge, and the metastable helium gas is further heated to assist the desorption and ionization of the sample placed between the helium source and the ion‐sampling orifice.…”

Thermal desorption metastable atom bombardment ionization aerosol mass spectrometer

“…For cases where the discharge medium is a pure gas, one can theoretically tailor conditions to yield ionization with minimal fragmentation 19 and/or to ionize only select classes of molecules. In this work we use gases with excited state energies between 8.45eV (N 2 * ) 20, 21 and 11.72eV (Ar * ), 22 which are well suited for the typical ionization energies of organic molecules (9-11eV). 23 Current literature includes reports of many new atmospheric pressure ionization schemes that rely on the controlled production of metastable species.…”

“…26,27 This work targets the analysis of aerosols vaporized in the ionization volume of the AMS, which must be maintained under high vacuum. In 1993, Faubert et al 22 In this work we have coupled a metastable beam source with an AMS to provide an instrument, termed the MAB-AMS, which measures the mass spectra of aerosol organic species with much reduced molecular fragmentation. The design of the implemented source is presented, key operating parameters are characterized, and the sensitivity and degree of fragmentation of the MAB-AMS are compared with those of the EI-AMS and of a previouslypublished VUV-AMS coupling.…”