Application of laser photofragmentation-resonance enhanced multiphoton ionization to ion mobility spectrometry

Abstract

We demonstrate detection of nitro-containing compounds with laser photofragmentation (PF) coupled with resonance enhanced multiphoton ionization (REMPI) and ion mobility spectrometry (IMS). In PF-REMPI, a laser dissociates the parent molecules, producing fragments that can then be ionized by absorption of additional laser photons. The production of these ions strongly depends on the wavelength of laser light, with ion yields corresponding to the absorption spectrum of the fragments [nitric oxide (NO) in the present case]. Combining IMS with PF-REMPI provides further specificity, separating ions according to their mobilities through an atmospheric-pressure drift tube. In this work, we use a pulsed UV laser to examine the characteristics of atmospheric-pressure PF-REMPI, the chemistry occurring in the ionization region and drift tube, and the viability of detecting ions created by both resonance-enhanced and nonresonant ionization. Probing NO in a helium-nitrogen bath, we demonstrate that the detection of ions displays single-shot response to changes in ion generation, with an ion extraction-to-collection efficiency of approximately 12%. We then evaluate the sensitivity and specificity of PF-REMPI/IMS as applied to the detection of both the explosive surrogate 2, 4-dinitrotoluene and the nuisance compound nitrobenzene.

Photodegradation of Flutamide and Halogen Derivatives of Nitrobenzotrifluoride: The NO Release Channel

“…The laser flux was optimized such that signal intensity for the NO fragment was observed only in the presence of both the pump and probe lasers and was absent with either the probe or pump lasers (Figure S1, see the Supporting Information). The NO radicals thus formed (IP = 9.26 eV) were resonantly probed using a 213 nm (5.82 eV) laser utilizing the (X 2 Π) → (A 2 Σ + ) [(1,0); P 1′ ( J = 50.5)] transition region of the NO radical. ,− The velocity mapped images of the NO photofragment were collected in the pump–probe configuration by appropriately time gating the front plate of the detector. The images were acquired by raw imaging mode (up to 100,000 laser shots) with NuAcq software and the images were quadrant-symmetrized using ImageJ .…”

Selective ionization of marker molecules in fuels by laser-based ion mobility spectrometry (LIMS)

“…photofragmentation, charge transfer reaction monitoring, trace detection and aromatics sensing. [31][32][33][34][35][36] In this study, we present qualitative and quantitative analysis of markers in fuels (petrol/diesel) using REMPI-IM spectrometry without chromatographic pre-separation. Fuel as a complex matrix with many PAHs required the use of laser wavelengths above 300 nm, or even 350 nm to obtain easily interpretable marker signals.…”

Negative photoionization chloride ion attachment ion mobility spectrometry for the detection of organic acids

“…Unfortunately, the radioactive source has serious disadvantages including a limited linear range, inexible selectivity, and the regulatory requirements associated with radioactive material. Recently, non-radioactive ion sources, such as ultraviolet radiation (UV) photoionization source, 11,12 corona discharge, 13,14 electrospray ionization, 15,16 surface ionization, 17,18 laser ionization, 19,20 and X-ray ionization 21 have been developed.…”