Vacuum Laser Photoionization inside the C-trap of an Orbitrap Mass Spectrometer: Resonance-Enhanced Multiphoton Ionization High-Resolution Mass Spectrometry

Abstract

State-of-the-art mass spectrometry with ultraviolet (UV) photoionization is mostly limited to time-of-flight (ToF) mass spectrometers with 1000–10 000 m/Δm mass resolution. However, higher resolution and higher spectral dynamic range mass spectrometry may be indispensable in complex mixture characterization. Here, we present the concept, implementation, and initial evaluation of a compact ultrahigh-resolution mass spectrometer with gas-phase laser ionization. The concept is based on direct laser photoionization in the ion accumulation and ejection trap (C-trap) of an Orbitrap mass spectrometer. Resonance-enhanced multiphoton ionization (REMPI) using 266 nm UV pulses from a frequency-quadrupled Nd:YAG laser was applied for selective and efficient ionization of monocyclic and polycyclic aromatic hydrocarbons. The system is equipped with a gas inlet for volatile compounds and a heated gas chromatography coupling. The former can be employed for rapid system m/z-calibration and performance evaluation, whereas the latter enables analysis of semivolatile and higher-molecular-weight compounds. The capability to evaluate complex mixtures is demonstrated for selected petrochemical materials. In these experiments, several hundred to over a thousand compounds could be attributed with a root-mean-square mass error generally below 1 ppm and a mass resolution of over 140 000 at 200 m/z. Isobaric interferences could be resolved, and narrow mass splits, such as 3.4 mDa (SH4/C3), are determined. Single laser shots provided limits of detection in the 20-ppb range for p-xylene and 1,2,4-trimethylbenzene, similar to compact vacuum REMPI-ToF systems.

Simultaneous on-line vacuum single- and multi-photon ionization on an orthogonal acceleration time-of-flight mass spectrometer platform

“…This has already be proven with a vacuum ionization Orbitrap-REMPI development serving for a resolving power of up to 140 000 at a mass of 200 m / z . 49…”

“…This has already be proven with a vacuum ionization Orbitrap-REMPI development serving for a resolving power of up to 140 000 at a mass of 200 m/z. 49 In this example, the sensitivity of the instrument is enhanced by a factor of two. The approach is still untargeted.…”

Review on Evolved Gas Analysis Mass Spectrometry with Soft Photoionization for the Chemical Description of Petroleum, Petroleum-Derived Materials, and Alternative Feedstocks

“…Here, high-resolution mass spectrometry allowed for the resolution of narrow mass splits within the spectra of the fossil petroleum matrices, allowing confident assignment of the signals toward the alkylated homologue rows of various polycyclic aromatic hydrocarbons (PAHs) (Figure ). Very recently, light crude oil (CPC blend from Kazakhstan) was characterized on the molecular level by newly introduced atmospheric pressure single-photon laser ionization (APSPLI). In this work, we conclude that the novel APSPLI concept is able to ionize a broad compositional space, particularly useful for the description of petroleum matrices …”

“…The compound classes are color-coded. This figure was reprinted with permission from ref . Copyright 2021 American Chemical Society.…”

Addressing Thermal Behavior and Molecular Architecture of Asphaltenes by a Thermal-Optical Carbon Analyzer Coupled to High-Resolution Mass Spectrometry

“…As the molecular architecture strongly influences the coking behavior of a given heavy residue or asphaltene fraction, we hypothesize that the organic and elemental carbon values serve as an overview measure, thus giving an indirect descriptor for the predominant asphaltene structural motif. Analysis of the evolved gas mixture is carried out by a recently introduced Orbitrap high-resolution mass analyzer equipped with sensitive and soft vacuum photoionization . Particularly, photoionization techniques have shown to be less prone to matrix effects and ion suppression, with vacuum ionization schemes at the forefront revealing a low bias.…”