Direct Coupling of Normal-Phase High-Performance Liquid Chromatography to Atmospheric Pressure Laser Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry for the Characterization of Crude Oil

Abstract

The high complexity of crude oil makes the use of chromatographic separation an important tool especially for sample simplification. The coupling of normal-phase high-performance liquid chromatography (HPLC) using a polar aminocyano column to a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer offers the best attributes of good separation prior to ultrahigh resolution mass spectrometry (MS) detection. Atmospheric pressure laser ionization (APLI) was used as an ionization technique to analyze the nitrogen-containing aromatic compounds in a deasphalted crude oil due to its unique selectivity toward aromatic compounds and also due to its sensitivity. Two main chromatographic peaks were observed during this separation indicating a class-based separation. Mass spectra obtained from fractions were collected along the entire retention time and compared with each other to assign the unique constituents. By coupling the HPLC system directly to the FTICR mass spectrometer, comparable ion and UV chromatograms were obtained, reflecting the scan-to-scan sensitivity of the coupling system. The results show that it is possible to calculate reconstructed class chromatograms (RCC), allowing differences in class composition to be traced along the retention time. As an example, radical and protonated nitrogen species generated by APLI were detected along the retention time which enabled a differentiation between basic and nonbasic species in the same polar peak, thus overcoming the limitation of chromatographic resolution. This report represents the first online LC-FTICR MS coupling in the field of crude oil analysis.

Increasing Polyaromatic Hydrocarbon (PAH) Molecular Coverage during Fossil Oil Analysis by Combining Gas Chromatography and Atmospheric-Pressure Laser Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS)

“…These broad distributions are in good agreement with previous studies of fossil oils using API sources (e.g., ESI, APCI, APPI, LDI). 3,8,20,21,29,43,55–61 The broad distributions can be attributed to the large number of compounds, the chemical diversity, and the number of components per heteroatom PAH series commonly encountered in the fossil oils. The sum of all the individual mass spectrum of the GC-APLI-FT-ICR MS analysis (Figure 1, bottom red spectra) shows that, although the MS spectrum does not have the added benefit of multiple coadded transients (i.e., 25 added transients in the case of APLI-FT-ICR MS), the simplified ion population allows for sensitive detection and high mass accuracy using half of the transient time.…”

“…While prior studies have described the coupling of chromatographic separations with electron impact sources (e.g., GC-EI-TOF-MS, 38 GC-EI-QLT-Orbitrap, 39 and GC-EI-FT-ICR MS 40,41 ), more recently, the GC and LC coupling to API-FT-ICR MS has shown advantages for the detection of molecular components and the separation of isomeric components (e.g., GC-APCI-FT-ICR MS, 15,42 and HPLC-ESI/APCI/APPI/APLI-FT-ICR MS 43,44 ).…”

Gas chromatography coupled to atmospheric pressure ionization mass spectrometry (GC-API-MS): Review

“…The ionization mechanisms occurring in atmospheric pressure ionization (API) sources are of low-energy (soft), which generate spectral data typically rich in molecular or protonated molecule information. Ionization in LC/MS can be realized by electrospray ionization (ESI) [5], atmospheric pressure chemical ionization (APCI) [6] , photo ionization (APPI) [7,8], atmospheric pressure laser ionization (APLI) [9,10] and others [11,12]. In GC-MS and LC-MS different instruments are used, since in GC-MS compounds are ionized at vacuum (EI and CI) and in LC/MS at atmospheric pressure [13].…”

Analysis of Photoirradiated Water Accommodated Fractions of Crude Oils Using Tandem TIMS and FT-ICR MS

“…59, 60, 65–69 However, the biggest challenge in the coupling of liquid and gas chromatography is that it limits the FT-ICR MS analysis time, and thus the ability to better separate isobaric species, due to the slow acquisition rates needed for ultrahigh resolution mass acquisitions. 48, 65 Alternatively, other post-ionization, gas-phase separations have been proven to be a better match for FT-ICR MS analysis.…”