U.S. Department of Energy

Pacific Northwest National Laboratory

Petroleomic Characterization using an Ion Mobility-Orbitrap Platform

Introduction 

Ion mobility spectrometry (IMS) is a fast gas-phase separation technique that separates ions in part based upon their shape. Different chemical classes form shape-related ‘trend lines’ in the 2D drift time-m/z chromatogram. These trend lines can be utilized as a quick diagnostic for chemical classes, and hence information that augments that from mass spectrometry. Herein we present a new IMS-Orbitrap platform that couples the benefits of drift-tube IMS with a high mass resolution Orbitrap MS. The new platform was utilized to analyze and profile an array of petroleum products, and highlights the utility of the IMS -Orbitrap platform for analysis of highly chemically complex substances.

Methods 

Samples from a number of petroleum substances across the distillation product range were dissolved into toluene/methanol mixtures. Samples were ionized by nanoESI followed by a dual funnel interface for efficient ion transfer to a home-built meter long drift tube ion mobility spectrometer interfaced to an Orbitrap MS. The ion mobility separation was synchronized with the Orbitrap acquisition for maximum ion transfer from the IMS into the Orbitrap. Hadamard multiplexing of the IMS stage and the second gate enabled highly efficient sampling of the IMS separation by the Orbitrap.

Preliminary data 

Petroleum substances are very complex and variable in chemical composition with many different chemical components with similar masses. For these reasons, multidimensional analyses with high MS resolution are important. IMS drift tubes are normally coupled with time-of-flight (TOF) MS instruments since TOF can quickly sample the IMS separation. However, TOF is limited in MS resolution so trapping instruments like Orbitrap provide important advantages for analyzing chemically complex samples. An IMS-Orbitrap platform was developed for complex sample analyses but due to the slow acquisition of Orbitrap spectra, several design modifications were required to integrate the fast IMS separation with Orbitrap. First, a dual gate design was implemented. Furthermore, due to the relatively slow speed of Orbitrap spectrum generation compared to IMS we implemented a double multiplexing scheme where a pseudorandom sequence was utilized to multiplex ion packets introduction into the drift tube as well as their sampling by the second gate. This scheme resulted in two orders of magnitude increase of ion flux into the Orbitrap as compared to conventional single packet sampling. Additionally, IMS relieved the issues associated with space charge because of the limited range of m/z species sent to the Orbitrap at every acquisition cycle. Using these advances in technology, we analyzed petroleum substances and obtained the distinct signatures of different chemical classes that constitute the makeup of each sample. Such multi-dimensional data are useful for identification and grouping of complex samples, such as petroleum substances. The addition of IMS also aids in identifying structural isomers and the growth pattern of every chemical class. These data show that our new technology enables development of petroleomics databases that contain both accurate mass (and providing elemental composition information), and accurate drift time (or collision cross section) measurements, samples can be rapidly characterized, and previously unidentified components illuminated for more in depth characterization.

Novel Aspect

A new high performance IMS-Orbitrap MS platform is described and demonstrated for efficient characterization of complex petroleum substances.

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