Accepted Oral: Prof Kim

Introduction

Ion Mobility Mass Spectrometry (IM-MS) has been proven to be a useful tool to analyze the structure of aromatic compounds in crude oils. Theoretically, IM can be used as a gas phase separation tool to isolate specific ions of interest but this approach is limited when analysing highly complex samples. This limitation can be overcome by the use of cyclic ion mobility (cIM). With cIM, multiple ion cycles, along with ion selection and reinjection, can be used to achieve improved precursor ion separation. In this study, the potential of cIM as a tool for ion separation and isolation has been explored by obtaining tandem mass spectra of individual crude oil compounds within ~0.5 m/z window.

Methods

Crude oil samples were dissolved in 100% toluene to give a concentration of 0.1 mg/mL. Samples were introduced via direct infusion, using a Harvard syringe pump, into a Waters cyclic ion mobility-enabled quadrupole time-of-flight (Q-cIM-oaToF) fitted with an atmospheric pressure photoionization (APPI) source. A sample flow rate of 5 µL/min. was used. Mass spectra were acquired over the range 50-1000 m/z. Positive ion mode APPI source settings were: repeller voltage, 0.5 kV; cone voltage, 0 V; desolvation gas flow, 600 L/hr; source temperature, 120 °C; probe temperature, 400 °C; and 2.5 mbar N2 IMS cell pressure. The cIM region was operated in an ion cycle, select and reinject sequence to effect precursor ion selection for MS/MS experiments.

Preliminary Data

The ions were first selected by the quadrupole within a 1.0 m/z window and were then further separated by use of cIM. Consequently, ions separated by ~0.1 m/z unit could be isolated and tandem mass spectrometry (MS/MS) was successfully performed on these ions. For example, the ion at 436.21 m/z was abundantly isolated despite there being a dominant ion at 436.30 m/z in the original MS spectrum. The MS/MS spectrum of the ion at 436.21 m/z was distinctively different from the MS/MS spectrum of the ion at 436.30 m/z. This proves that separation and isolation in narrow m/z windows is possible. It should be noted that obtaining MS/MS spectra for smaller ions, such the ion at m/z 436.21, is very challenging with conventional MS instruments.

A series of ions differing by two hydrogen atoms were isolated and MS/MS spectra were obtained from the ion series. It was observed that the peak distribution in MS/MS spectra shifted to smaller m/z across the series even though the m/z of the precursor ions was gradually increasing. For example, the MS/MS spectrum from C28H38 (m/z 374.2968) showed the most abundant fragmented ions at m/z 205.09, 219.11, and 233.13 whereas the spectrum from C28H46 (m/z 380.3437) showed the most abundant fragment ions at m/z 155.082, 169.096, and 183.112. The pattern observed in the spectra suggests that specific structural motifs are abundant for the crude oil compounds observed by (+) APPI MS. This is reasonable considering that crude oils compounds have been generated over millions of years and hence compounds with optimized structures may be more abundant than other compounds. Overall, the preliminary data obtained in this study proves that the cIM has great potential as a tool to isolate specific compounds of interest among complex mixture.

Novel Aspect
First study using cyclic ion mobility mass spectrometry to obtain structural information of crude oil compounds in 0.5 m/z window
Options:

A post-doc is presenting author on this abstract? No
A graduate student is presenting author on this abstract? Yes
Research advisor's name Sunghwan Kim
Advisor's email sunghwank@knu.ac.kr
An undergraduate student is presenting author on this abstract? No

Oral Choice:

Ion Mobility: New Developments & Applications
Second Oral Choice:

Instrumentation: Innovative Separations Approaches Coupled to MS
Poster:

Instrumentation: New Developments in Ion Detection

Submitting Author:

Eunji Cho
Kyungpook National University
Daegu,
eunjic@knu.ac.kr