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An advanced mass spectrometry (MS) technique developed by chemists at the University of Warwick, Coventry, U.K., has broken a world record for the number of molecular compositions identified in a single sample of petroleum.
Known as operation at constant ultrahigh resolution (OCULAR), it combines experimental and data processing techniques that allowed the chemists to characterize the most-complex sample they have ever worked on — a non-distillable heavy petroleum fraction. They managed to assign a record-breaking number of 244,779 molecular compositions within a single sample of the fraction.
Identifying the elemental composition of such molecules can provide valuable data for research, determine the mixture’s viability for use in the petrochemical industry, or even “fingerprint” a complex mixture such as oil or environmental samples, say the chemists.
To date, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has represented the state-of-the-art, offering the highest performance in terms of both resolving power and mass accuracy. However, very complex mixtures have always posed a serious challenge to the technology.
The Warwick chemists start with an analysis of a sample of heavy petroleum in solution using FT-ICR MS. Then the molecules in the sample are ionized, excited and detected using a Bruker solariX FT-ICR MS to determine the mass-to-charge ratios.
Figure 1. The FT-ICR MS instrument used by University of Warwick chemists has proved a record-breaking new analytical method for fingerprinting petroleum and other complex mixtures. Source: University of Warwick, Department of Chemistry.
What they are doing is effectively “filtering” the ions that go to the FT-ICR cell for detection. This means they have plenty of ions per peak, but not so many in total to cause the problems traditionally associated with complex samples. This allows them to build a complete data set in stages — and to detect the very “weak” (i.e., low abundance) compounds, too.
Key here is the ability to keep the resolving power the same for each segment being analyzed. Then, an algorithm looks at the segments to find the best place to overlap them. It ultimately stitches them together in one very complex data set. The approach opens new doors, particularly for complex samples.
Diana Palacio Lozano, from Warwick’s Department of Chemistry, notes: “This method can improve the performance of a range of FTMS instruments, including high and low magnetic field FT-ICR MS instruments and [ion trap mass analyzer] Orbitrap instruments. We are now able to analyze mixtures that, due to their complexity, are challenging even for the most powerful analytical techniques. This technique is flexible as the performance can be selected according to the research needs.”
The heavier oil’s extraordinarily complex elemental composition now explains its low volatility. The high complexity of heavy oils can interfere with catalysis and affects extraction, transport and refining processes. The OCULAR technique also is powerful enough for samples requiring the highest performance to assign compositions based on mass accuracy or fine isotopic patterns.
Principal investigator Mark Barrow says: “The OCULAR approach allows us to push the current analytical limits for characterizing the most complex samples. It significantly extends the performance of all FTMS instruments at no additional cost and works well with developments in the field, such as newer hardware designs, detection methods, and data processing methods. OCULAR is highly versatile, the experiments and processing can be adapted as needed, and the approach can be applied to many research areas, including energy, healthcare and the environment.”
Examples for analysis and potential applications include energy, for example petroleum and biofuels; life sciences and healthcare, e.g., proteomics, cancer research, and metabolomics; materials such as polymers; and environmental analysis, including “fingerprinting” oil spills by their molecular composition.
The Warwick chemists now are applying the methodology to other sample types within their laboratory, such as petroleum and bio-oils/biofuels, and reviewing ways to further develop their OCULAR approach.
“The non-distillable sample we tackled was one of the most challenging we have ever tried to analyze, and the OCULAR approach made the difference between getting no useful data and producing the most complex petroleum spectrum to date,” he says, adding, “ So we soon realized the methodology would hold promise for industry and can be particularly useful for the heaviest and most complex samples.”
Although he couldn’t go into details, Barrow revealed that industry has already expressed interest in the method and its results.
Seán Ottewell is Chemical Processing's Editor at Large. You can email him at [email protected].
