Rhapso: Automatic Stitching of Mass Segments from Fourier Transform Ion Cyclotron Resonance Mass Spectra

Abstract

Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) provides the resolution and mass accuracy needed to analyze complex mixtures such as crude oil. When mixtures contain many different components, a competitive effect within the ICR cell takes place that hampers the detection of a potentially large fraction of the components. Recently, a new data collection technique, which consists of acquiring several spectra of small mass ranges and assembling a complete spectrum afterward, enabled the observation of a record number of peaks with greater accuracy compared to broadband methods. There is a need for statistical methods to combine and preprocess segmented acquisition data. A particular challenge of quadrupole isolation is that near the window edges there is a drop in intensity, hampering the stitching of consecutive windows. We developed an algorithm called Rhapso to stitch peak lists corresponding to multiple different m/z regions from crude oil samples. Rhapso corrects potential edge effects to enable the use of smaller windows and reduce the required overlap between windows, corrects mass shifts between windows, and generates a single peak list for the full spectrum. Relative to a stitching performed manually, Rhapso increased the data processing speed and avoided potential human errors, simplifying the subsequent chemical analysis of the sample. Relative to a broadband spectrum, the stitched output showed an over 2-fold increase in assigned peaks and reduced mass error by a factor of 2. Rhapso is expected to enable routine use of this spectral stitching method for ultracomplex samples, giving a more detailed characterization of existing samples and enabling the characterization of samples that were previously too complex to analyze.

Narrow Aperture Detection Electrodes ICR Cell with Quadrupolar Ion Detection for FT-ICR MS at the Cyclotron Frequency

“…52 Further method development, particularly segmented data acquisition and processing, should provide an additional performance boost as demonstrated by Barrow and co-workers, and others. 24,53,54 Other modern method developments, including the use of on-line liquid separation of petroleum-type samples should reveal even more molecular features, as suggested by an approach spearheaded by Rodgers and co-workers. 55 Therefore, a combination of modern methods should be employed to comprehensively benchmark the 2xNADEL ICR cell at the true cyclotron frequency to evaluate its standing and value in the contemporary petroleomics field.…”

Online Counter Gradient LC-FT-ICR-MS Enables Detection of Highly Polar Natural Organic Matter Fractions

“…Next to full mass range acquisition, Q-isolation for selected mass ranges (CASI, continuous accumulation of selected ions) was used to detect low-abundant ions. Q-isolation with subsequent mass window stitching is suitable for LC-MS runs to accumulate ions of selected mass spectral windows in the hexapole concomitant to ion detection in the cell . Ten mass windows with window sizes of 50 to 100 Da were used along the mass range of DOM peaks (150–1000 mz) by multiple injections on the LC system and sequential acquisition of mass windows by the FT-ICR-MS. A higher IAT of 400 ms was used to increase the number of ions in the cell as compared to the full scan mode.…”

Segment Scan Mass Spectral Acquisition for Increasing the Metabolite Detectability in Chemical Isotope Labeling Liquid Chromatography–Mass Spectrometry Metabolome Analysis

“…Reducing the segment width does not increase the dynamic range of detection if the composition of the trapped ions is relatively simple. Thus, the segment scan method benefits the most for analyzing very complex samples, as eloquently demonstrated in DI-MS analysis of petrochemicals and metabolome samples. − In this regard, when chemical derivatization is used to improve the metabolite detectability in CIL LC–MS, many more metabolites from urine become ionizable. As a result, a significant increase in the number of peak pairs detected can be achieved when the segment scan is used even when LC is used to reduce the number of coeluting metabolites from the urine sample.…”

“…There are several studies showing the significant benefits gained by using segment scan over full scan, particularly in the areas of petroleomics , and metabolomics, ,, although extra time may be required to perform multiple segment scans. Petrochemicals such as crude oils are one of the most complex sample types.…”