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See detailHighly Multiplexed Targeted Proteomics Acquisition on a TIMS-QTOF
Lesur, Antoine; Schmit, Pierre-Olivier; Bernardin, François et al

in Analytical Chemistry (2021)

Targeted proteomics allows the highly sensitive detection of specific peptides and proteins in complex biological samples. Here, we describe a methodology for targeted peptide quantification using a ... [more ▼]

Targeted proteomics allows the highly sensitive detection of specific peptides and proteins in complex biological samples. Here, we describe a methodology for targeted peptide quantification using a trapped ion mobility quadrupole time-of-flight mass spectrometer (timsTOF Pro). The prm-PASEF method exploits the multiplexing capability provided by the trapped ion mobility separation, allowing more than 200 peptides to be monitored over a 30 min liquid chromatography separation. Compared to conventional parallel reaction monitoring (PRM), precursor ions are accumulated in the trapped ion mobility spectrometry (TIMS) cells and separated according to their shape and charge before eluting into the quadrupole time-of-flight (QTOF) part of the mass spectrometer. The ion mobility trap allows measuring up to six peptides from a single 100 ms ion mobility separation with the current setup. Using these improved mass spectrometric capabilities, we detected and quantified 216 isotope-labeled synthetic peptides (AQUA peptides) spiked in HeLa human cell extract with limits of quantification of 17.2 amol for some peptides. The acquisition method is highly reproducible between injections and enables accurate quantification in biological samples, as demonstrated by quantifying KRas, NRas, and HRas as well as several Ras mutations in lung and colon cancer cell lines on fast 10 min gradient separations. [less ▲]

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See detailDevelopment and Application of Liquid Chromatographic Retention Time Indices in HRMS-Based Suspect and Nontarget Screening
Aalizadeh, Reza; Alygizakis, Nikiforos A.; Schymanski, Emma UL et al

in Analytical Chemistry (2021), 93(33), 11601--11611

There is an increasing need for comparable and harmonized retention times (tR) in liquid chromatography (LC) among different laboratories, to provide supplementary evidence for the identity of compounds ... [more ▼]

There is an increasing need for comparable and harmonized retention times (tR) in liquid chromatography (LC) among different laboratories, to provide supplementary evidence for the identity of compounds in high-resolution mass spectrometry (HRMS)-based suspect and nontarget screening investigations. In this study, a rigorously tested, flexible, and less system-dependent unified retention time index (RTI) approach for LC is presented, based on the calibration of the elution pattern. Two sets of 18 calibrants were selected for each of ESI+ and ESI-based on the maximum overlap with the retention times and chemical similarity indices from a total set of 2123 compounds. The resulting calibration set, with RTI set to range between 1 and 1000, was proposed as the most appropriate RTI system after rigorous evaluation, coordinated by the NORMAN network. The validation of the proposed RTI system was done externally on different instrumentation and LC conditions. The RTI can also be used to check the reproducibility and quality of LC conditions. Two quantitative structure−retention relationship (QSRR)-based models were built based on the developed RTI systems, which assist in the removal of false-positive annotations. The applicability domains of the QSRR models allowed completing the identification process with higher confidence for substances within the domain, while indicating those substances for which results should be treated with caution. The proposed RTI system was used to improve confidence in suspect and nontarget screening and increase the comparability between laboratories as demonstrated for two examples. All RTI-related calculations can be performed online at http://rti.chem.uoa.gr/. [less ▲]

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See detailFragment Formula Calculator (FFC): Determination of chemical formulas for fragment ions in mass spectrometric data
Wegner, André UL; Weindl, Daniel UL; Jäger, Christian UL et al

in Analytical Chemistry (2014), 86(4), 22212228

The accurate determination of mass isotopomer distributions (MID) is of great significance for stable isotope-labeling experiments. Most commonly, MIDs are derived from gas chromatography/electron ... [more ▼]

The accurate determination of mass isotopomer distributions (MID) is of great significance for stable isotope-labeling experiments. Most commonly, MIDs are derived from gas chromatography/electron ionization mass spectrometry (GC/EI-MS) measurements. The analysis of fragment ions formed during EI, which contain only specific parts of the original molecule can provide valuable information on the positional distribution of the label. The chemical formula of a fragment ion is usually applied to derive the correction matrix for accurate MID calculation. Hence, the correct assignment of chemical formulas to fragment ions is of crucial importance for correct MIDs. Moreover, the positional distribution of stable isotopes within a fragment ion is of high interest for stable isotope-assisted metabolomics techniques. For example, 13C-metabolic flux analyses (13C-MFA) are dependent on the exact knowledge of the number and position of retained carbon atoms of the unfragmented molecule. Fragment ions containing different carbon atoms are of special interest, since they can carry different flux information. However, the process of mass spectral fragmentation is complex, and identifying the substructures and chemical formulas for these fragment ions is nontrivial. For that reason, we developed an algorithm, based on a systematic bond cleavage, to determine chemical formulas and retained atoms for EI derived fragment ions. Here, we present the fragment formula calculator (FFC) algorithm that can calculate chemical formulas for fragment ions where the chemical bonding (e.g., Lewis structures) of the intact molecule is known. The proposed algorithm is able to cope with general molecular rearrangement reactions occurring during EI in GC/MS measurements. The FFC algorithm is able to integrate stable isotope labeling experiments into the analysis and can automatically exclude candidate formulas that do not fit the observed labeling patterns.1 We applied the FFC algorithm to create a fragment ion repository that contains the chemical formulas and retained carbon atoms of a wide range of trimethylsilyl and tert-butyldimethylsilyl derivatized compounds. In total, we report the chemical formulas and backbone carbon compositions for 160 fragment ions of 43 alkylsilyl-derivatives of primary metabolites. Finally, we implemented the FFC algorithm in an easy-to-use graphical user interface and made it publicly available at http://www.ffc.lu. [less ▲]

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See detailIsotope Cluster-Based Compound Matching in Gas Chromatography/ Mass Spectrometry for Non-Targeted Metabolomics
Wegner, André UL; Sapcariu, Sean UL; Weindl, Daniel UL et al

in Analytical Chemistry (2013), 85(8), 4030-4037

Gas chromatography coupled to mass spectrometry (GC/MS) has emerged as a powerful tool in metabolomics studies. A major bottleneck in current data analysis of GC/MS-based metabolomics studies is compound ... [more ▼]

Gas chromatography coupled to mass spectrometry (GC/MS) has emerged as a powerful tool in metabolomics studies. A major bottleneck in current data analysis of GC/MS-based metabolomics studies is compound matching and identification, as current methods generate high rates of false positive and false -negative identifications. This is especially true for data sets containing a high amount of noise. In this work, a novel spectral similarity measure based on the specific fragmentation patterns of electron impact mass spectra is proposed. An important aspect of these algorithmic methods is the handling of noisy data. The performance of the proposed method compared to the dot product, the current gold standard, was evaluated on a complex biological data set. The analysis results showed significant improvements of the proposed method in compound matching and chromatogram alignment compared to the dot product. [less ▲]

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See detailNontargeted Elucidation of Metabolic Pathways Using Stable-Isotope Tracers and Mass Spectrometry
Hiller, Karsten UL; Metallo, Christian M.; Kelleher, Joanne K et al

in Analytical Chemistry (2010)

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See detailMetaboliteDetector: comprehensive analysis tool for targeted and nontargeted GC/MS based metabolome analysis
Hiller, Karsten UL; Hangebrauk, Jasper; Jäger, Christian UL et al

in Analytical Chemistry (2009)

Detailed reference viewed: 412 (9 UL)