The Experts below are selected from a list of 4809873 Experts worldwide ranked by ideXlab platform

Renato Zenobi - One of the best experts on this subject based on the ideXlab platform.

  • minimizing ion competition boosts volatile metabolome coverage by secondary electrospray ionization orbitrap mass spectrometry
    2021
    Co-Authors: Jiayi Lan, Jerome Kaeslin, Giorgia Greter, Renato Zenobi
    Abstract:

    Abstract Secondary electrospray ionization high-resolution mass spectrometry (SESI-HRMS) is an emerging technique for the detection of volatile metabolites. However, sensitivity and reproducibility of SESI-HRMS have limited its applications in untargeted metabolomics profiling. Ion suppression in the SESI source has been considered to be the main cause. Here, we show that besides ion suppression, ion competition in the C-trap of Orbitrap instruments is another important factor that influences sensitivity and reproducibility of SESI-MS. Instead of acquiring the full Mass-to-Charge Ratio (m/z) range, acquisition of consecutive m/z windows to minimize the ion competition effect allows the detection of more features. m/z window ranges are optimized to fill the C-trap either with an equal number of features or an equal cumulative intensity per window. Considering a balance between maximizing scanning speed and minimizing ion competition, splitting the m/z = 50-500 range into 4 windows is selected for measuring human breath and bacterial culture samples on SESI-Orbitrap MS, corresponding to a duty cycle of 2.3 s at a resolution of 140’000. In a small cohort of human subjects, the proposed splitting into 4 windows allows three times more features to be detected compared to the classical full m/z range method.

  • minimizing ion competition boosts volatile metabolome analysis by secondary electrospray ionization orbitrap mass spectrometry
    2020
    Co-Authors: Jerome Kaeslin, Jiayi Lan, Renato Zenobi
    Abstract:

    Secondary electrospray ionization high-resolution mass spectrometry (SESI-HRMS) is an emerging technique for the detection of volatile metabolites. However, sensitivity and reproducibility of SESI-HRMS have limited its applications in untargeted metabolomics profiling. Ion suppression in the SESI source has been considered to be the main cause. Here, we show that besides ion suppression, ion competition in the C-trap of Orbitrap instruments is another important factor that influences sensitivity and reproducibility of SESI-MS. Instead of acquiring the full Mass-to-Charge Ratio (m/z) range, acquisition of consecutive m/z windows to minimize the ion competition effect allows the detection of more features. m=z window ranges are optimized to fill the C-trap either with an equal number of features or an equal cumulative intensity per window. Considering a balance between maximizing scanning speed and minimizing ion competition, splitting the m/z = 50-500 range into 4 windows is selected for measuring human breath and bacterial culture samples on SESI-Orbitrap MS, corresponding to a duty cycle of 2:3 s at a resolution of 140000. In a small cohort of human subjects, the proposed splitting into 4 windows allows three times more features to be detected compared to the classical full m/z range method.

Peter Juhasz - One of the best experts on this subject based on the ideXlab platform.

  • resolution and mass accuracy in matrix assisted laser desorption ionization time of flight
    1998
    Co-Authors: Marvin L Vestal, Peter Juhasz
    Abstract:

    A mathematical model of time-of-flight mass analyzers employing uniform electric fields is presented that allows “exact” calculations of flight times as functions of Mass-to-Charge Ratio, initial velocity and position, applied voltages, and instrument geometry. An “approximate” equation based on a series expansion of the “exact” result is derived which allows focusing conditions and limits on resolution to be determined for different instrument geometries and operating conditions. The fundamental theory is applied to predicting resolution and mass accuracy in matrix-assisted laser desorption ionization-time of flight. In this case higher order velocity focusing can provide excellent correction for the initial velocity distribution of a selected Mass-to-Charge Ratio, but the focusing is Mass-to-Charge Ratio dependent. There is generally a trade-off between ultimate resolution at a particular Mass-to-Charge Ratio and resolution and mass accuracy over a broad mass range. In most practical applications the latter is more important. Calculations are compared with experimental results for a particular analyzer geometry, both at theoretical optimum velocity focus and at operating conditions where ultimate resolution is sacrificed for a broader range of relatively high resolution and better mass accuracy.

Jiayi Lan - One of the best experts on this subject based on the ideXlab platform.

  • minimizing ion competition boosts volatile metabolome coverage by secondary electrospray ionization orbitrap mass spectrometry
    2021
    Co-Authors: Jiayi Lan, Jerome Kaeslin, Giorgia Greter, Renato Zenobi
    Abstract:

    Abstract Secondary electrospray ionization high-resolution mass spectrometry (SESI-HRMS) is an emerging technique for the detection of volatile metabolites. However, sensitivity and reproducibility of SESI-HRMS have limited its applications in untargeted metabolomics profiling. Ion suppression in the SESI source has been considered to be the main cause. Here, we show that besides ion suppression, ion competition in the C-trap of Orbitrap instruments is another important factor that influences sensitivity and reproducibility of SESI-MS. Instead of acquiring the full Mass-to-Charge Ratio (m/z) range, acquisition of consecutive m/z windows to minimize the ion competition effect allows the detection of more features. m/z window ranges are optimized to fill the C-trap either with an equal number of features or an equal cumulative intensity per window. Considering a balance between maximizing scanning speed and minimizing ion competition, splitting the m/z = 50-500 range into 4 windows is selected for measuring human breath and bacterial culture samples on SESI-Orbitrap MS, corresponding to a duty cycle of 2.3 s at a resolution of 140’000. In a small cohort of human subjects, the proposed splitting into 4 windows allows three times more features to be detected compared to the classical full m/z range method.

  • minimizing ion competition boosts volatile metabolome analysis by secondary electrospray ionization orbitrap mass spectrometry
    2020
    Co-Authors: Jerome Kaeslin, Jiayi Lan, Renato Zenobi
    Abstract:

    Secondary electrospray ionization high-resolution mass spectrometry (SESI-HRMS) is an emerging technique for the detection of volatile metabolites. However, sensitivity and reproducibility of SESI-HRMS have limited its applications in untargeted metabolomics profiling. Ion suppression in the SESI source has been considered to be the main cause. Here, we show that besides ion suppression, ion competition in the C-trap of Orbitrap instruments is another important factor that influences sensitivity and reproducibility of SESI-MS. Instead of acquiring the full Mass-to-Charge Ratio (m/z) range, acquisition of consecutive m/z windows to minimize the ion competition effect allows the detection of more features. m=z window ranges are optimized to fill the C-trap either with an equal number of features or an equal cumulative intensity per window. Considering a balance between maximizing scanning speed and minimizing ion competition, splitting the m/z = 50-500 range into 4 windows is selected for measuring human breath and bacterial culture samples on SESI-Orbitrap MS, corresponding to a duty cycle of 2:3 s at a resolution of 140000. In a small cohort of human subjects, the proposed splitting into 4 windows allows three times more features to be detected compared to the classical full m/z range method.

Frank Vanhaecke - One of the best experts on this subject based on the ideXlab platform.

  • laser ablation tandem icp mass spectrometry la icp ms ms for direct sr isotopic analysis of solid samples with high rb sr Ratios
    2016
    Co-Authors: Eduardo Boleafernandez, Marti Resano, Stijn Van Malderen, Lieve Balcaen, Frank Vanhaecke
    Abstract:

    The combination of laser ablation and tandem ICP-mass spectrometry (LA-ICP-MS/MS) allows for successful Sr isotopic analysis of solid samples with high Rb/Sr Ratios. Isobaric overlap at a Mass-to-Charge Ratio of 87 (87Sr–87Rb) is overcome via chemical resolution. By using CH3F/He (10% CH3F in He), in an octopole collision-reaction cell, Sr+ ions are converted into the corresponding SrF+ reaction product ions, while Rb+ ions show no reactivity towards this gas mixture. Two sample introduction setups, leading to “dry” and “wet” plasma conditions, respectively, were evaluated and the figures of merit are documented in detail. The 87Sr/86Sr isotope Ratio results were corrected for instrumental mass discrimination using a double correction approach – internal correction using the Russell law, followed by external correction in a sample–standard bracketing (SSB) approach. NIST SRM 610 was applied as an external standard for mass bias correction; no closer matrix-matching was required for the sample types investigated. Under “wet” plasma conditions, accurate and precise (0.02–0.05% RSD) 87Sr/86Sr isotope Ratio results were obtained for 7 glass-type geological reference materials.

  • tandem icp mass spectrometry for sr isotopic analysis without prior rb sr sepaRation
    2016
    Co-Authors: Eduardo Oleafernandez, Lieve Alcae, Marti Resano, Frank Vanhaecke
    Abstract:

    The use of a mixture of 10% of CH3F and 90% of He as a reaction gas in tandem ICP-mass spectrometry (ICP-MS/MS) enables the accurate determination of the 87Sr/86Sr isotope Ratio in geological materials, provided that mass discrimination is corrected for by using a combination of internal (Russell law, assuming a constant 88Sr/86Sr isotope Ratio) and external correction (using the isotopic reference material NIST SRM 987 SrCO3) in a sample-standard bracketing approach. No prior Rb/Sr sepaRation is required as the isobaric overlap at a Mass-to-Charge Ratio of 87 is avoided by monitoring SrF+ reaction product ions instead of Sr+ ions. Rb shows no reactivity towards CH3F. The double mass selection (MS/MS mode) prevents both spectral overlap from atomic ions at the Mass-to-Charge Ratios of SrF+ reaction product ions and a measurable effect from the matrix on the 87Sr/86Sr result. This aspect is critical, as it enables accurate results to be obtained without the need for using a matrix-matched standard to correct for mass discrimination, in contrast to previous work with a quadrupole ICP-MS instrument with a CH3F/Ne-pressurized cell, in which the use of a matrix-matched standard was compulsory. The precision attainable – 0.05% RSD external precision – suffices for making the newly developed method useful in a variety of applications.

Carolyn J. Cassady - One of the best experts on this subject based on the ideXlab platform.

  • negative ion matrix assisted laser desorption ionization time of flight post source decay calibRation by using fibrinopeptide b
    1998
    Co-Authors: Jaran Jainhuknan, Carolyn J. Cassady
    Abstract:

    Fibrinopeptide B (Mr 1552.58) was employed as a calibRation compound for matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) post-source decay (PSD) fragment ion analysis in the negative mode. Experiments were performed by using both continuous and delayed extraction, with the maximum reflectron voltages being 30 and 21 kV, respectively. For comparison, a common positive ion PSD calibrant, ACTH(18–39) (Mr 2466.7), was also employed with positive ion calibRation constants being applied to negative ion spectra. Using fibrinopeptide B as the calibrant, the negative ion PSD results for angiotensin II (Mr 1046.2), renin substrate tetradecapeptide (horse) (Mr 1759.0), and the custom-synthesized peptide (K2G4)2 (Mr 987.1) showed a factor of 1.5–2 improvement in absolute mass accuracy. Typical absolute Mass-to-Charge Ratio accuracies were within ±1 Thomson and were achieved even when the peptide being analyzed was more massive than fibrinopeptide B. In addition, both calibrants showed increased accuracy when experiments were conducted in the delayed extraction mode. Other advantages of using fibrinopeptide B are its moderate cost and the ability to perform calibRation and sample analysis for negative ion PSD under the same instrumental conditions.