Elemental Composition Determinations Using the Abundant Isotope March 7, 2020 Mass Spectrometry (MS), MS Peer-Reviewed Articles 0 Abstract Elemental compositions are commonly determined from the exact m/z of the monoisotopic peak, which is often the lightest isotope. However, the lightest isotope peak is often weak or absent and the monoisotopic peak can be difficult to identify for organometallics, polyhalogenated compounds, or large molecules. An alternative approach using the abundant isotope for elemental composition determinations is presented here. For more information: https://link.springer.com/article/10.1007/s13361-019-02203-9?wt_mc=Internal.Event.1.SEM.ArticleAuthorAssignedToIssue&utm_source=ArticleAuthorAssignedToIssue&utm_medium=email&utm_content=AA_en_06082018&ArticleAuthorAssignedToIssue_20190627 Related Articles Accurate Isotope Data is Essential for Determining Elemental Compositions Elemental compositions are commonly determined from high-resolution mass spectra and accurate mass measurements. Given a measured mass (m/z) and a range of elements that can be present, software calculates the exact mass for each combination of elements and reports all elemental combinations that match the measured mass within a specified error tolerance. Improving the mass accuracy reduces the number of elemental compositions, but mass accuracy alone may not be sufficient to determine the correct elemental composition for an unknown sample. JEOL AccuTOF™ mass spectrometers (the AccuTOF™-DART®, the AccuTOF™-GCX and the AccuTOF™-GCX Plus) are capable of accurate isotope measurements that can be used to determine elemental compositions from high-resolution mass spectra. Matching the measured abundances and exact masses for isotope peaks can be more effective than mass accuracy alone. Automated Exact Mass Measurements and Elemental Composition Determinations The JEOL AccuTOF™ LC/MS system offers easy exact-mass measurements and elemental composition determinations. A robust design and stable time-of-flight mass analyzer are combined with a detection system that provides high sensitivity and high dynamic range. Unlike other API/TOF mass spectrometer systems, the AccuTOF™ provides excellent linearity and mass accuracy over a wide range of analyte concentrations. To demonstrate the potential of the AccuTOF™ for automated exact mass measurements, a variety of small-molecule drug samples were measured by using a macro that allows the user to submit samples for unattended elemental composition determinations. Samples were introduced by using the LC autosampler. The macro applied an automatic drift (“lock mass”) correction to the reserpine reference standard and printed out elemental compositions for user-specified elemental limits. The results show high accuracy and stability regardless of sample concentration. Elemental Compositions from Exact Mass Measurements and Accurate Isotopic Abundances Exact masses have been used for decades to calculate elemental compositions for known and unknown molecules. The traditional approach calculates all possible combinations of user-specified atoms that fall within a given error tolerance of a measured mass. The number of possible combinations increases dramatically with increasing mass and as more atoms are included in the search set. In many cases, it is not possible to determine a unique composition based on mass alone. A common source of error in measuring isotopic abundances with scanning mass spectrometers is related to fluctuations in ion current during measurement. The AccuTOF family of mass spectrometers overcomes this problem by analyzing all of the isotopes formed at the same instant. Combined with a high-dynamic-range detector, this provides highly accurate isotopic abundances. It has been shown that accurately measured isotopic abundances can be combined with measured exact masses to dramatically reduce the number of possible elemental compositions for an unknown. It is often possible to deduce a unique elemental composition, facilitating the identification of unknown substances. “Remainders of KM” plot for polymers using msRepeatFinder: compositional mapping over a broad mass range Mass Spectrometry (MS) with soft ionization such as matrix-assisted laser desorption ionization (MALDI) allows the compositional analysis of polymers (repeating units, chain terminations) of low dispersity. Combining a size exclusion chromatography (SEC) fractionation with a high-resolution MALDI SpiralTOF™ MS analysis enables the evaluation of the composition of polydisperse polymeric samples over a broad mass range (high-resolution/high-accuracy mass measurements in the low mass range < 4 kDa, isotopic resolution in higher mass range < 30kDa). However, as the resolution gets higher, more peaks are detected in the mass spectrum for each fraction, making the interpretation of the mass spectral data the rate-limiting step for the whole analytical procedure. In this work, a “remainders of Kendrick mass” (RKM) analysis is used as a rapid post-acquisition data processing tool that uses visual maps from combined low/high-accuracy and low/high mass range data. MS Elemental Composition Calculations and Their Interpretation Accurate mass measurements are frequently used to determine the elemental composition for molecular and fragment ions. These measurements are normally obtained by acquiring a high resolution mass spectrum so that the masses are measured for a single species and not measured for unresolved or partially resolved peaks. Thermal-decomposition Process Analysis of Sodium Formate Using TG-MS Thermogravimetry (TG) is used to measure weight changes of samples under programmed heat conditions. A system combining thermogravimetry/differential thermal analysis (TG/DTA) with mass spectrometry (MS) can be used for both qualitative and quantitative analysis of gases evolved from the TG furnace into the mass spectrometer. In this application note, we show qualitative analysis of the thermal-decomposition process for sodium formate using the “STA2500 Regulus” TG system (NETZSCH) and the gas chromatography–quadrupole mass spectrometry (GC/QMS) “JMS-Q1500GC” system (JEOL). Showing 0 Comment Comments are closed.