The Power of Exact Mass Measurement: An Example of Unknown Compound Identification March 5, 2020 AccuTOF™ GC, Application Note, Mass Spectrometry (MS), Materials 0 Introduction Recently, JEOL introduced the AccuTOF-GC, an innovative GC/time-of-flight mass spectrometer (TOF MS) that is capable of both high data acquisition rates and easy exact mass measurements. The exact mass measurements can then be used to generate lists of possible elemental compositions, which is a powerful tool for identifying unknown compounds. Additionally, this information can be combined with the fragmentation information to help confirm the identity an unknown compound. In this work, the AccuTOF-GC system was used to identify an unknown compound in a liquid crystal extract. Experimental The system used for this work was the JEOL AccuTOF-GC TOF MS. Liquid crystal from a pocket calculator display was dissolved in hexane. Afterwards, the sample was injected onto a DB-5 GC column (0.18mm x 10m, 0.18μm film thickness). The oven temperature was held at 40°C for 1 min and then increased to 300°C at 50°C/min rate. The TOF MS was tuned to achieve a resolution of 5,000 (FWHM) at m/z 293 (Perfluorokerosene). 2,4,6-tris(trifluoromethyl)-1,3,5-triazine was used as an internal standard for the exact mass measurements in both EI and CI modes. The CI reagent gas was isobutane. The NIST mass spectral database (2002) was used for the EI spectrum searches. For full details: Attached files often contain the full content of the item you are viewing. Be sure and view any attachments. ZW Exact Mass Measurement.pdf 147.8 KB Related Articles LC/MS: Identification of Unknowns by Combining Exact Mass Measurement with the NIST 02 Mass Spectral Database Similarity Search Electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) tend to produce mass spectra with minimal fragmentation. Positive-ion mass spectra are dominated by protonated molecules and cation attachment, while negative-ion mass spectra usually show molecular anions or ions produced by hydride abstraction. However, by varying the potentials in the atmospheric pressure interface, collision-induced dissociation (CID) can produce mass spectra with extensive fragmentation. This is sometimes referred to as in-source CID. Because the ionization process and ion energies are different for ESI or APCI compared to electron ionization (EI), the fragmentation is often different from the EI mass spectra in common mass spectral databases. Furthermore, the fragmentation pattern can vary depending on in-source CID conditions. This leads one to question whether there is any value to searching an EI mass spectral database for ESI or APCI mass spectra. The NIST 02 Mass Spectral Search software provides functions for a structure similarity search. This search can be used to search the library for compounds with similar structures based on neutral losses, which is a more suitable method for searching ESI or APCI mass spectra against the library. Compounds that have mass spectra in the library database can often be identified from the search results. The similarity search can provide structural information about compounds that do not have mass spectra in the library by displaying the structures of similar compounds identified by the search. Non-targeted analysis of electronics waste by comprehensive two-dimensional gas chromatography combined with high-resolution mass spectrometry: Using accurate mass information and mass defect analysis to explore the data Comprehensive two-dimensional gas chromatography (GC×GC) and high-resolution mass spectrometry (HRMS) offer the best possible separation of their respective techniques. Recent commercialization of combined GC×GC–HRMS systems offers new possibilities for the analysis of complex mixtures. However, such experiments yield enormous data sets that require new informatics tools to facilitate the interpretation of the rich information content. This study reports on the analysis of dust obtained from an electronics recycling facility by using GC×GC in combination with a new high-resolution time-of-flight (TOF) mass spectrometer. New software tools for (non-traditional) Kendrick mass defect analysis were developed in this research and greatly aided in the identification of compounds containing chlorine and bromine, elements that feature in most persistent organic pollutants (POPs). In essence, the mass defect plot serves as a visual aid from which halogenated compounds are recognizable on the basis of their mass defect and isotope patterns. Mass chromatograms were generated based on specific ions identified in the plots as well as region of the plot predominantly occupied by halogenated contaminants. Tentative identification was aided by database searches, complementary electron-capture negative ionization experiments and elemental composition determinations from the exact mass data. These included known and emerging flame retardants, such as polybrominated diphenyl ethers (PBDEs), hexabromobenzene, tetrabromo bisphenol A and tris (1-chloro-2-propyl) phosphate (TCPP), as well as other legacy contaminants such as polychlorinated biphenyls (PCBs) and polychlorinated terphenyls (PCTs). 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. Analysis of Electronics Waste by GCxGC Combined with High-resolution Mass Spectrometry: Using Accurate Mass Information and Mass Defect Analysis to Explore the Data Comprehensive two-dimensional gas chromatography (GCxGC) in combination with high-resolution mass spectrometry (HRMS) is a powerful tool for the analysis of complex mixtures. However, new software tools are required to facilitate the interpretation of the rich information content in GCxGC/HRMS data sets. In this work, we analyzed a dust sample collected from an electronics recycling facility by using GCxGC in combination with a new high-resolution time-of-flight (TOF) mass spectrometer. Nontraditional Kendrick Mass Defect (KMD) plots were used to identify halogenated contaminants in an electronics waste sample. Database search results combined with elemental composition determinations from exact-mass data were used to identify (potential) persistent organic pollutants (POPs). The Relationship between Crystal Condition and Mass Resolving Power, Mass Accuracy The JMS-S3000 SpiralTOF™ has a unique 17 m flight path that offers the highest resolution MALDI-TOF MS system currently available. With an extended flight distance, the SpiralTOF reduces topographic effect of matrix crystal to a minimum and achieves highly reproducible mass resolving power and high mass accuracy with external mass calibration. In this work, we demonstrate the measurement of a polymer standard with 4 types of matrices that are typically used for MALDI polymer measurement by using the JEOL SpiralTOF system. Additionally, we looked at the crystal condition using the JEOL JSM-7600F thermal field emission scanning electron microscope (FE-SEM). Structural Characterization of Polymers by MALDI Spiral- TOF Mass Spectrometry Combined with Kendrick Mass Defect Analysis High-resolution mass spectrometry (HRMS) continues to play an important role in the compositional characterization of larger organic molecules. In the field of polymer characterization, however, the application of HRMS has made only slow progress because of lower compatibility between matrix-assisted laser desorption/ionization (MALDI) and ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICRMS). In this study, a newly developed type of MALDI high-resolution time-of-flight mass spectrometry (TOFMS) with a spiral ion trajectory (MALDI spiral-TOFMS) was applied to the structural and compositional characterization of polymers. To create a graphical distribution of polymer components on a two-dimensional plot converted from complex mass spectra, we adopted a slightly modified Kendrick mass defect (KMD) analysis based on accurate masses determined using spiral-TOFMS. By setting the Kendrick mass scale based on the mass of the repeating units of a given polymer, components with common repeat units lined up in the horizontal direction on the KMD plot, whereas those components with different structures were shifted vertically. This combination of MALDI spiral-TOFMS measurement and KMD analysis enabled the successful discrimination of the polymer components in a blend of poly(alkylene oxide)s, the compositional analysis of poly(ethylene oxide)/poly(propylene oxide) block copolymers, and profiling of the end-group distribution of poly(ε- caprolactone)s synthesized under different conditions. Showing 0 Comment Comments are closed.