Study of Chemical Exchange by 2D NMR June 12, 2020 Experimental Possibilities, Nuclear Magnetic Resonance (NMR) 0 The NMR signal of a spin reflects its local magnetic environment. If a spin due to chemical exchange samples two magnetically different states then its NMR signal would reflect both states. Its appearance on a NMR spectrum would be determined by the dynamics of the exchange event. In the case of chemical exchange that is slow on the NMR time scale, it is possible to observe two distinct signals for the same spin, one signal for each state under exchange. Presence of chemical exchange is often demonstrated with the exchange experiment (2D NOESY experiment). A exchange peak (cross peak) of the same sign can be observed between the two autopeaks (diagonal peaks) that represent the two states under exchange. Because the same results can be interpreted in a different way based on NOE, further evidence is desirable. For full details: Attached files often contain the full content of the item you are viewing. Be sure and view any attachments. Study of Chemical Exchange by 2D NMR.pdf 880.18 KB Related Articles Simultaneous determination of residual agricultural chemicals in food by GC-MS/MS - MSTips259 As "food safety" is recognized as an increasingly important issue on a global scale, many nations have their own regulations on residual agricultural chemicals in food. In Japan, the positive list system, which was enforced at the end of May 2006, stipulates a uniform standard of 10 ppb as a quantity that is considered safe for human health. Under the positive list system, more agricultural chemicals need to be examined, and as a result, techniques capable of accurately and collectively analyzing residual agricultural chemicals in food are in increasing demand. While mass spectrometry (MS) is known for its high detection sensitivity, MS/MS is becoming the mainstream of pesticide analysis for its superior sensitivity and selectivity. The JMS-TQ4000GC, JEOL’s latest GC-MS/MS system, has a unique ion storage/ejection mechanism within the MS/MS collision cell and incorporates new firmware to support MS/MS analysis with up to 36,000 transitions. In this work, we report the verified results for pesticide residues sensitivity in food using the JMS-TQ4000GC. Stability in quantitative analysis of residual agricultural chemicals in food by GC-MS/MS - MSTips262 As "food safety" is recognized as an increasingly important issue on a global scale, many nations have their own regulations on residual agricultural chemicals in food. In Japan, the positive list system, which was enforced at the end of May 2006, stipulates a uniform standard of 10 ppb as a quantity that is considered safe for human health. Under the positive list system, more agricultural chemicals need to be examined, and as a result, techniques capable of accurately and collectively analyzing residual agricultural chemicals in food are in increasing demand. While mass spectrometry (MS) is known for its high detection sensitivity, MS/MS is becoming the mainstream of pesticide analysis for its superior sensitivity and selectivity. The JMS-TQ4000GC, JEOL’s latest GC-MS/MS, has a unique ion storage/ejection mechanism within the MS/MS collision cell and incorporates new firmware to support MS/MS analysis with up to 36,000 transitions. In this work, we report the stability of 8 pesticides that were added to spinach extract. Molecular Characterization of Volatiles and Petrochemical Base Oils by Photo-Ionization GC×GC-TOF-MS The characterization of organic mixtures by comprehensive two-dimensional gas chromatography (GC×GC) coupled to electron impact (EI) ionization time-of-flight mass spectrometry (TOF-MS) allows the detection of thousands of compounds. However, owing to the exhaustive fragmentation following EI ionization, despite the use of mass spectral libraries, a majority of the compounds remains unidentified because of the lack of parent ion preservation. Thus, soft-ionization energies leading to organic compounds being ionized with limited or no fragmentation, retaining the molecular ion, has been of interest for many years. In this study, photoionization (PI) was evaluated as the ion source for GC×GC-TOF-MS measurements. First, capabilities and limitations of PI were tested using an authentic mixture of compounds of several chemical classes. Ionization energy exhibited by PI, equivalent to 10.8 eV, resulted in significant retention of molecular ion information; [M]+• for alkanes, ketones, FAMEs, aromatics, [M–H]+• for chloroalkanes, and [M–H2O]+• for alcohols. Second, considering the potential of PI for hydrocarbons, base oils, complex mixtures of saturated and unsaturated hydrocarbons blended for finished lubricant formulations, were extensively evaluated. Several chemical classes of hydrocarbons were positively identified including a large number of isomeric compounds, both aliphatics and cyclics. Interestingly, branched-alkanes were ionized with lower excess internal energy, not only retaining the molecular ions but also exhibiting unique fragmentation patterns. The results presented herein offer a unique perspective into the detailed molecular characterization of base oils. Such unprecedented identification power of PI coupled with GC×GC-TOF-MS is the first report covering volatiles to low-volatile organic mixtures. Chemical Analysis of Fingerprints Fingerprints contain a great deal of chemical information that is not often exploited for forensic analysis. DART can detect and identify the chemical components of fingerprints, often providing information about what substances a subject has been handling. Detecting the color chemicals in autumn leaves by using The Ambient Ionization Toolbox™ Some of the characteristic compounds that are responsible for the bright colors of autumn leaves are readily detected by using various ambient ionization methods with the AccuTOF-DART mass spectrometer system. Chemical Reaction Monitoring with the AccuTOF-DART™ Mass Spectrometer DART provides a convenient means for monitoring the progress of chemical reactions. Reactants, intermediates, products and byproducts can be detected by simply dipping a glass rod into the reaction pot and then placing the rod in front of the DART ion source. The AccuTOF's ability to measure accurate masses and isotopic abundances makes it possible to confirm or identify the elemental compositions of peaks in the mass spectra. Here we show the use of AccuTOF-DART to monitor the acetylation of 1,2-hexanediol as a function of time. Showing 0 Comment Comments are closed.