Comprehensive quantum chemical and mass spectrometric analysis of the McLafferty rearrangement of methyl valerate.

The McLafferty rearrangement (McLR) of the methyl valerate molecular ion has been comprehensively studied from the standpoints of the timescale for the keto-enol transformation and the change of the configuration of intermediates and transition state (TS), using mass spectrometry with electron ionization, strong-field tunnel ionization and collision-induced dissociation methods, and the global reaction route mapping (GRRM) program with quantum chemical calculations (QCCs). The timescales estimated from mass spectrometric results suggested that the McLR starts at 100 fs after ionization and is completed at least within 100 ns in the ion source. Whereas the timescales are consistent with a stepwise mechanism of fast (100 fs) and slow (10 ps) steps presented by Stamm , the QCCs put forth the possibility that an unanticipated, rapid, concerted process may be involved in completing the McLR reaction.

Quantum Chemical Analysis of Molecular and Fragment Ions Produced by Field Ionization of Methyl Stearate.

The formation of molecular and fragment ions observed in the field ionization mass spectrum of methyl stearate has been analyzed on the basis of quantum chemical calculations including time-dependent density functional theory (TDDFT) and natural bond orbital (NBO) analysis. The TDDFT calculations suggest that methyl stearate is ionized via two processes, namely a 7.43 eV excitation and a tunneling effect, while the high electric field of 10 V/m enables analyte molecules to ionize at an effective 6 eV lower than the 9.

Construction of a Mass Spectrum Library Containing Predicted Electron Ionization Mass Spectra Prepared Using a Machine Learning Model and the Development of an Efficient Search Method.

Electron ionization (EI) mass spectrum library searching is usually performed to identify a compound in gas chromatography/mass spectrometry. However, compounds whose EI mass spectra are registered in the library are still limited compared to the popular compound databases. This means that there are compounds that cannot be identified by conventional library searching but also may result in false positives.

Integrated data analysis making use of the total information from gas chromatography and high-resolution time-of-flight mass spectrometry to identify qualitative differences between two whisky samples.

Rationale: Analysis of complex mixtures with gas chromatography coupled with high-resolution time-of-flight mass spectrometry (GC/HRTOFMS) can produce a large amount of data. A new software program was recently reported that integrates all of the available mass spectrometric information from GC/HRTOFMS analysis into a concise report. New capabilities have now been added to the software to incorporate retention index data and to identify differences between two samples.

Integrated qualitative analysis of polymer sample by pyrolysis-gas chromatography combined with high-resolution mass spectrometry: Using accurate mass measurement results from both electron ionization and soft ionization.

Rationale: Gas chromatography/mass spectrometry (GC/MS) is a powerful analytical tool used to separate and then identify volatile compounds through library database searches. However, as not all compounds are registered in these databases, it is not uncommon to detect unregistered components. Therefore, new analytical techniques were developed that utilize methods of identification beyond database searches alone.

Direct analysis in real time high resolution mass spectrometry as a tool for rapid characterization of mind-altering plant materials and revelation of supplement adulteration--The case of Kanna.

We demonstrate the utility of direct analysis in real time ionization coupled with high resolution time-of-flight mass spectrometry (DART-HRTOFMS) in revealing the adulteration of commercially available Sceletium tortuosum, a mind-altering plant-based drug commonly known as Kanna. Accurate masses consistent with alkaloids previously isolated from S. tortuosum plant material enabled identification of the products as Kanna, and in-source collision-induced dissociation (CID) confirmed the presence of one of these alkaloids, hordenine, while simultaneously revealing the presence of an adulterant.

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.

High-energy collision-induced dissociation by MALDI TOF/TOF causes charge-remote fragmentation of steroid sulfates.

A method for structural elucidation of biomolecules dating to the 1980s utilized high-energy collisions (~10 keV, laboratory frame) that induced charge-remote fragmentations (CRF), a class of fragmentations particularly informative for lipids, steroids, surfactants, and peptides. Unfortunately, the capability for high-energy activation has largely disappeared with the demise of magnetic sector instruments. With the latest designs of tandem time-of-flight mass spectrometers (TOF/TOF), however, this capability is now being restored to coincide with the renewed interest in metabolites and lipids, including steroid-sulfates and other steroid metabolites.

Modified MALDI MS fatty acid profiling for bacterial identification.

Bacterial fatty acid profiling is a well-established technique for bacterial identification. Ten bacteria were analyzed using both positive- and negative-ion modes with a modified matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) approach using CaO as a matrix replacement (metal oxide laser ionization MS (MOLI MS)). The results show that reproducible lipid cleavage similar to thermal in situ tetramethyl ammonium hydroxide saponification/derivatization had occurred.

Quantification of polychlorinated dibenzo-p-dioxins and dibenzofurans by direct injection of sample extract into the comprehensive multidimensional gas chromatograph/high-resolution time-of-flight mass spectrometer.

Polychlorinated dibenzo-p-dioxins and dibenzofurans in crude extracts of fly ash and flue gas from municipal waste incinerators were quantified using a comprehensive multidimensional gas chromatograph (GC x GC) coupled to a high-resolution time-of-flight mass spectrometer (HR-TOFMS). For identification and quantification, we developed our own program to prepare 3D chromatograms of selected mass numbers from the data of the GC x GC/HR-TOFMS. Isolation of all congeners with a TCDD toxic equivalency factor from the other isomers by only one injection was confirmed.