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Unsymmetrical dimethylhydrazine (UDMH) is a widely used rocket propellant. Entering the environment or being stored in uncontrolled conditions, UDMH easily forms an enormous variety (at least many dozens) of transformation products. Environmental pollution by UDMH and its transformation products is a major problem in many countries and across the Arctic region. Unfortunately, previous works often use only electron ionization mass spectrometry with a library search, or they consider only the molecular formula to propose the structures of new products. This is quite an unreliable approach. It was demonstrated that a newly proposed artificial intelligence-based workflow allows for the proposal of structures of UDMH transformation products with a greater degree of certainty. The presented free and open-source software with a convenient graphical user interface facilitates the non-target analysis of industrial samples. It has bundled machine learning models for the prediction of retention indices and mass spectra. A critical analysis of whether a combination of several methods of chromatography and mass spectrometry allows us to elucidate the structure of an unknown UDMH transformation product was provided. It was demonstrated that the use of gas chromatographic retention indices for two stationary phases (polar and non-polar) allows for the rejection of false candidates in many cases when only one retention index is not enough. The structures of five previously unknown UDMH transformation products were proposed, and four previously proposed structures were refined. [ABSTRACT FROM AUTHOR]

A technique of molecular statistical calculations, developed and improved with the active participation of workers at the Institute of Physical Chemistry and Electrochemistry, allows the accurate estimation of the chromatographic retention of analytes. The resulting version of molecular statistical method (with regard to conformational non-rigidity) is used to predict the values of alkylbenzene retention under conditions of gas adsorption chromatography. The accuracy of estimating the retention indices is compared to results from current machine learning approaches of predicting retention (for gas-liquid chromatography). The effectiveness of separating structural hydrocarbon isomers on different columns is also compared. [ABSTRACT FROM AUTHOR]

Mass spectrometry and chromatography are used to study the decomposition products of Teflon mixtures of the "Fluralite-4" brand with magnesium, tungsten, and titanium, activated by mechanochemistry. The temperature and energy parameters of water and carbon dioxide release are determined, volatile products of Teflon depolymerization are detected and identified, i.e., tetrafluoroethylene, trifluoromethylene, trifluoroethylene. It is shown that the introduction of metal mixtures in the composition significantly affects the decomposition processes of Teflon. [ABSTRACT FROM AUTHOR]

This paper discusses application of gas and liquid chromatography to studies of surface chemistry and various materials. Examples of studying adsorption processes from gas and liquid media with application of the chromatography technique are given. It is shown that the information on the structure of the material obtained using the chromatography technique allows predicting the regularities of chromatographic retention for molecules of different structures and various sorbents. The chromatography technique is frequently used in studies of nanomaterials and stable nanoparticles. It is shown that the chemical properties of surfaces modified by nanoparticles can be advantageously used in gas and liquid chromatography techniques. Much attention is given to molecular statistical calculations of adsorption on carbon sorbents in gas and liquid chromatography. The possibilities of the technique regarding prediction of retention of various sorbates and specification of structural parameters of molecules are demonstrated. Methodological and preparative aspects of a new area, micellar chromatography of nanoparticles, are considered. Options of liquid chromatography for separation, including preparative separation, identification, and classification, are shown. [ABSTRACT FROM AUTHOR]

Prediction of gas chromatographic retention indices based on compound structure is an important task for analytical chemistry. The predicted retention indices can be used as a reference in a mass spectrometry library search despite the fact that their accuracy is worse in comparison with the experimental reference ones. In the last few years, deep learning was applied for this task. The use of deep learning drastically improved the accuracy of retention index prediction for non-polar stationary phases. In this work, we demonstrate for the first time the use of deep learning for retention index prediction on polar (e.g., polyethylene glycol, DB-WAX) and mid-polar (e.g., DB-624, DB-210, DB-1701, OV-17) stationary phases. The achieved accuracy lies in the range of 16–50 in terms of the mean absolute error for several stationary phases and test data sets. We also demonstrate that our approach can be directly applied to the prediction of the second dimension retention times (GC × GC) if a large enough data set is available. The achieved accuracy is considerably better compared with the previous results obtained using linear quantitative structure-retention relationships and ACD ChromGenius software. The source code and pre-trained models are available online. [ABSTRACT FROM AUTHOR]

• Deep learning was applied to prediction of gas chromatographic retention indices. • Huge retention data sets are considered. • The developed model outperforms existing retention prediction models. • Median percentage error <2.2% for non-polar (polysiloxanes) stationary phases. • Usability of the model for mass spectral identification is demonstrated. A deep convolutional neural network was used for the estimation of gas chromatographic retention indices on non-polar (polydimethylsiloxane and polydimethyl(5%-phenyl) siloxane) stationary phases. The neural network can be used for candidate ranking while searching a mass spectral database. A linear representation (SMILES notation) of the molecule structure was used as an input for the model. The input line was converted to a one-hot matrix and then directly processed by the neural network. The calculation of any common molecular descriptors is avoided, following the modern tendency in machine learning: to allow the neural network to find the most preferable features by itself instead of using hard-coded features. The model has two 1D-convolutional layers with 120 neurons each followed by a pooling layer and a fully-connected layer with 200 hidden neurons. The model was compared with state-of-the-art models for prediction of gas chromatographic indices based on molecular descriptors and on functional groups contributions. On different data sets better accuracy is shown together with greater versatility. The applicability to diverse sets of flavors and fragrances, essential oils, metabolites is shown. The possibility of using the model for improvement of mass spectral identification (without reference retention index) is demonstrated. The median absolute error and the median percentage error are in the range of 17.3 (0.93%) to 38.1 (2.15%) depending on used test data set. Ready-to-use neural network parameters are provided. [ABSTRACT FROM AUTHOR]

Unsymmetrical dimethylhydrazine (UDMH) is a toxic and environmentally hostile compound that was massively introduced to the environment during previous decades due to its use in the space and rocket industry. The compound forms multiple transformation products, and many of them are as dangerous as UDMH or even more dangerous. The danger includes, but is not limited to, acute toxicity, chronic health hazards, carcinogenicity, and environmental damage. UDMH transformation products are poorly investigated. In this work, the mixture formed by long storage of the waste that contained UDMH was studied. Even a preliminary screening of such a mixture is a complex task. It consists of dozens of compounds, and most of them are missing in chemical and spectral databases. The complete preparative separation of such a mixture is very laborious. We applied several methods of gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry, and several machine learning and chemoinformatics methods to make a preliminary but informative screening of the mixture. Machine learning allowed predicting retention indices and mass spectra of candidate structures. The combination of various ion sources and a comparison of the observed with the predicted spectra and retention was used to propose confident structures for 24 compounds. It was demonstrated that neither high-resolution mass spectrometry nor mass spectral library matching is enough to elucidate the structures of unknown UDMH transformation products. At the same time, the use of machine learning and a combination of methods significantly improves the identification power. Finally, machine learning was applied to estimate the acute toxicity of the discovered compounds. It was shown that many of them are comparable to or even more toxic than UDMH itself. Such an extremely wide and still underestimated variety of easily formed derivatives of UDMH can lead to a significant underestimation of the potential hazard of this compound. [Display omitted] • The complex mixture of UDMH transformation products was studied. • Gas and liquid chromatography-mass spectrometry were used. • Machine learning methods contribute greatly to the mixture analysis. • Structures of 24 mixture components were determined. • The mixture contains many compounds as toxic as UDMH itself. [ABSTRACT FROM AUTHOR]

The most successful method for pyrolysis liquids analysis is comprehensive two-dimensional gas chromatography. Columns with a stationary liquid phase are used for this purpose. However, when is necessary to analyze a gas phase containing C 3 –C 5 hydrocarbons over a liquid pyrolysis product, the use of columns with a liquid phase in CG*CG will not result to separation of light hydrocarbons. In this case, it is necessary to use PLOT columns with a porous layer of sorbents of various nature. Today this approach with two PLOT columns in GC*GC is not described, as well as its use for the analysis of light hydrocarbons resulting from pyrolysis. This paper describes an application of two PLOT columns in GC*GC mode. This paper describes an application of two PLOT columns in GC*GC mode. The next columns of different nature that have different selectivity were used: Rt-Q-BOND, Rt-S-BOND, Rt-U-BOND (columns based on divinylbenzene styrene copolymer), column with sorbent poly- (1-trimethylsilyl-1-propyne) (PTMSP) and an Agilent GASPRO silica column. The most suitable pair of the columns was determined by finding of their orthogonality. The numerical orthogonality data was found by studying of the correlation coefficients between compounds retention time on the first and second columns. It is shown that the best combination of columns are PTMSP - GASPRO and Rt-Q-BOND - GASPRO, however, the first combination of columns allows separation at the same temperature conditions about twice as fast as the second. Examples of the separation of С 3 -С 8 hydrocarbons in the gas phase over pyrolysis mixtures of different origin are given. • Pyrolysis of used tires and plastic waste. • Analysis of light hydrocarbons in pyrolysis products by GC * GC with PLOT columns. • Optimization of chromatographic separation: the choice of the best columns pair. [ABSTRACT FROM AUTHOR]