Calculations of the Thermodynamic Characteristics and Physicochemical Properties of Symmetric and Asymmetric Isomeric Compounds for Identification in Chromatography-Mass Spectrometry

Abstract

A combination of theoretical and experimental approaches was applied to determine the chromatographic rules of isomeric compounds’ behavior for preliminary identification. In gas chromatography-mass spectrometry (GC-MS), identification is performed by spectra matching, however, difficulties arise with isomeric compounds, which cannot be distinguished from each other without additional information. The thermodynamic characteristics of the adsorption of symmetric and asymmetric isomers of сhlorophenylphenols, dimethoxybiphenyls, tri- and tetrachlorobiphenyls were determined using molecular statistical calculations. By-products in the chlorination of 4-hydroxybiphenyl were identified: 4-hydroxy-2,3′- and 3,2′-dichlorobiphenyls, 4-hydroxy-3,5,2′- and 2,3,6-trichlorobiphenyls. A developed theoretical approach was applied to predict the retention order of tri- and tetra-chlorobiphenyls. The GC-MS data and molecular statistical calculations made it possible to determine the main products of methoxybenzene dimerization as well as identify impurities. Thermodynamic parameters were received to describe the unusual retention behavior of epimers in reversed-phase high-performance liquid chromatography. Molecular descriptors were calculated to determine correlation with retention of both structural isomers and epimers. Descriptor combining surface area and partial charge information turned out to be useful in evaluating retention order for isomers.

Computed Mass-Fragmentation Energy Profiles of Some Acetalized Monosaccharides for Identification in Mass Spectrometry

“…The pairs of enantiomers could not be discriminated using this technique because they have identical profiles. Given these aspects and the good results that have been presented in similar studies [11][12][13][14][15][16][17], it is expected that the correlation of the profiles with the mass spectra of the chemical standards is only maximum for the truly positive results. Optimizing the experimental impact energy and the correlation relationship could also improve the analysis.…”

“…Although originally designed as a separation method, chromatography was later perfected to become a formidable analytical method using chemical standards. Recent studies have shown that the qualitative analysis of some symmetric and asymmetric isomers can also be performed by establishing the elution order, based on the thermodynamic characteristics of adsorption, using molecular statistical calculations [12]. Some techniques that use the quantitative structure-fragmentation relationship (QSFR) can filter the candidate structures using the reverse ordering of the calculated formation enthalpies (∆ f H) of their primary ions, together with the corresponding experimental ionic currents obtained by mass spectrometry.…”

Mass–Energy Profiles Obtained by Quantum Chemical Computing Applied in Mass Spectrometry: A Case Study with Identification of a Group of Acetalized Monosaccharide Isomers

“…The coupling of chromatography with mass spectrometry has offered the possibility of analyzing complex mixtures of analytes [5]. In addition to the classical use of standards, they use new variants of data processing and interpretation, which have been effectively translated to computational molecular simulation approaches [6][7][8].…”

“…Furthermore, the fulfillment of each of these objectives has an original conception and/or route. The optimization of the technique was achieved by group validation of analytes, a variant frequently used in chromatography because it can simultaneously cover a variety of structures [6,8]. The optimization used four independent variables: the quantum chemical (QC) method, the descriptor of calculated energy, the impact energy (IE) of electrons, and the descriptor of experimental energy.…”