The thermodynamic study of morpholinium 2-((4-(2-methoxyphenyl)-5-(pyridinyl)-4H-1,2,4-triazol-3-yl)thio)acetate and its technological impurities in hydrophilic chromatography
Aim. To study the dependence of the retention of morpholinium 2-((4-(2-methoxyphenyl)-5-(pyridinyl)-4H-1,2,4-triazol-3-yl)thio)acetate and its technological impurities on temperature, as well as determine the thermodynamic characteristics of the transfer from the mobile phase to the stationary phase using hydrophilic chromatography.
Results and discussion. The retention factors depending on the absolute temperature were determined in order to study the thermodynamic parameters of the transfer of analytes from the mobile phase to the stationary one. Based on the van ‘t Hoff equation a curve of lnk dependence on 1/T was constructed. The least squares method was used to create the linear dependence equation. The standard molar enthalpies, as well as the conditional standard entropy of the transfer from the mobile to the stationary phase of the test substances, namely morpholinium 2-((4-(2-methoxyphenyl)-5-(pyridinyl)-4H-1,2,4-triazol-3-yl)thio)acetate, pyridine-4-carbohydrazide, 2-isonicotinoyl-N-(2-methoxyphenyl)hydrazine-1-carbothioamide and 4-(2-methoxyphenyl)-5-(pyridinyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione were calculated. The negative enthalpy of the transfer for all substances shows that the substances are adsorbed on the surface of a silica gel with the release of heat. Therefore, the process of transition of a substance from the mobile phase to the stationary one prevails over the reverse process.
Experimental part. The Agilent 1260 Infinity liquid chromatography system consisting of a degasser, binary pump, autosampler, column thermostat, diode array detector was used for our experiments.
Conclusions. It has been found that all the compounds studied have a negative value of the transfer enthalpy, and it indicates the predominant transition of these analytes from the mobile phase to the stationary one. Conditional standard entropies of the analyte transfer from the mobile phase to the stationary phase have been calculated, and it has been proven that they significantly affect the transfer process.
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