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Öğe Green chromatographic separation of coumarin and vanillins using subcritical water as the mobile phase(Oxford Univ Press İnc, 2016) Kayan, Berkant; Akay, Sema; Yang, YuPure water was used as the eluent for separation of coumarin, vanillin and ethyl vanillin at temperatures ranging from 100 to 200 degrees C using a homemade subcritical water chromatography (SBWC) system. Chromatographic separations were performed on five commercial columns including XTerra MS C18, XBridge C18, Zorbax RRHD Eclipse Plus, Zorbax SB-Phenyl and Zorbax SB-C18 columns. The retention time of all three solutes decreased with increasing water temperature. The shortest retention time among all acceptable separations, less than 4 min, was achieved on the Zorbax SB-C18 column at 200 degrees C. While separations on the XTerra MS C18 column resulted in fronting peaks and a degradation peak from ethyl vanillin on the Zorbax RRHD Eclipse Plus column was observed, all three other columns yielded reasonable separations under SBWC conditions. In addition to separation of the standard test mixture, separation of coumarin contained in a skincare cream sample was also carried out using SBWC.Öğe Investigation on the solubility of the antidepressant drug escitalopram in subcritical water(American Chemical Society, 2021) Akay, Sema; Kayan, Berkant; Yang, YuEscitalopram (ESC), the S-enantiomer of citalopram, is a selective serotonin reuptake inhibitor. Escitalopram is widely used to treat panic disorder, depression, obsessive compulsive disorder, and social anxiety disorder. The main goal of this present research is to determine the aqueous solubility of ESC at temperatures ranging from 298 to 473 K and a pressure of 5.0 MPa. ESC solubility increased significantly from 1.08 × 10-3 to 59.88 × 10-3 (mole fraction) when the temperature was raised from 298 to 473 K. This is a 55-fold enhancement. A mathematical model was developed based on our experimental solubility data. The model was used to successfully predict the solubility of ESC in subcritical water. Furthermore, experimental data were correlated using a modified Apelblat equation. The apparent thermodynamic analysis including apparent dissolution standard enthalpy (?solH) and apparent dissolution standard entropy (?solS) were calculated. Thermodynamic property calculations showed that the process is endothermic ?solH > 0, and the ?solS values were relatively high. Spectroscopic analyses revealed that ESC was stable in subcritical water at temperatures up to 473 K. The enhanced solubility of ESC in subcritical water enabled us to use high-temperature liquid chromatography to separate this antidepressant drug.Öğe Research of sulfadiazine using subcritical water and water plus alcohol mixtures as the solvent: Solubility and thermodynamic property(Elsevier, 2018) Akay, Sema; Kayan, Berkant; Du Cunbin; Wang, Jiang; Yang, YuSulfonamides are drugs extensively used for the treatment of infections caused by gram-positive and gram negative microorganisms, some fungi, and certain protozoa. They are also used in agriculture to prevent and treat diseases in livestock. Sulfadiazine is a member of the sulfonamide family. In this study, the solubility of sulfadiazine in pure subcritical water and water + alcohol mixtures has been measured using a homemade system at (298 to 403) K under a constant pressure of 5.1 MPa. Our results revealed that the solubility of sulfadiazine was enhanced with increasing temperature and higher percentage of ethanol or propanol in water. Modified Apelblat equation and CNIBS/R-K model were used to correlate and predict the solubility of sulfadiazine in pure subcritical water as well as in subcritical water + alcohol mixtures. The predicted solubility values are in good correlation with the experimental data. In addition, "Apparent thermodynamic analysis" was applied to calculate the dissolution enthalpy property of the solution process.Öğe Solubility and chromatographic separation of 5-fluorouracil under subcritical water conditions(American Chemical Society, 2017) Akay, Sema; Kayan, Berkant; Yang, YuThe drug 5-fluorouracil is used to treat several cancers including colon, esophageal, stomach, pancreatic, breast, and cervical cancer. In this study, the solubility of 5-fluorouracil in subcritical water was determined at temperatures ranging from 298 to 473 K under a constant pressure of 5.1 MPa. Our results show that the solubility of 5-fluorouracil is enhanced more than 12 -fold by increasing the temperature from 298 to 473 K. A new approximation model was developed to predict the solubility of 5-fluorouracil in subcritical water. Our predicted solubility values are comparable with the experimental ones. The modified Apelblat equation also yields good agreement with experimental values. Since our solubility study reveals that 5-fluorouracil has adequate solubility in subcritical water, the separation of 5-fluorouradl was conducted using subcritical water chromatography (SBWC) with water only mobile phase. Good chromatographic separation of 5-fluorouracil was achieved at temperatures of 348 to 473 K.Öğe Solubility and decomposition of organic compounds in subcritical water(MDPI, 2023) Yabalak, Erdal; Akay, Sema; Kayan, Berkant; Gizir, A. Murat; Yang, YuIn this article, studies on organic solubility and stability in subcritical water reported during the past 25 years have been reviewed. Data on the solubility and decomposition of organic compounds in subcritical water, a green solvent, are needed in environmental remediation, chemistry, chemical engineering, medicine, polymer, food, agriculture, and many other fields. For solubility studies, the experimental systems used to measure solubility, mathematical equations derived and applied for the modeling of the experimentally determined solubility data, and the correlation between the predicated and experimental data have been summarized and discussed. This paper also reviewed organic decomposition under subcritical water conditions. In general, the solubility of organics is significantly enhanced with increasing water temperature. Likewise, the percentage of organic decomposition also increases with higher temperature.Öğe Stability and extraction of vanillin and coumarin under subcritical water conditions(MDPI AG, 2020) Doctor, Ninad; Parker, Grayson; Vang, Katie; Smith, Melanie; Kayan, Berkant; Yang, YuIn order to facilitate the development of the green subcritical water chromatography technique for vanillin and coumarin, the stability of the compounds under subcritical water conditions was investigated in this work. In addition, their extraction from natural products was also studied. The stability experiments were carried out by heating the mixtures of vanillin and water or coumarin and water at temperatures ranging from 100 ?C to 250 ?C, while subcritical water extractions (SBWE) of both analytes from vanilla beans and whole tonka beans were conducted at 100 ?C to 200 ?C. Analyte quantification for both stability and extraction studies was carried out by HPLC. After heating for 60 min, vanillin was found to be stable in water at temperatures up to 250 ?C. While coumarin is also stable at lower temperatures such as 100 ?C and 150 ?C, it undergoes partial degradation after heating for 60 min at 200 ?C and higher. The results of this stability study support green subcritical water chromatographic separation and extraction of vanillin and coumarin at temperatures up to 150 ?C. The SBWE results revealed that the extraction efficiency of both analytes from vanilla beans and tonka beans is significantly improved with increasing temperature.Öğe Synthesis and evaluation of NA-PHEMAH polymer for use as a new stationary phase in high-temperature liquid chromatography(ELSEVIER SCIENCE BV, 2015) Akay, Sema; Odabaşı, Mehmet; Yang, Yu; Kayan, BerkantIn order to develop more stable packing materials for high-temperature liquid chromatography (HTLC), a new stationary phase, 1-naphthyl attached poly(2-hydroxyethylmethacrylate-N-methacryloyl-(L)-histidine-methyl-ester) (NA-PHEMAH) polymer was synthesized in this work. The NA-PHEMAH polymer particles with 2.0-2.1 mu m in diameter were then evaluated for use as a stationary phase in high-temperature liquid chromatography. Separation of vanillin, ethyl vanillin, coumarin, 6-methylcoumarin, and 7-methylcoumarin was achieved on this NA-PHEMAH column using HTLC at 125-200 degrees C with 2% or 5% methanol in the mobile phase. Successful separation of the test analytes was also obtained using subcritical water chromatography (SBWC) at 200 degrees C. Evaluation of the long-term stability of the NA-PHEMAH stationary phase revealed that the column was stable for over 500 h at 150 degrees C. These results demonstrate that the new NA-PHEMAH stationary phase is suitable for high-temperature liquid chromatography separations due to its excellent stability at high temperatures.
