Chemistry / Kimya
Permanent URI for this collectionhttps://hdl.handle.net/11147/4072
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Article Citation - WoS: 18Citation - Scopus: 22Prediction of Lignin and Extractive Content of Pinus Nigra Arnold. Var. Pallasiana Tree Using Near Infrared Spectroscopy and Multivariate Calibration(Taylor and Francis Ltd., 2009) Üner, Birol; Karaman, İbrahim; Tanrıverdi, H.; Özdemir, DurmuşDetermination of quality parameters such as lignin and extractive content of wood samples by wet chemistry analyses takes a long time. Near infrared (NIR) spectroscopy coupled with multivariate calibration offers a fast and nondestructive alternative to obtain reliable results. However, due to the complexity of the spectra obtained from NIR, some wavelength selection is generally required to improve the predictive ability of multivariate calibration methods. Pinus nigra Arnold. Var. pallasiana is the second most growing pine species in Turkey. Even though its rotation period is very high, around 120 years, the forest products industry has widely accepted the use of Pinus nigra because of its ability to grow on a wide range of sites and its suitability to produce desirable products. In this study, 51 samples of Pinus nigra trees were collected and their lignin and extractive content were determined with standard reference (TAPPI) methods. Then, the same samples were scanned with near infrared spectrometer between 1000 and 2500 nm in diffuse reflectance mode. Multivariate calibration models were built with genetic inverse least squares method for both lignin and extractive content using the concentration information obtained from wet standard reference method. Overall, standard error of calibration (SEC) and standard error of prediction (SEP) were ranged between 0.35% (w/w) and 2.4% (w/w).Article Citation - WoS: 11Citation - Scopus: 13Near Infrared Spectroscopic Determination of Diesel Fuel Parameters Using Genetic Multivariate Calibration(Taylor and Francis Ltd., 2008) Özdemir, DurmuşThe use of full spectral region from near infrared spectroscopic analysis does not always end up with a good multivariate calibration model as many of the wavelengths do not contain necessary information. Due to the complexity of the spectra, some of the wavelengths or regions may, in fact, disturb the model-building step. Genetic algorithms are one of the useful tools for solving wavelength selection problems and may improve the predictive ability of conventional multivariate calibration methods. This study demonstrates application of genetic algorithm-based multivariate calibration to near infrared spectroscopic determination of several diesel fuel parameters. The parameters studied are cetane number, boiling and freezing point, total aromatic content, viscosity, and density. Multivariate calibration models were generated using genetic inverse least squares (GILS) method and used to predict the diesel fuel parameters based on their near infrared spectra. For each property, a different data set was used and in all cases the number of samples was around 250. Overall, percent standard error of prediction (%SEP) values ranged between 2.48 and 4.84% for boiling point, total aromatics, viscosity, and density. However, %SEP results for cetane number and freezing point were 11.00% and 14.86%, respectively.Article Citation - WoS: 23Citation - Scopus: 26Development of Practical Hplc Methods for the Separation and Determination of Eggplant Steroidal Glycoalkaloids and Their Aglycones(Taylor and Francis Ltd., 2008) Eanes, Ritchie C.; Tek, Neslihan; Kırsoy, Öyküm; Frary, Anne; Doğanlar, Sami; Almeida, Adelia E.A practical set of HPLC methods was developed for the separation and determination of the eggplant steroidal glycoalkaloids, solanine, chaconine, solasonine, solamargine, and their aglycones, solasodine and solanidine. A gradient method was initially developed, but proved to be neither robust nor practical. Three separate isocratic methods using acetonitrile and ammonium dihydrogen phosphate were developed and shown to be more repeatable, less subject to fluctuations in mobile phase composition, and less time consuming. The effect of adjusting buffer pH, column temperature, and buffer type (triethylammonium phosphate vs. ammonium dihydrogen phosphate) were evaluated. It was also discovered that, by addition of 10% methanol to the acetonitrile portion of the mobile phase, more control over the separations was possible. The use of methanol as a mobile phase entrainer greatly improved separations in some cases and its effectiveness was also dependent upon column temperature. Assessments of the method recovery, limit of detection, and limit of quantitation were made using extracts from S. melongena and S. linnaeanum.Article Citation - WoS: 2Citation - Scopus: 2Solid-Phase Microextraction (spme) Followed by On-Fiber Derivatization of Solasodine and Solanidine Aglycones of Steroidal Glycoalkaloids(Taylor and Francis Ltd., 2008) Eanes, Ritchie C.; Tek, NeslihanSolid-phase microextraction (SPME), followed by on-fiber derivatization was investigated for the analysis of the steroidal glycoalkaloid aglycones, solasodine and solanidine. The aglycones were first extracted by direct immersion of the SPME fiber in the sample medium and then derivatized on the fiber in a separate step using 1-(trimethylsilyl)imidazole (TMSI). The derivatized compounds were then desorbed from the SPME fiber and detected by GC-MS. Polydimethylsiloxane/Divinylbenzene (PDMS-DVB), Carboxen/ Polydimethylsiloxane (CAR-PDMS), and Carbowax/Divinylbenzene (CW-DVB) fibers were employed with the CW-DVB fibers being the most successful, as expected. Closed-end capillary tubes were used to hold the extraction media. Both aglycones were successfully extracted, derivatized, and detected by GC-MS. Solasodine always required derivatization, but solanidine did not. The same method was successfully applied to cholesterol so that it could be used as an internal standard. Also, using the closed-end capillary tubes, a two-phase extraction system was also investigated, whereby the fiber was only exposed to the phase in which it was presumed to be less damaged. However, in all cases, fiber degradation was significant, preventing the use of extended extraction times and limiting reuse of the fibers. However, the results represent a first look into the feasibility of the method. With the development of more suitable SPME phases, this method could potentially provide a complementary route for routine determinations of glycoalkaloids for both research and food quality control.Article Citation - WoS: 21Citation - Scopus: 23Determination of Octane Number of Gasoline Using Near Infrared Spectroscopy and Genetic Multivariate Calibration Methods(Taylor and Francis Ltd., 2005) Özdemir, DurmuşThe feasibility of rating the octane number of gasoline using near infrared (NIR) spectroscopy and three different genetic algorithm-based multivariate calibration methods was demonstrated. The three genetic multivariate calibration methods are genetic regression (GR), genetic classical least squares (GCLS), and genetic inverse least squares (GILS). The sample data set was obtained from the ftp address (ftp://ftp.clarkson.edu/pub/hopkepk/Chemdata/) with the permission of Professor. J. H. Kalivas. This data set contains the NIR spectra of 60 gasoline samples collected using diffuse reflectance as log (I / R) with known octane numbers and covers the range from 900 to 1700 nm in 2 nm intervals. Of these 60 spectra, 20 were used as the calibration set, 20 were used as the prediction set, and 20 were reserved for the validation purposes. Several calibration models were built with the three genetic algorithm-based methods, and the results were compared with the partial least squares (PLS) prediction errors reported in the literature. Overall, the standard error of calibration (SEC), standard error of prediction (SEP), and standard error of validation (SEV) values were in the range of 0.15-0.32 (in the units of motor octane number) for the GR and GILS, which are comparable with the literature. However, GCLS produced relatively large results (0.36 for SEC, 0.39 for SEP and 0.52 for SEV) when compared with the other two methods.Article Citation - WoS: 5Citation - Scopus: 6Synthesis, Spectroscopic Characterization and X-Ray Crystal Structures of Oxo-Bridged Oxo(haloaryl) Imido Hydrotris(3,5-Dimethylpyrazolyl)borate Molybdenum(v) Complexes(Taylor and Francis Ltd., 2005) Sözüer, Hikmet Işıl; Dülger İrdem, Seçkiner; Jeffery, John J.; Hamidov, HayrullahReaction of the oxomolybdenum(V) precursor [MoTp*(O)Cl2] (Tp* = hydrotris(3,5-dimethyl-1-pyrazolyl)borate) with m-fluoroaniline, H2NC6H4F, in toluene afforded the pair of geometric isomers of [MoTp*(O)Cl](μ-O)[MoTp*(Cl)(≡NC 6H4F)] (1a, cis; 1b, trans). Similarly the reaction with m-iodoaniline yielded the compound [MoTp*(O)Cl](μ-O)[MoTp*(Cl) (≡NC6H4I)] (2). This is a new synthetic method for preparing Mo-O-Mo bridged oxo(imido) molybdenum(V) species by double deprotonation of the anilines. The complexes were characterized by IR and 1H-NMR. spectroscopy, FAB mass spectrometry, elemental analysis and X-ray crystallography which revealed that the two chloro ligands are trans to each other in 1b and 2, whereas they are cis to each other in 1a. All compounds have Mo-O-Mo linkages and near linear arylimido moieties.