Search results for "analytical"
showing 10 items of 9586 documents
Developmentand applicationof sensitivemass spectrometric methodsfor the effectivedetermination of polycyclic aromatic hydrocarbons in food
2018
Promocijas darbā tika izstrādāta inovatīva paraugu sagatavošanas metode policiklisko aromātisko ogļūdeņražu (PAH) noteikšanai. Izstrādātā metode uzrādīja teicamas pielietošanas spējas četru prioritāro PAH noteikšanā. Pirmo reizi Orbitrap masspektrometra analītiskās spējas tika piemērotas un izvērtētas PAH noteikšanai tumšajā šokolādē, izmantojot atmosfēras spiediena fotojonizācijas jonu avotu. Izstrādātā metode pavēra jaunas iespējas PAH rutīnās analīzēs. Darbā tika izstrādātas un izvērtētas divas gāzu hromatogrāfijas – masspektrometrijas metodes PAH noteikšanai īpaši zemos piesārņojuma daudzumos. Īpaša uzmanība promocijas darbā tika veltīta riskiem, kas saistīti ar kūpinātās gaļas produktu…
Selēna halogenīdi kā jaunu heterociklisku savienojumu iegūšanas avots
2017
Mūsdienās selēnsaturošo savienojumu ķīmija ir kļuvusi par organiskās, medicīniskās un materiālķīmijas nozīmīgu daļu, īpašu uzmanību pievēršot iepriekš nezināmu savienojumu iegūšanai un to īpašību izpētei. Selēna uzņemšana kopā ar citiem mikroelementiem nepieciešama organisma normālai, pilnvērtīgai funkcionēšanai. Pastāvot nepietiekamai organisma apgādei ar selēnu, pavājinās tā imūnreakcijas. Selēnam arī piemīt īpašības, kas samazina audzēju attīstības risku. Promocijas darbā ir atspoguļoti pētījumi par jaunu slāpekli saturošu heterociklisku savienojumu sintēzi izejot no selēna (II, IV) halogenīdiem. Pētījumu rezultātā ir izstrādātas jaunu selēnu saturošu heterociklisku savienojumu sintēzes …
Analītiskās pieejas izveide bioloģiski aktīvu polifenolu raksturošanai lignocelulozes biomasā
2021
Darbā ir izveidota analītiskā pieeja polifenolu savienojumu kvalitatīvai un kvantitatīvai analīzei alkšņu mizās un kviešu salmos. Izmantojot hromatogrāfiskās un spektrofotometriskās metodes veikta diarilheptanoīdu un flavonoīdu-lignīna kompleksu identifikācija un puskvantitatīva noteikšana, dominējošo savienojumu (oregonīna, tricīna-lignīna oligomēru) kvantificēšana. Orientējoties uz bioloģisko aktivitāti veikta attīrīšana, iegūstot tos ar augstu hromatogrāfisko tīrību (≥ 90%, LC-MS). Tie raksturoti kā laboratorijas references materiāli. Kviešu salmu ekstraktu bioloģiskā aktivitāte raksturota ar antioksidanto aktivitāti, bet oregonīnam pierādīta inovatīva labvēlīga ietekme uz reproduktīvo s…
Determination of the crystallinity of TiO2 photocatalysts
2018
Abstract This study reports a new simple method to determine the crystallinity of anatase and rutile TiO2 photocatalysts. The crystallinity degree of various anatase and rutile samples was estimated by XRD analysis from the ratio among the full width at half maximum intensities of the main diffraction peaks of anatase or rutile and the (111) peak of CaF2 as internal standard. The photocatalytic activity of selected powders was tested employing the photodegradation of 4-nitrophenol in aqueous solution as probe reaction. The results showed that the photoactivity of the investigated samples increased with increasing crystallinity and crystallite size.
Photoactivity of Nanostructured TiO2 Catalysts in Aqueous System and their Surface Acid-Base, Bulk and Textural Properties
2007
This work reports on the characterisation and determintion of the photocatalytic activity of some TiO2 catalysts prepared using TiCl4 as precursor. The samples, consisting of suspensions, dispersions or powders of nanonstructured anatase or rutile phases, were obtained in very mild conditions, i.e., by boiling the solution obtained after hydrolysis of TiCl4 at atmospheric pressure: it is worth noting that no calcination was necessary to obtain photoactive phases. The samples were characterised by X-ray diffraction (XRD), determination of the BET specific surface area (SSA), scanning electron microscopy (SEM) observations and diffuse reflectance spectroscopy (DRS). FT-IR spectroscopy was use…
Clean analytical method for the determination of propoxur
1995
Abstract A method has been developed for the determination of propoxur, a carbamate pesticide, by means of its reaction with p-aminophenol (PAP). The method involves the reaction, in the presence of KIO4, between the quinoneimine form of PAP and the deprotonated form of 2-isopropoxyphenol, obtained by the alkaline hydrolysis of propoxur, to provide an indophenol dye which absorbs at 600 nm. The analysis is carried out in a flow system and, after the measurement step, the waste, the reaction product and the unreacted derivatising agent is detoxified in a UV-irradiated coil placed after the measurement flow-cell and after mixing the waste with a TiO2(anatase) catalyst slurry, which can be reu…
Preparation and characterization of Al2O3 supported TiO2 catalysts employed for 4-nitrophenol photodegradation in aqueous medium
1998
Abstract In this paper the preparation and some bulk and surface characterizations of set of Al2O3 supported TiO2 photocatalysts are reported. The powders were home prepared by a wet impregnation method using titanium (IV) isopropylate. The impregnation was followed by thermal treatments and this procedure was repeated several times in order to obtain samples with different amounts of TiO2. The solids were characterized by X-ray diffraction, specific surface area determination, scanning electron microscopy coupled with an electron microprobe used in an energy-dispersive mode and diffuse reflectance spectroscopy. Moreover, all of them were tested as photocatalysts by using different kinds of…
Photon absorption by aqueous TiO2 dispersion contained in a stirred photoreactor
1991
We present a simple experimental method which allows the evaluation of the absorbed photon flow. The method is based on measurements of transmitted photon rates (by means of standard actinometer solutions) for different reactor thicknesses and/or catalyst concentrations. The method was applied to phenol degradation reaction carried out in a stirred batch phtotoreactor containing aqueous TiO 2 (anatase) dispersion, directly irradied by a 1,500 W Xe lamp
Reactive direct current magnetron sputtered TiO2 thin films with amorphous to crystalline structures.
2008
International audience; TiO2 thin films were deposited on soda–lime glass substrates by reactive direct current magnetron sputtering in a mixture of pure argon and oxygen. The influence of both the deposition time, td, and the post-annealing treatments on the films morphology, composition and structure was analyzed by scanning electron microscopy, ellipsometry, X-ray photoelectrons spectroscopy, X-ray diffraction (XRD) and Raman spectroscopy. Amorphous TiO2 was obtained for the shortest deposition time, td=15 min. Increasing td up to 30 min, poorly crystallized anatase and rutile phases were formed together with amorphous TiO2, as was revealed by complementary XRD patterns and Raman spectra…
Study of surface layers and ejected powder formed by oxidation of titanium substrates with a pulsed Nd:YAG laser beam.
2009
Laser treatment of a titanium surface at certain conditions initiates the formation of titanium oxide layers as well as micro (nano) scale powder ejected from the surface of the substrate. The resultant morphology of the surface as well as the size and the structure of the particles are all strongly dependent on the treatment parameters (laser fluence, pulse frequency, overlap parameter, etc.). In this study, titanium substrates were treated with an industrial pulsed Nd:YAG laser in air, with varying parameters. Surface layers and ejected materials were compared using scanning and transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The rutile phase of TiO(2) dominate…