Search results for " Ultraviolet"
showing 10 items of 337 documents
Comparison of different sorbents for on-line liquid-solid extraction followed by high-performance liquid chromatographic determination of nitrogen-co…
1998
Abstract LiChrolut EN [poly(styrene-divinylbenzene), PSDVB], Carbograph (graphitized carbon black, GCB), Isolute CN (cyanopropylsilica), Isolute C 2 (ethylsilica), and LiChrospher RP18 (octadecylsilica) were studied for on-line solid-phase extraction of twelve nitrogen containing pesticides from water. Determination (UV 210 nm) was performed with a Spherisorb C 8 analytical column and an acetonitrile-water gradient. The mean recoveries from 50 ml ranged from 83% for RP18 to 44% for GCB, and decreased in the following order: RP18, CN, LiChrolut EN, C 2 , and GCB. GCB showed poor recoveries due to incomplete desorption with the acetonitrile-water gradient used, and memory effects were detecte…
Resolution of overlapped non-absorbing and absorbing solutes using either an absorption null-balance detection window or multivariate deconvolution a…
2004
Abstract Non-absorbing alkyl ether sulfates (AES) can be separated using anthraquinone-2-carboxylic acid (AQCA) as a probe; however, absorbing alkyl benzene sulfonates (ABS), if present, interfere indirect detection of most AES oligomers. Overcoming of this interference, as well as the simultaneous characterisation and evaluation of AES, fatty acids and ABS, was accomplished by using a diode-array detector and the procedures here discussed. First, it was shown that ABS can be made undetectable by using a 9 nm wide and 227 nm centred charge-absorptivity null-balance detection window (NBDW), where its contribution to the absorbance cancels the dilution effects that its presence induces on the…
Sensitive determination of aliphatic amines in water by high-performance liquid chromatography with chemiluminescence detection.
2004
A sensitive method has been developed for liquid chromatographic determination of short aliphatic amines in water samples. Analytes are preconcentrated and dansylated on solid sorbents (C18 solid-phase extraction cartridges). The dansyl derivatives are chromatographed and post-column mixed with peroxyoxalate (TCPO) and H2O2 in order to perform chemiluminescence detection. Optimal results have been obtained using a sample volume of 5 ml. The method has been applied to the quantification or screening of several aliphatic amines: methylamine, ethylamine, butylamine, diethylamine, pentylamine and hexylamine. The screening procedure has been developed including also polyamines (putrescine, cadav…
Backward transition radiation in the extreme ultraviolet region as a tool for the transverse beam profile diagnostic
2014
The present article summarizes the results of two experiments which were performed to study the radiation properties of backward transition radiation (BTR) in the extreme ultraviolet (EUV) region. This wavelength region is of particular interest for transverse beam profile imaging, because the spatial resolution is improved as a result of the reduced contribution in the imaging process of the fundamental diffraction limit. In addition, the influence of coherent effects in the transition radiation emission process, which have been observed in the visible region, might be mitigated. The first experiment, dedicated to the investigation of the BTR angular characteristics, indicates that the rad…
Synthesis and Spectroscopic Properties of Silica−Dye−Semiconductor Nanocrystal Hybrid Particles
2010
We prepared silica-dye-nanocrystal hybrid particles and studied the energy transfer from semiconductor nanocrystals (= donor) to organic dye molecules (= acceptor). Multishell CdSe/CdS/ZnS semiconductor nanocrystals were adsorbed onto monodisperse Stöber silica particles with an outer silica shell of thickness 2-23 nm containing organic dye molecules (Texas Red). The thickness of this dye layer has a strong effect on the energy transfer efficiency, which is explained by the increase in the number of dye molecules homogeneously distributed within the silica shell, in combination with an enhanced surface adsorption of nanocrystals with increasing dye amount. Our conclusions were underlined by…
Evaluation of the pH effect of formulations on the skin permeability of drugs by biopartitioning micellar chromatography☆
2004
Dermal absorption of chemicals is an area of increasing interest for the pharmaceutical and cosmetic industries, as well as in dermal exposure and risk assessment processes. Biopartitioning micellar chromatography (BMC) is a mode of reversed phase micellar chromatography that has proved to be useful in the description and prediction of several pharmacological properties of xenobiotics including oral drug absorption, ocular and skin drug permeability. The present paper deals with the application of biopartitionig micellar chromatography to evaluate the pH effect on the skin permeability of twelve non-steroidal anti-inflammatory drugs and lidocaine. For this purpose the BMC retention of the w…
Biopartitioning micellar chromatography: an in vitro technique for predicting human drug absorption.
2001
The main oral drug absorption barriers are fluid cell membranes and generally drugs are absorbed by a passive diffusion mechanism. Biopartitioning micellar chromatography (BMC) is a mode of micellar liquid chromatography that uses micellar mobile phases of Brij35 under adequate experimental conditions and can be useful to mimic the drug partitioning process in biological systems. In this paper the usefulness of BMC for predicting oral drug absorption in humans is demonstrated. A hyperbolic model has been obtained using the retention data of a heterogeneous set of 74 compounds, which shows predictive ability for drugs absorbed by passive diffusion. The model obtained in BMC is compared with …
Automated analysis of quetiapine and other antipsychotic drugs in human blood by high performance-liquid chromatography with column-switching and spe…
2004
Abstract An automated HPLC method with column switching is described for the determination of quetiapine, clozapine, perazine, olanzapine and metabolites in blood serum. After clean-up on silica C8 material (20 μm particle size) drugs were separated on ODS Hypersil C18 material (5 μm; column size 250 mm × 4.6 mm i.d.) within 25 min and quantified by ultraviolet (UV) detection at 254 nm. The limit of quantification ranged between 10 and 50 ng/ml. At therapeutic concentrations of the drugs, the inter-assay reproducibility was below 10%. Analyses of drug concentrations in serum of 75–295 patients treated with therapeutic doses of the antipsychotic drugs revealed mean ± S.D. steady state concen…
Rapid in vitro test to predict ocular tissue permeability based on biopartitioning micellar chromatography.
2003
The drug permeability prediction across the ocular tissues is important in the development of new drugs and drug delivery strategies. Physicochemical characteristics of drugs, mainly acid-base character, hydrophobicity and the molecular size determine both their transport across the eye tissue barriers and their retention in biopartitioning micellar chromatography (BMC). An in vitro model able to describe and predict the whole cornea drug permeability is proposed. The model uses the retention of drugs in BMC and molecular weight (MW) as predictive variables. The relationships between drug retention data in BMC and their bibliographic permeability values in stroma, epithelium-plus-stroma and…
Therapeutic Monitoring of Aripiprazole by HPLC with Column-Switching and Spectrophotometric Detection
2005
Aripiprazole is a novel atypical antipsychotic drug for the treatment of schizophrenia and schizoaffective disorders (1)(2)(3). The drug is metabolized by the cytochrome P450 isoenzymes 3A4 and 2D6 (4). Because of high interindividual variability in the expression of these enzymes, the aripiprazole concentration varies among healthy individuals after administration of the drug (5). In patients, insufficient response or side effects, such as somnolence, akathisia, or nausea, may result from too low or too high drug concentrations. Therapeutic drug monitoring (TDM), which is established practice for many antipsychotic drugs (6)(7), may be helpful for patients treated with aripiprazole. We mea…