Search results for "Analyte"
showing 10 items of 303 documents
Determination of carbonyl compounds in particulate matter PM2.5 by in-tube solid-phase microextraction coupled to capillary liquid chromatography/mas…
2013
Abstract In this paper, a new procedure based on in-tube solid phase microextraction (IT-SPME)-capillary liquid chromatography hyphenated to mass spectrometry detection by using microelectrospray ionisation (CapLC–MS), has been reported. The device was proposed to quantify 12 carbonyl compounds (10 aliphatic aldehydes, an unsaturated aldehyde and a ketone) derivatized with 2,4-dinitrophenylhidrazine (DNPH) reagent in aqueous extracts of PM 2.5 . This methodology involves the on-line preconcentration of DNPH-carbonyl compounds derivatives coupled to the CapLC–MS system, efficiently providing appropriate sensitivity for the determination of the target analytes. Detection limits for the analyt…
Fourier transform infrared spectrometric determination of Ziram.
2001
A procedure has been developed for vapour-phase Fourier transform infrared determination of Ziram, a dithiocarbamate pesticide. The method is based on the evolution of CS(2), after decomposition of the dithiocarbamate with diluted H(2)SO(4) at 50 degrees C. The CS(2) evolved was swept by a carrier flow of nitrogen to a laboratory-made infrared gas cell of 39 mm pathlength and 490 mul volume. The signals were registered as a function of time. The area of peaks obtained from absorbance measurement in the wavenumber range between 1600 and 1450 cm(-1) were interpolated in a calibration line established from Ziram standards treated in the same way as samples. The method provided an absolute limi…
Comparative study of the determination of trimethylamine in water and air by combining liquid chromatography and solid-phase microextraction with on-…
2005
This work describes a new approach for the determination of trimethylamine (TMA) in water and air by liquid chromatography (LC). The assay is based on the employment of a solid-phase microextraction (SPME) fiber for sampling and for derivatization of the analyte with the fluorogenic reagent 9-fluorenylmethyl chloroformate (FMOC). The fiber, with a Carbowax-templated resin -50mum coating, was first immersed into a solution of the reagent. Once loaded with the reagent, the fiber was immersed into the water samples or exposed to the air samples in order to extract and to derivatize the analyte. Finally, the fiber was placed into a HPLC-SPME interface to desorb and transfer the TMA-FMOC derivat…
Active alkaline traps to determine acidic-gas ratios in volcanic plumes: Sampling techniques and analytical methods
2014
In situ measurements have been the basis for monitoring volcanic gas emissions for many years and—being complemented by remote sensing techniques—still play an important role to date. Con- cerning in situ techniques for sampling a dilute plume, an increase in accuracy and a reduction of detection limits are still necessary for most gases (e.g., CO2, SO2, HCl, HF, HBr, HI). In this work, the Raschig-Tube tech- nique (RT) is modified and utilized for application on volcanic plumes. The theoretical and experimental absorption properties of the RT and the Drechsel bottle (DB) setups are characterized and both are applied simultaneously to the well-established Filter packs technique (FP) in the …
Rupture Force of Single Small Drug Molecule Binding a Split Aptamer
2012
Aptamers are specific oligonucleotides (DNA or RNA) which bind small inorganic or organic molecules, large proteins or cells. In particular, the high affinity of aptamers is expected to lead to a new class of therapeutic reagents. Thus the detection and characterization of binding strength of small molecules is important for drug and medical research. Atomic force spectroscopy (AFS) with a force resolution in the piconewton range is a valuable tool for studying interactions on a single molecular level. The detection of very small target molecules less than 500 Dalton is characterized by only a few hydrogen interactions between the aptamer and the target molecules. Thus tiny rupture forces w…
Column-switching techniques for screening of diuretics and probenecid in urine samples
1994
A method based on high-performance liquid chromatography using column-switching is described for the screening of diuretics and probenecid in urine samples. The system uses a 20- x 2.1-mm i.d. precolumn, packed with a Hypersil ODS-C18, 30-microns stationary phase, for the on-line sample cleanup and enrichment. Untreated urine samples are directly injected, and the precolumn is flushed for 1 min with water to eliminate polar matrix components. The retained analytes are then back-flushed by means of a six-port switching valve onto a Hypersil ODS-C18 analytical column (5 microns, 250- x 4-mm i.d.), where they are separated using an acetonitrile/phosphate buffer (pH = 3) gradient elution. Under…
Computer simulations for bioequivalence trials: selection of analyte in BCS drugs with first-pass metabolism and two metabolic pathways.
2010
The objective of this work is to use a computer simulation approach to define the most sensitive analyte for in vivo bioequivalence studies of all types of Biopharmaceutics Classification System (BCS) drugs undergoing first-pass hepatic metabolism with two metabolic pathways. A semi-physiological model was developed in NONMEM VI to simulate bioequivalence trials. Four BCS classes (from Class I to IV) of drugs, with three possible saturation scenarios (non-saturation, saturation and saturation of only the major route of metabolism), two (high or low) dose schemes, and six types of pharmaceutical quality for the drug products were simulated. The number of investigated scenarios was 144 (4 × 3…
Micellar electrokinetic capillary chromatography for therapeutic drug monitoring of carbamazepine and its main metabolites.
1998
In carbamazepine (CBZ) therapy the concomitant monitoring of concentrations of CBZ and its metabolites is strictly recommended, primarily to avoid toxic side effects. Currently, clinical routine monitoring of CBZ is accomplished by high-performance liquid chromatography or immunological methods. In this study a micellar electrokinetic capillary chromatographic (MECC) method was developed for routine drug monitoring of CBZ and its main metabolites, carbamazepine 10,11-diol and carbamazepine 10,11-epoxide, in human serum or plasma samples. The MECC method enabled baseline separation of all analytes within 2.5 min. The assay revealed sufficient precision and sensitivity and the results of eith…
Saliva testing after single and chronic administration of dihydrocodeine.
2001
In the present study, concentrations of dihydrocodeine and its metabolites in saliva and serum were compared after single low-dose and chronic high-dosage administration of the drug. In the first investigation, blood and saliva were collected periodically from six subjects after oral administration of 60 mg dihydrocodeine. In the second study, 20 subjects on oral dihydrocodeine maintenance provided single samples of blood and saliva simultaneously. Serum protein binding of salivary analytes and their recovery from the adsorbing material of the collection device as well as pH values of saliva samples were determined. The fluids were analyzed for dihydrocodeine and the major metabolites by hi…
Computer simulations of bioequivalence trials: selection of design and analyte in BCS drugs with first-pass hepatic metabolism: linear kinetics (I).
2008
Modeling and simulation approaches are useful tools to assess the potential outcome of different scenarios in bioequivalence studies. The aim of this study is to propose a new and improved semi-physiological model for bioequivalence trial simulations and apply it for all BCS (Biopharmaceutic Classification System) drug classes with non-saturated first-pass hepatic metabolism. The semi-physiological model was developed in NONMEM VI to simulate bioequivalence trials. Parent drug and metabolite levels for both reference and test were simulated. Eight types of drugs (with high or low permeability and high or low solubility (class I to IV) and high or low intrinsic clearance) were considered in …