Search results for "Spectroscopy"
showing 10 items of 10293 documents
Critical assessment of ionization patterns and applications of ambient desorption/ionization mass spectrometry using FAPA-MS
2016
Ambient desorption/ionization mass spectrometry (MS) has gained growing interest during the last decade due to its high analytical performance and yet simplicity. Here, one of the recently developed ambient desorption/ionization MS sources, the flowing atmospheric-pressure afterglow (FAPA) source, was investigated in detail regarding background ions and typical ionization patterns in the positive as well as the negative ion mode for a variety of compound classes, comprising alkanes, alcohols, aldehydes, ketones, carboxylic acids, organic peroxides and alkaloids. A broad range of signals for adducts and losses was found, besides the usually emphasized detection of quasimolecular ions, i.e. […
A new interface to couple thin-layer chromatography with laser desorption/atmospheric pressure chemical ionization mass spectrometry for plate scanni…
2005
An interface to allow on-line qualitative and quantitative full-plate detection and analysis of compounds separated by thin-layer chromatography (TLC) is presented. A continuous wave diode laser is employed as a desorption source. Atmospheric pressure chemical ionization mass spectrometry ionizes and subsequently identifies the desorbed sample molecules. Besides direct laser desorption on untreated TLC plates, graphite particles were used as a matrix to couple in the laser power and improve the efficiency of desorption.
Flow injection near-infrared determination of ethanol in chloroform
1995
A simple and direct flow injection (FIA) procedure has been developed for the determination of the stabilizing agent ethanol in chloroform samples. The procedure is based on the use of the absorbance band of ethanol in the near-infrared (NIR) region at 2272 nm, measured in front of a reference sample of chloroform stabilized with amylene. The method developed provides a limit of detection of 0.0045% (v/v) and a dynamic range until 10% (v/v) with a typical variation coefficient of 0.4% for six independent analysis of a real sample containing approximately 1% (v/v) of ethanol. The sample injection frequency allowed by the method is 78 h−1.
Optical recognition and removal of Hg(II) using a new self-chemosensor based on a modified amino-functionalized Al-MOF
2017
Abstract We developed a simple self-chemical optical sensor for the monitoring and removal of ultra-trace levels of Hg(II) from aqueous media. The development of this sensor was based on the covalent attachment of amino-functionalized aluminum-based MOF particles with ninhydrin. The new sensor is densely coated with a chelating ligand to permit an ultra-fast, selective, pH-dependent visualization for removal of Hg(II) with detection limit (LOD∼0.494 μg L−1). Monitoring was accomplished via both a colorimetric signal visible to the naked eye as well as UV–vis absorption spectroscopy. Digital image-based colorimetric analysis has also used as a semi-quantitative analysis for determination the…
Copper, iron and zinc determinations in human milk using FAAS with microwave digestion
2000
Abstract A method for determining copper, iron and zinc in human milk was optimized and validated. It includes microwave mineralization of the sample and measuring the elements by flame atomic absorption spectroscopy (FAAS). Only 2 ml of milk is needed, and the method is free of matrix interferences. The values obtained for the detection limits (0.07; 0.07; 0.11 μg/ml milk, for copper, iron and zinc) precision of the method, intra-assay (2.9; 5.2; 6.1%RSD for copper, iron and zinc) and accuracy, evaluated using recovery assays (98.8; 100.4; 95.9% for copper, iron and zinc) show that the method is useful for the purpose mentioned. Moreover, the method is rapid and simple, and the determinati…
Influence of the differentiation system on the analytical parameters for the spectrophotometric determination of clonazepam in urine
1991
Abstract Electronic and mathematical differentiation of the ultraviolet visible spectra were compared from the study of the analytical parameters of the direct determination of clonazepam in urine samples. Third-order derivative spectra were used. The mathematical differentiation provides higher sensitivity, a lower limit of detection, and better accuracy and precision than the electronic one. The use of a diode array instrument provides lower sensitivity than that found using a conventional spectrometer; however, the limit of detection obtained in both cases is of the same order.
First‐Derivative Fourier‐Transform Infrared Determination of Oxadiazon in Commercial Herbicide Formulations
2008
Abstract A Fourier‐transform infrared (FTIR) method has been developed for the quantification of oxadiazon in herbicide formulations. The method involves the extraction of the active ingredient by sonication of the samples with CHCl3 and direct measurement of the peak area values in first‐order derivate spectra from 1770 cm−1 to 1774 cm−1 corrected with a baseline point located at 1950 cm−1 and after a 5‐point smoothing. A limit of detection (3 s) of 0.03 mg g−1 and a typical relative standard deviation (RSD) of 1.3% were found. Results obtained were comparable with those found by liquid chromatography with UV detection. The proposed method involves a 7‐times reduction in solvent consumptio…
Detection of banned drugs in sport by micellar liquid chromatography
1992
Abstract A rapid method for the determination of banned drugs in sport (including stimulants, anabolic steroids and diuretics) based on micellar liquid chromatography is proposed. The mobile phase is an aqueous solution of a surfactant (sodium dodecyl sulphate in this instance) and the stationary phase is octadecylsilica. The retention parameters of the drugs were established and the effect of a mobile phase organic modifier on the chromatographic behaviour of the compounds was studied. Improvements in efficiency were achieved by control of the temperature of the mobile phase. This method allows the direct injection of urine samples for the determination of drugs excreted free in urine: ami…
Determination of nitrogen in hydrolyzed protein formulations by continuous vapour phase FTIR.
2006
An on-line system with vapour generation (VG) and Fourier transform infrared (FTIR) spectrometric detection has been developed for the determination of free ammonium and organic nitrogen in agrochemical formulations containing hydrolyzed proteins. Commercial samples were digested, in batch mode, with sulphuric acid and the obtained solution was alkalinized on-line to transform the NH(4)(+) to NH(3) that was continuously monitored by FTIR. Free ammonium was determined in the same system after simple dilution of undigested samples with water. Different gas phase separators were assayed in order to introduce gaseous NH(3) into a home made IR gas cell of 10 cm pathlength, where the correspondin…
Analyser of chromium and/or cobalt
2003
Abstract Two stopped-flow manifolds have been proposed for individual or simultaneous determination of chromium and cobalt in water samples. Automated procedures based on multicommutation systems have emphasised the differences of their catalytic effect in luminol–hydrogen peroxide chemiluminescence reaction. A more rapid decay of signal was observed for Co for both configurations (flow injection or continuous injection). The influence of chemical and hydrodynamic variables has been studied in order to establish the robustness of method. The analysis rate was lower 1.5 min per replicate. Chemometric tools have been employed for the resolution of their contributions. Partial least squares (P…