Search results for " Spectroscopy"
showing 10 items of 6851 documents
Taxane analysis by high performance liquid chromatography-Nuclear magnetic resonance spectroscopy ofTaxus species
1998
High performance liquid chromatography–nuclear magnetic resonance spectroscopic analyses of taxane diterpenoids from three Taxus species were carried out employing a stopped-flow technique. Several taxanes have been identified from 500 mg leaf samples without prior isolation. © 1998 John Wiley & Sons, Ltd.
Lignans from Torreya jackii identified by stopped-flow high-performance liquid chromatography–nuclear magnetic resonance spectroscopy
1999
Abstract Coupled reversed-phase HPLC–NMR spectroscopy has been applied to the rapid detection and identification of plant metabolites of Torreya jackii , a species of Taxaceae. Analysis consisted of gradient HPLC elution and directly coupled 1 H NMR (500 MHz) spectroscopic detection in a stopped-flow mode. Seven lignans were detected and their structures were elucidated, based on their HPLC– 1 H NMR spectra and MS data. The structures were confirmed by isolation of the single components followed by conventional NMR measurements.
Determination of lecithin and soybean oil in dietary supplements using partial least squares-Fourier transform infrared spectroscopy.
2008
Lecithin and soybean oil in dietary supplements were determined by Fourier transform infrared spectrometry transmission measurements in dichloromethane in combination with a partial least squares (PLS) regression. Two different PLS models were developed, using 16 synthetic mixtures of analytes in dichloromethane, making measurements in the spectral range from 931.8 to 1252.3 cm(-1) for lecithin and from 911.4 to 1246.9 cm(-1) and 1695.3 to 1774.5 cm(-1) for soybean oil. Seven products from the Spanish market with lecithin concentrations between 21.1% and 99.1% and soybean oil concentrations between 0% and 37.2% were analyzed by the proposed method and the data was compared to a chromatograp…
Literature survey of the on-line preconcentration in flow-injection atomic spectrometric analysis
1992
The literature on the use of “on-line” preconcentration in flow injection atomic spectrometric analysis is reviewed, taking into account its application both in flame and electrothermal atomic absorption methods as well as in plasma emission spectrometry. The basis of the different preconcentration approaches, such as liquid-liquid extraction, column preconcentration and “on-line” precipitation are discussed. The literature survey reveals the analytical performance of the developed methodologies.
Flow injection-spectrophotometric determination of metoclopramide hydrochloride.
1997
Abstract The determination of metoclopramide hydrochloride is spectrophotometrically determined by the Bratton-Marshall method in a flow injection assembly. The required nitrite is prepared on-line in the flow assembly by reducing a nitrate solution with the aid of a copperised cadmium solid-phase reactor. The calibration graph is linear over the range 0.5–85 mg l−1, with a relative standard deviation (RSD) of 0.89%, and sample throughput of 51 samples h−1. The method is easy and simple, and it is applied to determination of metoclopramide in some pharmaceutical formulations. The method eliminates the need for frequent preparation of unstable nitrite solutions.
Comparative Study on the Determination of Cephalexin in its Dosage Forms by Spectrophotometry and HPLC with UV-vis Detection
1997
This paper discusses the spectrophotometric determination of cephalexin as the intact cephalexin or as its acid-induced degradation product. Cephalexin can be determined in the range 1 × 10−5−18 × 10−5M with relative standard deviations of 5-1%. The limits of quantitation and detection were 10−5 and 0.3 × 10−5M, respectively. These procedures were compared with reversed-phase HPLC determination. No interference was observed in the presence of common pharmaceutical adjuvants. The H-point standard additions method was applied in order to correct for the possible presence of the cephalexin precursor, 7-aminocephalosporanic acid; this improves the selectivity of the UV-vis spectrophotometric me…
Speciation of tetraalkyllead compounds by flow injection — atomic absorption spectrophotometry
1990
The on-line demetallation of alkyllead compounds, with iodine, and further emulsification, provides a fast determination of total lead content in liposoluble matrices, such as gasolines. It can be carried out in a double channel manifold, using a magnetically well stirred dilution chamber for the emulsification of the samples, previous to their analysis by flame atomic absorption spectrophotometry. On the other hand, the different behaviour of tetraethyllead (TEL) and tetramethyllead (TML) can be employed for speciation of both compounds in the sample. The effect of the flow injection parameters on the sensitivity and accuracy has been studied and the figures of merit of the proposed method…
A new selective fluorogenic probe for trivalent cations.
2012
[EN] A new selective chromo-fluorogenic probe for Fe 3+, Cr 3+ and Al 3+ is reported. Detection limits are in the ¿M range and the fluorogenic sensing ability could be observed by the naked eye when illuminated with UV-light. No response is observed with divalent cations. © 2012 The Royal Society of Chemistry.
Chromium speciation in liquid matrices: a survey of the literature
2000
A thorough review of the literature published (1983 - March 1999) on chromium speciation in liquid samples is presented, and analytical techniques used in the 404 articles are summarized. The discussion focuses on atomic spectrometric techniques, which are mainly employed for chromium speciation in liquid matrices (134 articles). Details on the type of pretreatment, species, samples, techniques and analytical features of the methodologies proposed are given.