A reversed phase liquid chromatographic method is proposed for the analysis of basic hair dyes (raw materials and colourant formulations). The performance of the method was enhanced by introducing postcolumn on-line p...
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A reversed phase liquid chromatographic method is proposed for the analysis of basic hair dyes (raw materials and colourant formulations). The performance of the method was enhanced by introducing postcolumn on-line photochemical derivatisation in combination with a diodearray Detector. On-line photoderivatisation provided an effective way of selectively transforming the analytes to compounds with different spectral properties. For each analyte two characteristic UV-Visible spectra (photoreactor on and off) were obtained with the same mobile phase and this information in combination with the chromatographic data (k' at pH 3.0 and 4.5) enabled the unambiguous identification of both commonly used, approved, and banned basic hair dyes. Additionally, this approach was found useful to improve the method sensitivity, allowing the determination of analytes present in low concentration (0.03 %) in complex commercial formulations.
A high performance liquid chromatographic (HPLC) procedure was developed for the determination of domoic acid (DA) in seafood, including on-line sample purification. Unpurified aqueous methanol extracts of tissue samp...
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A high performance liquid chromatographic (HPLC) procedure was developed for the determination of domoic acid (DA) in seafood, including on-line sample purification. Unpurified aqueous methanol extracts of tissue samples were partially purified with a cyano precolumn cartridge. Separation was performed on a reverse-phase C-18 column with gradient elution, and UV detection. UV spectra were acquired for confirmation. Analyte recoveries from 89% to 100% were obtained for a variety of tissues. The detection limit with confirmation by UV spectrum was 0.1 mug/g. The method eliminates the use of a manual sample cleanup step. In contrast to other published procedures, the method is insensitive to NaCl, which may be present at high concentrations in some seafood samples. Further, tryptophan does not interfere.
A confirmatory and quantitative technique is developed for domoic acid (DA) in seafood samples which is based on methanol-water extraction, separation by reverse phase liquid chromatography, a ninhydrin post-column de...
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A confirmatory and quantitative technique is developed for domoic acid (DA) in seafood samples which is based on methanol-water extraction, separation by reverse phase liquid chromatography, a ninhydrin post-column derivatization of the acid, and UV detection at 402 nm. Tissue samples containing as low as 0.3 mug DA/g analyzed by a direct method using 242 nm can be confirmed by this technique. The linear range is excellent (1 ng to 4 mug) with a linear correlation coefficient of 0.994. Spike recovery of DA was 93% at a tissue concentration of 10 mug DA/g. The method was applied successfully to mussels, crabs, oysters, razor clams, and anchovies.
C-18 Empore extraction disks were used for the isolation and trace enrichment of different groups of pesticides from river water and artificial sea water at concentration levels of 0.2, 5 and 20 mug/l [chlorotriazines...
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C-18 Empore extraction disks were used for the isolation and trace enrichment of different groups of pesticides from river water and artificial sea water at concentration levels of 0.2, 5 and 20 mug/l [chlorotriazines, (atrazine and simazine), their dealkylated metabolites, (deethyl- and deisopropylatrazine), organophosphorus (parathion-ethyl), phenylurea (linuron), anilide (propanil), carbamate (aldicarb and carbofuran) and carbamate transformation products (aldicarb sulfoxide, aldicarb sulfone and 3-hydroxy-7-phenol carbofuran]. The extraction disks allowed high flow rates thus 51 samples could be processed within 2h. 30 min. For most of the pesticides the recoveries, as determined by liquid chromatography with diode array detection (LC-DAD), varied from 74 up to 125% with coefficients of variations (CV) of 5-10%, whereas for the carbamate transformation products the recoveries were in the range of 30-35% having a CV of 17-21%. At spiking level of 0.2 mug/l the dealkylated triazine metabolites and the carbamate transformation products were not detected at all.
A method is described for the quantitative determination of the sun-screen agent Uvinul T-150 in cosmetic products. It is based on a simple extraction into acidic THF and a HPLC determination with gradient elution and...
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A method is described for the quantitative determination of the sun-screen agent Uvinul T-150 in cosmetic products. It is based on a simple extraction into acidic THF and a HPLC determination with gradient elution and diode array detection, using a column packed with 5-mu-m Lichrosorb RP-18. The detection limit is 10 ng and linearity is observed up to 5-mu-g injected. Other sun-screen agents, commonly used in the finished products, have been analyzed and their chromatographic parameters are reported. The method has been applied for determiningUvinul T-150 and all the compounds considered in some cosmetic samples of different polarity.
Fungal chemotaxonomy (that part dealing with secondary metabolites) has often been based on thin layer chromatography (TLC) and visual or UV inspection of separated spots, before and after different chemical treatment...
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Fungal chemotaxonomy (that part dealing with secondary metabolites) has often been based on thin layer chromatography (TLC) and visual or UV inspection of separated spots, before and after different chemical treatments. The identity of a small proportion of the spots can be suggested based on known internal and external standards. In most chemotaxonomical studies it is impossible to isolate, purify and identify all secondary metabolites produced, due to restraints of time and resources. High performance liquid chromatography (HPLC) of fungal extracts may have some advantages over TLC, but the problems mentioned above remain. These problems have been approached by using an alkylphenone retention time index in a reversed phase HPLC system combined with the use of a diodearray UV-VIS detector. High performance thin layer chromatography is used for further confirmation of identity of the secondary metabolites. A particular advantage of this method is that the number of biosynthetic families or groups (''chemosyndromes'') can be detected, as biosynthetically related metabolites usually have the same chromophores and UV-VIS spectra. Results obtained from Penicillium, Aspergillus and Fusarium species have shown that each species produces 5 to 15 different biosynthetic families of secondary metabolites, indicating that good chromatography data may be sufficient to identify species in the three genera. The use of the technique is exemplified by data on Aspergillus and Talaromyces species.
Three cases are described. Case 1: kinetic studies often need high time resolution measurements in order to follow the pattern of reactions taking place during the experiment. This is often laborious to achieve with t...
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Three cases are described. Case 1: kinetic studies often need high time resolution measurements in order to follow the pattern of reactions taking place during the experiment. This is often laborious to achieve with the collection of fractions for chromatographic separation. Some tool for separation is, however, necessary in order to decompose the concentrations of reactants products and intermediate species. The spectra of the intermediates may not be known at the time when the kinetic studies are needed. With unknown spectra there are still possibilities to use spectroscopy and multivariate techniques to obtain qualitative information. Case 2: it is possible to use Partial Least Squares (PLS) in order to describe the chromatographic profiles for the species even if the separation is insufficient for traditional peak measurement methods. This requires that mixtures are available with known concentrations of the species to be determined. Case 3: with modern diodearray liquid chromatography detectors there is the possibility to capture the chromatogram and the spectra at the same time. The ability to reproduce the chromatographic profile between samples makes it possible to use the Generalized Rank Annihilation Method (GRAM) possible. Whereas PLS only treats one spectrum at a time, this method treats the full two-dimensional chromatogram as an entity. The GRAM calibration is claimed to be insensitive to interfering species which are not present in the calibration. Limitations are that GRAM requires a linear detector response and very good repeatability of the retention time. The use of GRAM for calibration with Teal samples is demonstrated.
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