Search results for "Derivatization"
showing 10 items of 215 documents
Presence of aflatoxin M1 in pasteurized milk from Morocco
2007
Fifty four samples of pasteurized milk produced by five different dairies from Morocco were surveyed for the presence of aflatoxin M1 (AFM1) using immunoaffinity columns and liquid chromatography coupled to fluorescence detection. Confirmation of AFM1 identity in positive samples was based on the formation of AFM1 hemi-acetal derivative (AFM2a) after derivatization with trifluoracetic acid. Analytical results showed that 88.8% of the samples were contaminated with AFM1; 7.4% being above the maximum level of 0.05 microg/L set by the Moroccan and European regulations for AFM1 in liquid milk. The incidence of AFM1 in milk from these dairies was 100, 92.3, 90, 83.3 and 77.7% respectively, with …
Determination of alcohols in essential oils by liquid chromatography with ultraviolet detection after chromogenic derivatization
2013
Abstract An HPLC-UV method to determine compounds having a hydroxyl functional group in plant essential oils is developed. The sample is diluted with 1,4-dioxane and the analytes are derivatized with phthalic anhydride. The derivatives (phthalates hemiesters) are separated on a C8 column using an acetonitrile (ACN)/water gradient. Separation conditions were optimized using the DryLab® method development software. For the alcohols and phenols present in mint and rose essential oils, optimization led to a ca. 40 min gradient time and a column temperature of 8 °C. The alcohol and its derivatives were identified using HPLC with mass spectrometry (MS) detection. A large sensitivity enhancement w…
A multifunctional bioconjugate module for versatile photoaffinity labeling and click chemistry of RNA
2011
A multifunctional reagent based on a coumarin scaffold was developed for derivatization of naive RNA. The alkylating agent N3BC [7-azido-4-(bromomethyl)coumarin], obtained by Pechmann condensation, is selective for uridine. N3BC and its RNA conjugates are pre-fluorophores which permits controlled modular and stepwise RNA derivatization. The success of RNA alkylation by N3BC can be monitored by photolysis of the azido moiety, which generates a coumarin fluorophore that can be excited with UV light of 320 nm. The azidocoumarin-modified RNA can be flexibly employed in structure-function studies. Versatile applications include direct use in photo-crosslinking studies to cognate proteins, as dem…
A Quantitative Estimate of Ascorbic and Isoascorbic Acid by High Performance Liquid Chromatography: Application to Citric Juices
1993
Abstract The present report deals with the optimization and verification of a simple HPLC isocratic method useful for determining ascorbic and isoascorbic acids in standard solutions and fruit juices. Sample preparation is minimal and docs not require derivatization. The method uses an octadecyl reversed phase, a mobile phase which contains cetyltrimethyl ammonium bromide 0.05M as the ionic pair and potassium dihydrogen phosphate as a buffer, at pH=4.5, and 4-hydro-xyacetanilide as internal standard. The proposed method makes it possible to quantify ascorbic and isoascorbic acid in less than 13 minutes, with precision (C. V. 3.5%) and accuracy (recover' of 98%).
Application of solid-phase microextraction combined with derivatization to the determination of amphetamines by liquid chromatography
2004
This work evaluates the utility of solid-phase microextraction (SPME) in the analysis of amphetamines by liquid chromatography (LC) after chemical derivatization of the analytes. Two approaches have been tested and compared, SPME followed by on-fiber derivatization of the extracted amphetamines, and solution derivatization followed by SPME of the derivatives formed. Both methods have been applied to measure amphetamine (AP), methamphetamine (MA), and 3,4-methylenedioxymethamphetamine (MDMA), using the fluorogenic reagent 9-fluorenylmethyl chloroformate (FMOC) and carbowax-templated resin (CW-TR)-coated fibers. Data on the application of the proposed methods for the analysis of different kin…
On-Line Derivatization into Precolumns for the Determination of Drugs by Liquid Chromatography and Column Switching: Determination of Amphetamines i…
1996
A chromatographic system for the on-line derivatization of drugs using column switching is described. The system uses a 20 mm × 2.1 mm i.d. precolumn packed with a unmodified ODS stationary phase. This column is used for sample cleanup and enrichment of the analytes. Next, the trapped analytes are derivatized by injection of the derivatization reagent into the precolumn. Finally, the derivatives are transferred to the analytical column for their separation under reversed-phase conditions. The influence of several parameters such as the reaction time, the amount of derivatization reagent, or the system design has been studied using some amphetamines as model compounds and three derivatizatio…
o-Phthalaldehyde–N-acetylcysteine polyamine derivatives: formation and stability in solution and in C18 supports
2001
A comparative study of different derivatization procedures has been performed in order to improve the stability of the reaction products o-phthalaldehyde-N-acetylcysteine (OPA-NAC) polyamines. Procedures such as solution derivatization, solution derivatization followed by retention on a packing support, derivatization on different packing supports and on-column derivatization, have been optimized and compared. The degradation rate constant (k) of the derivative was dependent on the procedure used and on the analyte. For the spermine (the most unstable isoindol tested) k was 8 +/- 2 x 10(-2) min(-1) in solution versus 7.7 +/- 1.1 x 10(-4) min(-1) on the (C18) solid support. The results obtai…
Determination of aliphatic amines in water by liquid chromatography using solid-phase extraction cartridges for preconcentration and derivatization
2001
Bond Elut C18 solid-phase extraction cartridges were used for preconcentration and pre-column derivatization with 3,5-dinitrobenzoyl chloride (DNB) of aliphatic amines in water. Conditions for analyte preconcentration and derivatization (including the volume of sample, concentration of reagent, time of reaction and pH) were investigated, using ethylamine, isopropylamine and dimethylamine as model compounds. On the basis of these studies, a rapid and sensitive method for the determination of aliphatic amines in water is presented. The analytes are retained and purified on the cartridges and then derivatized and desorbed by drawing in succession the DNB solution and acetonitrile. The collecte…
Enhancement of retention predictions in reversed-phase liquid chromatography using reference compounds
2004
Abstract The use of reference compounds to correct errors associated with the preparation of mobile phase is studied, in order to enhance modelling of retention for optimisation purposes in reversed-phase liquid chromatography. The method fits individual retention models for a set of reference compounds, which are present in all injections. In second step, mobile-phase composition is corrected for each chromatogram, according to the fitted models of the reference compounds. The enhanced precision provided by the large number of replicates for the reference compounds is partially propagated to the retention models of the analytes. The approach is assayed in the separation of amino acids, aft…
Application of solid-phase microextraction combined with derivatization to the enantiomeric determination of amphetamines.
2005
Abstract The utility of combining chiral derivatization and solid-phase microextraction (SPME) for the enantiomeric analysis of primary amphetamines by liquid chromatography has been investigated. Different derivatization/extraction strategies have been evaluated and compared using the chiral reagent o -phthaldialdehyde (OPA)– N -acetyl- l -cysteine (NAC) and fibres with a Carbowax-templated resin coating. Amphetamine, norephedrine and 3,4-methylenedioxyamphetamine (MDA) were used as model compounds. On the basis of the results obtained, a new method is presented based on the derivatization of the analytes in solution followed by SPME of the OPA–NAC derivatives formed. The proposed conditio…