Method for on-line derivatization and separation of aspartic acid enantiomer in pharmaceuticals application by the coupling of flow injection with micellar electrokinetic chromatography

A novel, easy and accurate capillary electrophoresis (CE) coupled with flow injection (FI) method for the separation and determination of aspartic acid (Asp) enantiomers by on-line derivatization had been developed, and it had been applied to the real sample for the first time. The derivatization reagents were o-phthalaldehyde (OPA) and mercaptoethanol (ME), which were obtained easily, the chiral selector was beta-cyclodextrin (beta-CD), the micellar chemical was sodium dodecyl sulfate (SDS), and the modifier was methanol. By on-line derivatization, aspartic acid enantiomers were automatically and reproducibly converted to the ultraviolet (UV)-absorbing diastereoisomer derivates, which were separated by micellar electrokinetic chromatography (MEKC). According to the factors affecting the separation and sensitivity of aspartic acid enantiomer and other amino acids in the real sample, the pH value and concentration of the buffer, the concentration of beta-CD and SDS, the volume percentage of the methanol (v/v) in the buffer, the applied voltage and the conversion time were selected as the investigating variates. Under the investigated separation conditions, D-aspartic acid (D-Asp), L-aspartic acid (L-Asp) and other four amino acids achieved the baseline separation in not only the standard mixture of amino acids but also the real sample (Compound Amino Acid Injection (6AA)). The repeatability (defined as relative standard deviation (RSD), n = 5) was 4.0% and 4.0% with peak area evaluation, and 4.2% and 3.7% with peak height evaluation for D-Asp and L-Asp in the real sample. Recovery at added standard levels of 1.0, 3.0 and 6.0 mM was 92%, 104% and 109%, respectively.     

Liquid chromatographic determination of nitroaromatics in water following solid phase extraction,pre-column reduction and derivatization

Summary A selective and sensitive method for determination of nitroaromatics is described. The analytes were reduced to corresponding primary amines with iron powder and then derivatized with fluram in citrate buffer to form pyrrolinones. The highly fluorescent pyrrolinones were isolated and preconcentrated by octadecylsilane solid phase extraction cartridge followed by reversed-phase, high-performance liquid chromatographic analysis. Detection was at 395–495 nm. Various aspects such as the reduction process, derivatization, solid phase extraction and chromatographic separation were optimized. Analysis time was relatively short due to a special design for successive reduction and preconcentration. Limits of detection for 3-nitrophenol, nitrobenzene, 4 and 2-nitrotoluene were less than 60, 12, 60 and 280 ng L^–1 respectively.     

HPLC Determination of Amino Acids by Pre-Column Fluorescence Derivatization with Carbazole-9-yl-Acetyl Chloride

Atpresentseparationsandquantitativedeterminationsofaminoacidsbymeansofnewfluorescencereagentsforpre-columnorpost-columnderivatizationinRP-HPLCarestillanactivefiled,developmentshavingbeensummarizedbySnyder'.MostaminoacidsdonotshowUVabsorptionin220-254urn,henceinordertoincreasedetectionsensitivityandimproveselectivity,generallyderivatizationreagentsareemployed.Phenylisothiocyanate(PITC)',OPAand3,5-dinitrobenzoylchloride3arewellknownderivatizationreagefltsforthedeterminationofaminocompounds…     

Liquid chromatographic determination of nine N-methylcarbamates in drinking water

A multi-residue method for the simultaneous extraction from drinking water using solid-phase extraction on LiChrolut EN [poly(styrene-divinylbenzene), PSDVB] and determination of nine N-methylcarbamate pesticides (NMCs) (aldicarb, its metabolites i.e. aldicarb sulfone and aldicarb sulfoxide and carbaryl, carbofuran, dioxacarb, ethiofencarb, methomyl and propoxur) using reversed-phase liquid chromatography was studied. A 1000-fold pre-concentration was achieved and the method was used for determination of the nine pesticides in water, with limits of detection in the range 3-15 ng L(-1). For all compounds the recoveries determined at the 0.1 and 1 microg L(-1) level generally ranged from 85 to 104% with relative standard deviations (RSD) of 1.4-8.8%.     

Simultaneous chiral analyses of multiple analytes: case studies, implications and method development considerations

The field of chiral separations had a modest beginning some two decades ago. However, due to rapid technological advancement coupled with simultaneous availability of innovative chiral stationary phases and novel chiral derivatization agents, the field of chiral separations has now totally outpaced many other separation fields. Keeping pace with rapid changes in the field of chiral separations, investigators continue to add stereoselective pharmacokinetic, pharmacodynamic, pharmacologic and toxicological data of new and/or marketed racemic compounds to the literature. Examination of the evolution of chiral separations suggests that in the beginning many investigators attempted to separate and quantify a single pair of enantiomers, adopting either direct (separation made on a chiral stationary phase) or indirect (separation made following precolumn conversion of enantiomers to corresponding diastereomers) approaches. However, more recent trends in chiral separations suggest that investigators are attempting to separate and quantify multiple pairs of enantiomers with available technologies. Added to this, some interesting trends have been observed in many of the recently reported chiral applications, including preferences regarding internal standard selection, mobile phase contents and composition, sorting out issues with mass spectrometric detection, determination of elution order, analytical manipulations of metabolite(s) without reference standards and addressing some specificity-related issues. This review mainly focuses on chiral separations involving multiple chiral analytes and attempts to justify the need for such chiral separations involving multiple analytes. In this context, several cases studies are described on the utility and applicability of such chiral separations under discrete headings to provide an account to the readership on the implications of such tasks. The topics of case studies covered in this review include: (a) therapy markers--differentiation from drug abuse and/or applicability in forensics; (b) role in pharmacogenetic/polymorphic evaluation; (c) monitoring and understanding the role of parent and active metabolite(s) in clinical and preclinical investigations; (d) exploration on the pharmacokinetic utility of an active chiral metabolite vis-a-vis the racemic parent moiety; (e) understanding the chirality play in delineating peculiar toxic effects; (f) exploration of chiral inversion phenomenon, and understanding the role of stereoselective metabolism. For the further benefit of readership, some select examples (n = 19) of the separation of multiple chiral analytes with appropriate information on chromatography, detection system, validation parameters and applicable conclusion are also provided. Finally, the review covers some useful considerations for method development involving multiple chiral analytes.     

衍生化气相色谱—质谱法测定氢化法制备的对氨基酚及其杂质

研究用衍生化气相色谱－质谱法 测定硝苯催化法生产的对氨基酚及其中杂质苯胺，４、４＇－二氨基二苯醚等。探讨了对氨基酚的萃取条件及色谱行为，选择了最佳衍生化方法。     

Determination of glutathione in pharmaceuticals and cosmetics by HPLC with UV and fluorescence detection

Summary A selective HPLC determination of reduced glutathione (GSH) in pharmaceutical and cosmetic formulations is described based on prechromatographic derivatization with 4-(6-methylnaphthalen-2-yl)-4-oxo-2-buteneoic acid. The derivatization reaction is rapid under mild reaction conditions (10 min at ambient temperature and pH 7.5) and the excess reagent can be removed by liquid-liquid extraction. The thiol adducts were chromatographed on a C-8 column using 0.05 M triethylammonium phosphate (pH 4.0) — acetonitrile 68∶32 (v/v), as the mobile phase; UV and fluorescence detection (l_em 450 nm, l_exc 300 nm) were both used. The structure of the thiol adducts was confirmed by¹H and¹³C NMR spectra using sodium methanethiolate as thiol nucleophile. This work constitutes part of the thesis for the “Dottorato di ricerche” of Dr. Roberto Gotti.     

Improved supercritical fluid extraction of sulphonamides

Summary Different ways used for enhancing the yield of sulphonamides leached from solid supports are reported. Supercritical CO₂ and methanol-modified CO₂ were used as extractants of the target analytes and the impregnation of the solid sample with buffer, derivatization of the analytes and ion-pair formation were assessed. Only the sulphonamide/tetramethyl-ammonium ion-pairs are quantitatively extracted from the solid supports using pure supercritical CO₂, while the other modifications and the presence of a cosolvent lead to recoveries lower than 30% for most of the analytes. Individual separation/quantitation of the analytes was performed off-line using a liquid chromatograph.     

Mechanisms of oxygen- and argon-RF-plasma-induced surface chemistry of cellulose

Pure cellulose samples were Ar- and O₂-RF-plasma treated under various external plasma parameter conditions. Plasma induced macromolecular chain and pyranosidic ring cleavage mechanisms are discussed based on survey and high resolution ESCA and ATR-FTIR analysis of cellulose, discharge-exposed cellulose, and discharge-exposed and TFAA and PFPH-derivatized cellulose samples. Analyses have also been made of bothin situ andex situ post plasma oxidation reactions. The new plasma created functionalities were identified and their relative ratios were related to plasma parameters. It was found that Ar plasma treatments initiate reactions mainly associated with the cleavage of C1–C2 linkages leading to the formation of C=O and O-CO-O groups, while O₂-plasma treatments are associated with more intense pyranosidic ring (C-O-C bonds) splitting mechanisms. As a result of our detailed investigation of the high resolution C1s spectra of cellulose and carbohydrates we have reassigned the nonequivalent carbon bond affiliation (C-OH, C-O-C, and C-C) at 285–287 eV. Paper based on the results presented during the workshop of the Engineering Research Center for Plasma-Aided Manufacturing held in Madison, Wisconsin, in Spring 1996.     

Deciphering nucleic acid modifications by chemical derivatization-mass spectrometry analysis

Chemical derivatization in combination with mass spectrometry (MS) analysis is a promising strategy for the sensitive and effective analysis of nucleic acid modifications. In this review, we summarize the recent advances for deciphering modifications in DNA and RNA by chemical derivatization-MS analysis.