Wenjian Lao

Headspace liquid-phase microextraction of trihalomethanes in drinking water and their gas chromatographic determination

In the present work, a novel method for the determination of trihalomethanes (THMs) such as chloroform, dichlorobromomethane, chlorodibromomethane and bromoform in drinking water has been described. It is based on coupling headspace liquid-phase microextraction (HS-LPME) with gas chromatography-electron capture detector (GC-ECD). A microdrop of organic solvent at the tip of a commercial microsyringe was used to extract analytes from aqueous samples. Three organic solvents-xylene, ethylene glycol and 1-octanol-were compared and 1-octanol was the most sensitive solvent for the analytes. Extraction conditions such as headspace volume, extraction time, stirring rate, content of NaCl and extraction temperature were found to have significant influence on extraction efficiency. The optimized conditions were 15ml headspace volume in a 40ml vial, 10min extraction time and 800rpm stirring rate at 20 degrees C with 0.3gml(-1) NaCl. The linear range was 1-100mugl(-1) for THMs. The limits of detection (LODs) ranged from 0.15mugl(-1) (for dichlorobromomethane and chlorodibromomethane) to 0.4mugl(-1) (for chloroform); and relative standard deviations (RSD) for most of THMs at the 10mugl(-1) level were below 10%. Real samples collected from tap water and well water were successfully analyzed using the proposed method. The recovery of spiked water samples was from 101 to 112%.

High performance liquid chromatographic determination of N- nitrosoamines by pre-column fluorescence derivatization with acridone-N- acetyl chloride

A sensitive high performance liquid chromatographic method for the determination of N-nitrosoamines with pre-column fluorescence derivatization has been developed. N-nitrosoamines are first changed into secondary amines using denitrosation reagent, then react with acridone-N-acetyl chloride (ARC-Cl) to produce corresponding secondary amine derivatives, which exhibit a strong fluorescence. Maximum emission for ARC derivatives is 430 nm (lambda(ex) 404 nm). The labelled derivatives are very stable, less than 4% decomposition occurs after heating at 40 degrees C for 24 h. Fluorescence intensities of derivatives are higher in neutral and alkaline than in acidic solutions. This method, in conjunction with a multi-gradient program, offers a baseline resolution of the ARC derivatives from a linear acetonitrile gradient. Separation is carried out on a reverse phase C(18) column. Derivatization and chromatographic conditions are optimized. The relative standard deviation (n=6) at an analytical concentration of 10 pmol of each N-nitroamine is less than 4.5%. The detection limits at the fmol level. The method described is also suitable for analysis of other amino compounds in different biological samples.

Electronic and vibrational spectra of a series of substituted carbazole derivatives

The FTIR and FTR spectra of halogen (Cl, Br, I) substituted carbazole and their N-acetic and propionic acids have been recorded. A number of lines have been assigned on the basis of previous studies on the parent compound and by comparisons with the characteristic vibrations of their constituent structural units as well as comparing the spectra from FTIR and FTR. Some substituent-sensitive bands and characteristic bands were found. The electronic absorption spectra of these compounds in acetonitrile were also measured and are briefly discussed.

Fluorescence properties of carbazole-N-(2-methyl)acetyl chloride and determination of amino compounds via high-performance liquid chromatography with pre-column fluorescence derivatization

A sensitive LC method for the determination of amino compounds with fluorescence detection has been developed. The reaction of fluorescent tagging reagent, namely carbazole-N-(2-methyl)acetyl chloride (CMA-Cl), with amino acids is reported. Emission maximum for the CMA derivatives of amino acids is 360 nm (λex=335 nm). In all cases, the derivatives exhibit strong fluorescence, whereas the reagent itself also exhibits fluorescence. It is found that the labelled derivatives using CMA-Cl are very stable; <4% decomposition occurs after heating at 40°C for 24 h in neutral solution. Fluorescence intensity of amino acid derivatives is higher in neutral and alkaline than in acidic solutions. This method, in conjunction with a gradient elution, offers baseline resolution of 18 amino acids including Orn from a linear acetonitrile gradient (here, Asn, Gln and Trp are not tested, the principal reasons: Gln and Asn, in a real sample hydrolysed, have been changed into Glu and Asp; Trp gives as much as 60% loss of its monosubstituted derivative under proposed derivatization conditions.). Separation of derivatives is carried out on a reversed-phase C18 column with good reproducibility. Derivatization and chromatographic conditions are optimized. The relative standard deviations (n=6) for 50 pmol of each amino acid derivative are <4.5%. The detection limits, calculated by the corresponding peak heights (in cm) by injecting successively lower concentrations until a signal-to-noise of 3:1, are 10–65 fmol for the labelled amino acids.

Determination of alcohols using condensation agent carbazole-9-acetyl-benzene-disulfonate by high performance liquid chromatography with pre-column fluorescence derivatization

SummaryA sensitive LC method for the determination of alcohols, using fluorescent condensation agent carbazole-9-N-acetylbenzne-disulfonate(CABS), has been developed. A mixture of alcohols and triethylamine catalyst in dichloromethane or chloroform is treated with CABS to give quantitative yields of esters. Emission maximum for the derivatized alcohols is 365 nm (λex 335 nm). The labeled derivatives are very stable, no significant decomposition is observed after heating in 40% at 40°C for 24 h. The method, in conjunction with a multigradient program, offers baseline resolution of common alcohol derivatives on a reversed-phase C18 column. Studies on derivatization conditions indicate that primary and secondary alcohols react very fast with CABS in the presence of triethylamine in dichloromethane or chloroform to give the corresponding fluorescent derivatives. This method is more convenient and more efficient than previous methods which require prior conversion of carboxylic acids to acyl chlorides. The separation of alcohol derivatives has good reproducibility and the rsds (n=5) for 50 pmol of each alcohol are 4%. Detection limits are at the fmol level.

CARBAZOLE-9-N-ACETYL-N-HYDROXYSUCCINIMIDE (CAHS) AS PRE-COLUMN DERIVATIZATION AGENT FOR FLUORIMETRIC DETECTION OF AMINO COMPOUNDS WITH LIQUID CHROMATOGRAPHY

A simple and sensitive LC method for the determination of amino compounds, using carbazole-N-acetyl-N-hydroxy-succinimide (CAHS) as condensation agent, has been developed.A mixture of amines is treated with CAHS, in the presence of triethylamine catalyst in non-aqueous acetonitrile or in the presence of 0.2 M borate buffer at pH 8.0–9.0 in 40% (v/v) of acetonitrile solution, to give quantitative yields of amides. Emission maximum for the derivatized amines is 365 nm (λex 335 nm). Studies on derivatization conditions indicate that amines react very fast with CAHS under proposed conditions. The method, in conjunction with a multi-step gradient, offers baseline resolution of common amine derivatives on a reversed-phase C18 column. Derivatization reaction is more convenient and more efficient than previous methods which require prior conversion of carboxylic acids to acyl chlorides. The LC separation of amine derivatives has good reproducibility. The established method is also suitable for the determination o...

Facile and Rapid Synthesis of 9H-Carbazole-9-Carboxylic Acids Under Microwave Irradiation

Abstract The reaction of halogenated 9H-carbazoles or carbazole with bromoesters in DMF under microwave irradiation readily affords a series of 9H-carbazoles-9-hydroxylic acids.

Study of the chromatographic behavior and inclusion constants of new fluorescence agents by use of cyclodextrin additives under conditions of steady- and dynamic-state equilibrium and with fluorescence detection

SummaryWe report four new derivatization agents, acridone-N-acetic acid (ARC), carbazole-9-ylacetic acid (CRA), carbazole-9-ylpropionic acid (CRP), and 2-methyl-2-carbazole-9-ylacetic acid (MCRA), with strong fluorescence emission which has low dependence on solvent polarity. The emission maxima for ARC, CRA, CRP, and MCRA were 430 nm (λex 404 nm), 368 nm (λex 335 nm), 356 nm (λex 340 nm) and 360 nm (λex 330 nm), respectively. The effects of mobile-phase composition, pH, and temperature on the liquid chromatographic retention behavior of the four fluorescence agents were investigated. An experimental model was established for calculating the inclusion constants of cyclodextrin (CD) complexes in the dynamic state, using β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) as examples, and different mobilephase compositions. On the basis of the model, the inclusion constants of the solutes in pure water (Kfw) were determined by extrapolation. The thermodynamic parameters (ΔHo and ΔSo) and dissociation constantsKam for the solutes in this chromatographic system were obtained by means of capacity factor (k) values using a corresponding model formulation.