End-column electrochemical detection for aromatic amines with high performance capillary electrophoresis

Electrochemical detection of five species of aromatic amines at a carbon fiber microdisk electrode after separation by capillary electrophoresis is described. Under the optimum conditions, the detection limit for 3,4-dihydroxybenzylamine, N,N-dimethylaniline, p-phenylenediamine, p-aminophenol and aniline sulfate was 0.9, 0.03, 0.075, 1.2 and 0.15 mu M (S/N = 3), respectively. The linear response range was 5-1000, 0.1-500, 0.5-500, 5-500 and 1-200 mu M, respectively The effect of the electrode position and buffer pH on the detection was also studied. This method is very simple, sensitive and stable for the detection of these compounds.

End-column amperometric detection of 5-fluorouracil by capillary zone electrophoresis with a carbon fiber microelectrode

A rapid and sensitive detection method for the determination of 5-fluorouracil(5-FU) in real samples such as human urine and bovine serum albumin (BSA) was described. A carbon fiber microdisk electrode was used to perform end-column amperometric detection in capillary zone electrophoresis. The detection limit was as low as 2.5x10(-7) M and the wider linear range for the concentration was between 5x10(-6) and 1x10(-4) M with a correlation coefficient of 0.995.

Separation of promethazine and thioridazine using capillary electrophoresis with end-column amperometric detection

Promethazine and thioridazine were separated and detected by capillary electrophoresis with end-column amperometric detection. The influence of pH Value on oxidation potential, the peak current and the resolution were studied and the following conditions was selected: 0.03 M Na2HPO4 and 0.015 M citric acid at pH 3.0, detection potential at 1.10 V. The detection limits of these two substances were in the range of 10(-8) mol/l. The linear range spanned two to three orders of magnitude. This method was applied to the detection of promethazine and thioridazine spiked in urine. (C) 1999 Elsevier Science B.V. All rights reserved.

Determination of sulfadiazine and sulfamethoxazole by capillary electrophoresis with end-column electrochemical detection

Capillary electrophoresis (CE) with end-column electrochemical detection (EC) of sulfadiazine (SDZ) and sulfamethoxazole (SMZ) is described. Under the optimum conditions, SDZ and SMZ were separated satisfactorily, and a highly sensitive and stable response was obtained at a potential of 1.1 V versus Ag/AgCl. Optimized end-column detection provides detection limits as low as 0.1 mu M for both compounds, which corresponds to 0.024 and 0.021 fmol with peak efficiencies of 394000 and 335000 theoretical plates for SDZ arid SMZ, respectively. The calibration graph was linear over three orders of magnitude. The relative standard deviations (n = 12) of peak currents and migration times were 2.3 and 2.7%, and 0.8 and 1.3%, respectively, for the two compounds. The proposed method was applied to the analysis of tablets and human urine samples with satisfactory results.

Self-assembly of the pre-formed inclusion complexes between cyclodextrins and alkanethiols on gold electrodes

A new kind of self-assembled monolayer (SAM) formed in aqueous solution through the pre-formed inclusion complexes (abbreviated CD . C-n) between alpha-, beta-cyclodextrins (CDs) and alkanethiols (CH3(CH2)(n-1)SH, n = 10, 14 and 18) was prepared successfully on gold electrodes. High-resolution H-1 NMR was used to confirm the formation of CD . C-n. X-ray photoelectron spectroscopy, cyclic voltammetry and chronoamperometry were used to characterize the resulting SAMs (denoted as M-CD . Cn). It was found that M-CD . Cn were more stable against repeated potential cycling in 0.5 M H2SO4 than SAMs of CH3(CH2)(n-1)SH (denoted as M-Cn), with a relative sequence of Mbeta-CD . Cn > Malpha-CD . Cn > M-Cn. In addition, an order of blocking the electron transfer between gold electrodes and redox couples (both Fe(CN)(6)(3-) and Ru(NH3)(6)(3+)) in solution, M-CD . C10 > M-CD . C14 > M-CD . C18, was observed. A plausible explanation is provided to elucidate some of the observations. (C) 1997 Elsevier Science S.A.

Gas phase derivatization of endohedral metallofullerenes R@C-82 and R-2@C-80 (R = Nd, Ce)

Endohedral metallofullerenes Ce@C-82, Ce-2@C-80, Nd@C-82 and Nd-2@C-80 undergo gas phase ion/molecule reactions with the ion system from self-chemical ionization of vinyl acetate, and exohedral derivatives are thus generated, A new heterocycle is formed from metallofullerenes and a C2H3O+ cation, Endohedral metallofullerenes show much higher reactivities than empty fullerenes during the association and the charge and proton transfer processes, The strong electron-donating character of endohedral metallofullerenes is due to their unique super-atom-like electronic structures. (C) 1997 by John Wiley & Sons, Ltd.

Microprojectile bombardment of Laminaria japonica gametophytes and rapid propagation of transgenic lines within a bubble-column bioreactor

A human acidic fibroblast growth factor gene, hafgf, was successfully transferred into Laminaria japonica (kelp) gametophytes via microprojectile bombardment using the biolistic PDS-1000/He gene gun. Following phosphinothricin screening, PCR detection and Southern blot analysis, transgenic L. japonica gametophytes were cultivated in an illuminated bubble-column bioreactor to optimize growth conditions. A maximal final dry cell density of 1,695 mg l(-1) was obtained in a batch culture having an initial dry cell density of 129.75 mg l(-1). This was achieved using an aeration rate of 1.08 l air min(-1) l(-1) culture in a medium containing 1.5 mM inorganic nitrate and 0.15 mM phosphate. In addition, the relationship between different nitrogen sources and growth of transgenic gametophytes indicated that both urea and sodium nitrate were effective nitrogen sources for cell growth, while ammonium ions inhibited growth of these gametophytes.

Optimal light regime for the cultivation of transgenic Laminaria japonica gametophytes in a bubble-column bioreactor

Fluctuating light intensity had a more significant impact on growth of gametophytes of transgenic Laminaria japonica in a 2500 ml bubble-column bioreactor than constant light intensity. A fluctuating light intensity between 10 and 110 mu E m(-2) s(-1), with a photoperiod of 14 h:10 h light:dark, was the best regime for growth giving 1430 mg biomass l(-1).

Comparative analysis of astaxanthin and its esters in the mutant E1 of Haematococcus pluvialis and other green algae by HPLC with a C30 column

A gradient reversed-phase high-performance liquid chromatography (HPLC) method using a C30 column was developed for the simultaneous determination of astaxanthin, astaxanthin monoesters and astaxanthin diesters in the green algae Chlorococcum sp., Chlorella zofingiensis, Haematococcus pluvialis and the mutant E1, which was obtained from the mutagenesis of H. pluvialis by exposure to UV-irradiation and ethyl methanesulphonate (EMS) with subsequent screening using nicotine. The results showed that the contents of total astaxanthins including free astaxanthin and astaxanthin esters ranged from 1.4 to 30.9 mg/g dry biomass in these green algae. The lower total astaxanthin levels (< 2 mg/g dry biomass) were detected in the green algae Chlorococcum sp. and C. zofingiensis. The higher total astaxanthin levels (> 16 mg/g dry biomass) were found in the green alga H. pluvialis and its mutant E1. It is notable that the mutant E1 is found to have considerably higher amounts of total astaxanthin (30.9 mg/g) as compared to the wild strain of H. pluvialis (16.1 mg/g). This indicates that UV-irradiation and EMS compound mutagenesis with subsequent screening using nicotine is an effective method for breeding of a high-producing astaxanthin strain of H. pluvialis. In addition, the green alga C. zofingiensis had a remarkably higher percentage of astaxanthin diesters (76.3% of total astaxanthins) and a remarkably lower percentage of astaxanthin monoesters (18.0% of total astaxanthins) in comparison with H. pluvialis (35.5% for diesters and 60.9% for monoesters), the mutant E1 (49.1% and 48.1%) and Chlorococcum sp. (18.0% and 58.6%).

Optimization of conditions for cell cultivation of Porphyra haitanensis conchocelis in a bubble-column bioreactor

Process conditions for cell cultures derived from conchocelis of female red macroalga Porphyra haitanensis were optimized in an illuminated 0.3-l bubble-column photobioreactor, using CO2 in air as the sole carbon source during a 20-day cultivation period. It reached the highest growth rate when the initial cell density was 700 mg l(-1)(dry weight), the optional aeration rate was 1.2 v/v/min, inorganic nitrate concentration was 15 mM and inorganic phosphate concentration was 0.6 mM. This is the first reported bioreactor cultivation study of cell cultures derived from conchocelis of Porphyra haitanensis.

Analysis of carbohydrates in a tibetan medicine using new labeling reagent, 1-(2-naphthyl)-3-methyl-5-pyrazolone, by HPLC with DAD detection and ESI-MS identification

A new labeling reagent, 1-(2-naphthyl)-3-methyl-5-pyrazolone (NMP), coupling with liquid chromatography (LC) with electrospray ionization mass spectrometry (ESI-MS) for the detection of carbohydrates from a famous Tibetan medicine is reported. Carbohydrates were derivatized to their bis-NMP-labeled derivatives. The method, in conjunction with a gradient elution, offered a baseline resolution of carbohydrate derivatives on a reversed phase Hypersil ODS-2 column. The carbohydrates such as mannose, galacturonic acid, glucuronic acid, rhamnose, glucose, galactose, xylose, arabinose, and fucose could be successfully detected by UV and ESI-MS. Derivatives showed intense protonated molecular ion at m/z [M+H]+ in positive ion mode. The mass to charge ratios of characteristic fragment ions at m/z 473.0 could be used for the accurately qualitative identification of carbohydrates; this characteristic fragment ion was from the cleavage of C2-C3 bond in the carbohydrate chain giving the specific fragment ions at m/z [MH-CmH2m+1Om-H2O](+) for pentose, hexose, and glyceraldehydes, and at m/z [MH-CmH2m-1Om+1-H2O](+) for alduronic acids, such as galacturonic acid and glucuronic acid (m=n-2, n is carbon atom number of carbohydrate). Compared with the traditional 1-phenyl-3-methyl-5-pyrazolone (PMP) reagent, currently synthesized NMP show the advantage of higher sensitivity to carbohydrate compounds with UV and ESI-MS detection.

LC determination of amino acids in rat plasma with fluorescence detection: Application to exercise physiology

An LC method for the determination of 20 amino acids (AAs), using 1,2-Benzo-3,4-dihydrocarbazole-9-ethyl chloroformate (BCEOC) as fluorescent labeling reagent, has been validated and applied for the analysis of AAs in rat plasma at three different states concerning exercise physiology. Identification of AA derivatives was carried out by LC-MS with electrospray ion (ESI), and the MS-MS cleavage mode of the representative tyrosine (Tyr) derivative was analyzed. Gradient elution on a Hypersil BDS C-18 column gave good separation of the derivatives. Excellent linear responses were observed and good compositional data could be obtained from as little as 50-200 mu L of plasma samples. The contents of 20 AAs in rat plasma of three groups (24 rats, group A: quiet state, group B: at exercising exhaust, group C: 12 h after exercising exhaust) exhibited evident difference corresponding to the physiological states. Facile BCEOC derivatization coupled with LC-FLD-ESI-MS analysis allowed the development of a highly sensitive method for the quantitative analysis of trace level of AAs from plasma or other biochemical samples.

Determination of free fatty acids in bryophyte plants and soil by HPLC with fluorescence detection and identification by online MS

A method for the determination of long and short chain free fatty acids (FFAs), using 1-[2-(ptoluenesulfonate)-ethyll-2-phenylimidazole-[4,5-f-9,10-phenanthrene (TSPP) as labeling reagent, has been developed. Identification of FFA derivatives was carried out by HPLC-MS with atmospheric pressure chemical ionization (APCI) in positive ion mode. Gradient elution on an Agilent Eclipse XDB-C-8 column gave good separation of the derivatives. Excellent linear responses were observed and good compositional data could be obtained from as little as 200 mg of bryophyte plants and soil samples. Facile TSPP derivatization coupled with HPLC-APCI-MS analysis allowed the development of a highly sensitive method for the quantitative analysis of trace level of FFAs from biological and natural environmental samples.

Mass spectrometric identification of multihydroxy phenolic compounds in Tibetan herbal medicines

A highly selective and accurate method based on derivatization with dansyl chloride coupled with liquid chromatography-mass spectrometry has been developed for identification of natural pharmacologically active phenolic compounds in extracts of Lomatogonium rotatum plants (Tibetan herbal medicine) obtained by solid-phase extraction. The number of hydroxyl groups on the dansylated phenols was estimated by LC-MS-MS analysis in positive-ion mode. Dansyl derivatization of the compounds introduced basic secondary nitrogen into the phenolic core structures and this was readily ionized when acidic HPLC mobile phases were used. MS fragmentation of the derivatives generated intense protonated molecular ions of m/z [MH](+) (phenol aglycones were transformed into the corresponding free phenols by cleavage of an aglycone bond). Collision-induced dissociation of the protonated molecule generated characteristic product ions of m/z 234 and 171 corresponding to the protonated 5-(dimethylamino)naphthalene sulfoxide and 5 -(dimethylamino) naphthalene moieties, respectively. Selected reaction monitoring based on the m/z [MH](+) to 234 and 171 transitions was highly specific for these phenolic compounds. Characteristic ions with m/z values of [MH - 234](+), [MH 2 x 234](+), and [MH - 3 x 234](+) were of great importance for estimation of the presence of multihydroxyl groups on the phenolic backbone.