Selective, peroxidase substrate based "signal-on" colorimetric assay for the detection of chromium (VI)

Due to the potentially adverse effects of the chromium (VI) on the human health and also on the environment, the quantitative determination of Cr(VI) is of particular interest. This work herein reports a facile, selective and rapid colorimetric determination of Cr(VI) based on the peroxidase substrate-2,2'-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) diammonium salt (ABTS) as the color developing agent. ABTS, which was usually acted as peroxidase substrate for the enzyme linked immunosorbent assay, is used here for the first time to fabricate the "signal-on" colorimetric Assay for Cr(VI).

Capillary electrophoretic analysis of pharmacologically active xanthone compounds from Swertia przewalskii pissjauk extract

Pharmacologically active xanthone compounds isolated from Swertia przewalskii pissjauk were well separated by capillary electrophoresis (CE) within 5 min, using a running buffer of 25 mM disodium tetraborate at pH 9.0. Quantitative determination was shown to be possible because regression equations revealed a linear relationship between the peak area of each constituent and its concentration, with correlation coefficients of 0.9972-0.9994. The relative standard deviations were between 0.44%-0.73% for migration times and 2.52%-4.28% for peak areas. The dissociation constant of 1,7-O-beta-D-glucopyranosyl-8-hydroxy-3,7-dimethoxyxanthone, 1,8-dihydroxy-3, 7-dimethoxy-xanthone and 1,7-dihydroxy-3,8-dimethoxyxanthone were also measured by the CE method, giving a value of 9.04, 8.94, and 8.59, respectively.

Comparison of comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry and gas chromatography-mass spectrometry for the analysis of tobacco essential oils

A sample of tobacco essential oil was analyzed using gas chromatography-mass spectrometry (GUMS)and comprehensive two-dimensional gas chromatography coupled to a time-of-flight mass spectrometry (GC x GC/TOFMS), respectively. In the GUMS analysis, serially coupled columns were used. By comparing the GUMS results with GC x GC/TOFMS result,,, many more components in the essential oil could be found within the two-dimensional separation space of GC x GC. The quantitative determination of components in the essential oil was performed by GC x GC with flame ionization detection (FID), using a method of multiple internal standards calibration, (c) 2005 Elsevier B.V. All rights reserved.

A high throughput Nile red method for quantitative measurement of neutral lipids in microalgae

Isolation of high neutral lipid-containing microalgae is key to the commercial success of microalgae-based biofuel production. The Nile red fluorescence method has been successfully applied to the determination of lipids in certain microalgae, but has been unsuccessful in many others, particularly those with thick, rigid cell walls that prevent the penetration of the fluorescence dye. The conventional "one sample at a time" method was also time-consuming. In this study, the solvent dimethyl sulfoxide (DMSO) was introduced to microalgal samples as the stain carrier at an elevated temperature. The cellular neutral lipids were determined and quantified using a 96-well plate on a fluorescence spectrophotometer with an excitation wavelength of 530 nm and an emission wavelength of 575 run. An optimized procedure yielded a high correlation coefficient (R-2 = 0.998) with the lipid standard triolein and repeated measurements of replicates. Application of the improved method to several green algal strains gave very reproducible results with relative standard errors of 8.5%, 3.9% and 8.6%, 4.5% for repeatability and reproducibility at two concentration levels (2.0 mu g/mL and 20 mu g/mL), respectively. Moreover, the detection and quantification limits of the improved Nile red staining method were 0.8 mu g/mL and 2.0 mu g/mL for the neutral lipid standard triolein, respectively. The modified method and a conventional gravimetric determination method provided similar results on replicate samples. The 96-well plate-based Nile red method can be used as a high throughput technique for rapid screening of a broader spectrum of naturally-occurring and genetically-modified algal strains and mutants for high neutral lipid/oil production. (C) 2009 Published by Elsevier B.V.

Electron ground state energy level determination of ZnSe self-organized quantum dots embedded in ZnS

Optical and electrical characterization of the ZnS self-organized quantum dots (QDs) embedded in ZnS by molecular beam epitaxy have been investigated using photoluminescence (PL), capacitance-voltage (C-V), and deep level transient Fourier spectroscopy (DLTFS) techniques. The temperature dependence of the free exciton emission was employed to clarify the mechanism of the PL thermal quenching processes in the ZnSe QDs. The PL experimental data are well explained by a two-step quenching process. The C-V and DLTFS techniques were used to obtain the quantitative information on the electron thermal emission from the ZnSe QDs. The correlation between the measured electron emission from the ZnSe QDs in the DLTFS and the observed electron accumulation in the C-V measurements was clearly demonstrated. The emission energy for the ground state of the ZnSe QDs was determined to be at about 120 meV below the conduction band edge of the ZnS barrier, which is in good agreement with the thermal activation energy, 130 meV, obtained by fitting the thermal quenching process of the free exciton PL peak. (C) 2003 American Institute of Physics.

X-Ray diffraction determination of the fractions of hexagonal and twinned phases in cubic GaN layers grown on (001)GaAs substrate

Being an established qualitative method for investigating presence of additional phases in single crystal materials, X-ray diffraction has been used widely to characterize their structural qualities and to improve the preparation techniques. Here quantitative X-ray diffraction analysis is described which takes into account diffraction geometry and multiplicity factors. Using double-crystal X-ray four-circle diffractometer, pole figures of cubic (002), {111} and hexagonal {10 (1) over bar0} and reciprocal space mapping were measured to investigate the structural characters of mixed phases and to obtain their diffraction geometry and multiplicity factors. The fractions of cubic twins and hexagonal inclusions were calculated by the integrated intensities of rocking curves of cubic (002), cubic twin {111}, hexagonal {10 (1) over bar0} and hexagonal {10 (1) over bar1}. Without multiplicity factors, the calculated results are portions of mixed phases in only one {111} plane of cubic GaN. Diffraction geometry factor can eliminate the effects of omega and X angles on the irradiated surface areas for different scattered planes. (C) 2001 Elsevier Science B.V. All rights reserved.

Determination of AlxGa1-xAs Auger sensitivity factors

AlxGa1-xAs Auger sensitivity factors have been determined by using PHI610 scanning Auger microprobe with pure elemental standards Al, Ag and matrix GaAs. The quantitative results of AlxGa1-xAs measured by the present method are in very good agreement with X-ray double crystal measurements. it is shown that by using sensitivity factors obtained from the self-instrument, the accuracy of the quantitative AES analysis can be considerably improved compared with that using elemental relative sensitivity factors given by the PHI handbook or internal standard method.

Determination and identification of isoflavonoids in Radix astragali by matrix solid-phase dispersion extraction and high-performance liquid chromatography with photodiode array and mass spectrometric detection

The isoflavonoids in Radix astragali were determined and identified by HPLC-photodiode array detection-MS after extraction employing matrix solid-phase dispersion (MSPD). As a new sample preparation method for R. astragali, the MSPD procedure was optimized, validated and compared with conventional methods including ultrasonic and Soxhlet extraction. The amounts of two major components in this herb, formononetin (6) and ononin (2), were determined based on their authentic standards. Four major isoflavonoids, formononetin (6), ononin (2), calycosin (5) and its glycoside (1), and three minor isoflavonoids, (6aR,11aR)-3-hydroxy-9, 10-dimethoxypterocarpan (7), its glycoside (3), and (3R)-7,2'-dihydroxy-3',4'-dimethoxyisoflavone-7-O-beta-D-glycoside (4), were identified based on their characteristic two-band UV spectra and [M + H](+), [aglycone + H](+) and [A1 + H](+) ions, etc. The combined MSPD and HPLC-DAD-MS method was suitable for quantitative and qualitative determination of the isoflavonoids in R. astragali. (C) 2003 Elsevier B.V. All rights reserved.

Determination of sulfur-containing compounds in diesel oils by comprehensive two-dimensional gas chromatography with a sulfur chemiluminescence detector

This article reports an analytical method for separating, identifying and quantitating sulfur-containing compounds and their groups in diesel oils (170-400degreesC) using comprehensive two-dimensional gas chromatography coupled with a sulfur chemiluminescence detector. The identification of target compounds and their groups was based on standard substances, the group separation feature and the-effect of comprehensive two-dimensional gas chromatography. The quantitative analysis on major sulfur compounds and total sulfur was carried out based on the linear response of sulfur chemiluminescence detector and the internal standards method. The results of total sulfur determination in the samples were compared with those from ASTM D 4294 standard method, the R.S.D. percentage were <6.02%, correctness of this method can meet the industrial requirement. To the end, the method developed was used to investigate the sulfur-containing compounds in different diesel oils, the result shows that the distribution of sulfur-containing compounds in diesel oils from different process units are apparently different. The sulfur compounds in fluid catalytic cracking (FCC), residuum fluid catalytic cracking (RFCC) diesel oils mainly exist in the form of alkyl-substituted dibenzothiophenes that add up to about 40-50% of the total sulfur, while this number is only 6-8 and 20-28% in visbreaking (VB) and delayed-coking (DC) diesel oils, respectively. (C) 2003 Elsevier B.V. All rights reserved.

Determination of photochemically produced hydroxyl radicals in seawater and freshwater

A variety of short-lived, reactive chemical species (i.e. free radicals and excited state species) are known to be photochemically produced in natural waters. Some of these transients may strongly affect chemical and biological processes, and they have been implicated in the degradation of organic pollutants and natural organic compounds in aqueous environments. Previous studies demonstrated that the highly reactive hydroxyl radical (OH) is photochemically formed in seawater. However, the quantitative importance of this key species in the sea has not been previously studied because of past analytical limitations. By using a highly sensitive probe based on α-H atom abstraction from methanol, we were able to measure production rates and steady-state concentrations of photochemically produced OH radicals in coastal and open ocean seawater and freshwaters. The validity of the method was tested by intercalibrating with an independent, OH-specific reaction, hydroxylation of benzoic acid, and also by competition kinetics experiments. Our OH production rates and steady-state concentrations for freshwaters are in excellent agreement with those measured by previous investigators for similar waters. In contrast, for seawater, the values we measured are 1–3 orders of magnitude higher than previously predicted by models, indicating that there is a major unknown photochemical OH source (s) in seawater.

The use of CE-electrochemiluminescence with ionic liquid for the determination of bioactive constituents in Chinese traditional medicine

CE/tris(2,2-bipyridyl) ruthenium(ll) (Ru(bpy)(3)(2+)) electrochemiluminescence (ECL), CEECL, with an ionic liquid (IL) detection system was established for the determination of bioactive constituents in Chinese traditional medicine opium poppy which contain large amounts of coexistent substances. A minimal sample pretreatment which involves a one-step extraction approach avoids both sample loss and environmental pollution. As the nearby hydroxyl groups in some alkaloid such as morphine may react with borate to form complexes and IL, as a high-conductivity additive in running buffer, could cause an enhanced field-amplified effect of electrokinetic injection. Running buffer containing 25 mM borax-8 mM 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF(4)) IL (pH 9.18) was used which resulted in significant changes in separation selectivity and obvious enhancement in ECL intensities for those alkaloids with similar structures. Sensitive detection could be achieved when the distance between the Pt working electrode and the outlet of separation capillary was set at 150 mu m and the stainless steel cannula was fixed approximately 1 cm away from the outlet of the capillary. Quantitative analysis of four alkaloids was achieved at a detection voltage of 1.2 V and a separation voltage of 15 kV in less than 7 min.

Determination of sulpiride by capillary electrophoresis with end-column electrogenerated chemiluminescence detection

Background: Capillary electrophoresis (CE) with tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)(3)(2+)]-electro-generated chemiluminescence (ECL) detection is a promising method for clinical analysis. In this study, a method combining CE with Ru(bpy)(3)(2+) ECL (CE-ECL) detection that can be applied to amine-containing clinical species was developed, and the performance of CE-ECL as a quantitative method for determination of sulpiride in human plasma or urine was evaluated. Methods: Sulpiride was separated by capillary zone electrophoresis in uncoated fused-silica capillaries [510 cm x 25 mum (i.d.)] filled with phosphate buffer (pH 8.0 and a driving voltage of +15 kV, with end-column Ru(bpy)(3)(2+) ECL detection. A platinum disc electrode was used as working electrode. Sulpiride in human plasma or urine samples (100 muL) was extracted by a double-step liquid-liquid extraction procedure, dried under nitrogen at 35 degreesC in a water bath, and reconstituted with 100 muL of filtered water. The extraction solvent was ethyl acetate-dichloromethane (5:1 by volume). Results: Under optimum conditions (pH 8.0 phosphate buffer, injection for 6 s at 10 kV, and +1.2 V as detection potential), separation of sulpiride was accomplished within 4 min. The calibration curve was linear over a concentration range of 0.05-25.0 mumol/L, and the limit of detection was 2.9 x 10(-8) mol/L for sulpiride. Intra- and interday CVs for ECL intensities were <6%. Extraction recoveries of sulpiride were 95.6-101% with CVs of 2.9-6.0%. The method was,clinically validated for patient plasma and urine samples. Conclusions: CE combined with Ru(bpy)(3)(2+) ECL is reproducible, precise, selective, and enables the analysis of sulpiride in human plasma and urine. It thus is of value for rapid and efficient analysis of amine-containing analytes of clinical interest.

Quantitative analysis of pethidine using liquid secondary ion and tandem mass spectrometry

A method for the quantatitive determination of pethidine in human urine by liquid secondary ion and tandem mass spectrometry is presented. Quantification was carried out by using ketamine as internal standard. It was found that the collision-induced dissociation (CID) spectrum of the [M + H](+) ion of pethidine exhibited a prominent daughter ion at mit 220 and ketamine also yielded the same daughter ion at nit 220, For ((quadrupole)) quantitative analysis, the first quadrupole mass filter was set to transmit mit 220 and a narrow-range magnet scan yielded a spectrum of parents, including mit 238 and 248, corresponding to ketamine and pethidine, respectively. Copyright (C) 1999 John Wiley & Sons, Ltd.

Quantitative structure-property relationships for colour reagents and their colour reactions with cerium using computational neural networks

Quantitative structure-activity/property relationships (QSAR/QSPR) studies have been exploited extensively in the designs of drugs and pesticides, but few such studies have been applied to the design of colour reagents. In this work, the topological indices A(x1)-A(x3) suggested in this laboratory were applied to multivariate analysis in structure-property studies. The topological indices of 43 phosphone bisazo derivatives of chromotropic acid were calculated. The structure-property relationships between colour reagents and their colour reactions with cerium were studied using A(x1-Ax3) indices with satisfactory results. The purpose of this work was to establish whether QSAR can be used to predict the contrasts of colour reactions and in the longer term to be a helpful tool in colour reagent design.

EASTMAN-AQ/NIII MODIFIED ELECTRODE CHARACTERIZATION AND APPLICATION IN FLOW-INJECTION DETERMINATION OF CARBOHYDRATES AND AMINO-ACIDS

A novel Eastman-AQ/Ni(II) chemically modified electrode (CME) produced by "double coating step" deposition of a poly(ester sulphonic acid) polymer film and Ni2+-containing crystalline species onto glassy carbon instead of a metallic nickel electrode exhibited stable electrocatalytic oxidation of numerous alpha-hydrogen compounds including carbohydrates, amines and amino acids. In cyclic voltammetry, the electrocatalysis appeared with an irreversible anodic wave at +0.55 V (vs. Ag/AgCl). The CME was adapted for constant-potential amperometric detection of these compounds in flow injection analysis. Using the CME, the linear response concentration range was between 1.0 x 10(-5) and 5.0 x 10(-2) mol/l and the detection limit was 5.0 x 10(-6) mol/l for glucose. The stability of the CME was adequate for routine quantitative application.