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991.
A. Cuesta J.L. Todoli A Canals 《Spectrochimica Acta Part B: Atomic Spectroscopy》1996,51(14):1791-1800
The present paper describes a new flow injection method for the determination of Chemical Oxygen Demand (COD). This method consists of a first digestion step, where the sample is heated by microwave radiation, a second one where an anionic exchange resin retains the Cr(VI) that has not been reduced by the organic matter of the sample and a third one where Cr(VI), after being eluted, is determined by flame atomic absorption spectrometry. The microwave power applied, the sulphuric acid concentration, the liquid flow in the digestion step and the sample volume were the variables studied. The recovery and precision obtained with this method are similar to those obtained using a standard semi-micro method, whereas the throughput is much higher (up to 50 determinations per hour). As regards sensitivity, by changing the sample loop volume and the concentration of dichromate, one can analyze samples with Chemical Oxygen Demand values between 25 and 5000 mg/l. The limit of detection is about 7 mg/l COD. An interesting feature of the new method, which is not shared by most other flow injection methods of Chemical Oxygen Demand determination, is that there is no matrix effect in the determination step. 相似文献
992.
Complex III of the mitochondrial electron transport chain, ubiquinol-cytochrome c reductase, was isolated by blue native polyacrylamide gel electrophoresis. Ten of the 11 polypeptides present in this complex were detected directly by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) following electroelution of the active complex. Tryptic and chymotryptic digestion of the complex permit the identification of specific peptides from all of the protein subunits with 70% coverage of the 250 kDa complex. The mass of all 11 proteins was confirmed by second dimension Tricine sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and elution of the separated polypeptides. Additionally, the identity of the core I, core II, cytochrome c and the Rieske iron-sulfur protein were confirmed by liquid chromatography/tandem mass spectrometry (LC/MS/MS) characterization of the peptides generated by in-gel trypsin digestion of the SDS-PAGE separated proteins. The methodology demonstrated for analyzing this membrane-bound electron transport complex should be applicable to other membrane complexes, particularly the other mitochondrial electron transport complexes. The MS analysis of the peptides obtained by in-gel digestion of the intact complex permits the simultaneous characterization of the native proteins and modifications that contribute to mitochondrial deficits that have been implicated as contributing to pathological conditions. 相似文献
993.
994.
Sajedi RH Naderi-Manesh H Khajeh K Ranjbar B Ghaemi N Naderi-Manesh M 《Applied biochemistry and biotechnology》2004,119(1):41-50
A new α-amylase was extracted from a recently found strain of Bacillus sp. and purified by ion-exchange chromatography. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed a single
band for the purified enzyme with an apparent molecular weight of 59 kDa. The optimum temperature and pH range of the enzyme
were 40–60°C and 4.5–7.5, respectively, and its activation energy was 1.974 kcal/mol. The K
m
value for the enzyme activity on solubie starch was 4 mg/mL, and the T
m
values obtained from the circular dichroism (CD) results of thermal unfolding were 78.7 and 80.2°C in the absence and presence
of the calcium, respectively. The enzyme was almost completely inhibited by the addition of Fe3+, Mn2+, and Zn2+ and was activated by EDTA, Cr3+, and Al3+. Moreover, it was partially inhibited by Ca2+, Ba2+, Ni2+, and Co2+. Proteolytic digestion of the enzyme using trypsin combined with results from T
m
using CD and irreversible thermoinactivation suggests that this enzyme can be considered a moderate thermophile with both
mild flexibility and rigidity. 相似文献
995.
Multi-syringe flow injection system with in-line microwave digestion for the determination of phosphorus 总被引:3,自引:0,他引:3
A multi-syringe system for spectrophotometric determination of total phosphorus involving in-line digestion is proposed. Sample and digestion solution were dispensed and directed towards a digestion vessel located inside a domestic microwave oven (MWO) where sample digestion took place. Afterwards, the digested sample was merged with the necessary reagents for the colorimetric determination based on the molybdenum blue method. Several digestion conditions were studied regarding composition of digestion solution, digestion time and power set on the MWO. The system was applied to waste water samples and results shown a good agreement with the reference method. Repeatable results (R.S.D.<2.41%) and determination frequency of 12 h−1 were obtained. 相似文献
996.
Mustafa Tuzen 《Analytica chimica acta》2004,504(2):325-334
A column solid-phase extraction method for the preconcentration and determination of cadmium(II), copper(II), cobalt(II), iron(III), lead(II), nickel(II) and zinc(II) dithizone chelates by atomic absorption spectrometry has been described. Diaion HP-2MG was used as adsorbent for column studies. The influences of the various analytical parameters including pH of the aqueous solutions, amounts of ligand and resin were investigated for the retentions of the analyte ions. The recovery values are ranged from 95 to 102%. The influences of alkaline and earth alkaline ions were also discussed. The preconcentration factor was 375, when the sample volume and final volume are 750 and 2 ml, respectively. The detection limits of the analyte ions (k=3, N=21) were varying 0.08 μg/l for cadmium to 0.25 μg/l for lead. The relative standard deviations of the determinations at the concentration range of 1.8×10−4 to 4.5×10−5 mmol for the investigated elements were found to be lower than 9%. The proposed solid-phase extraction procedure were applied to the flame atomic absorption spectrometric determinations of analyte ions in natural waters (sea, tap, river), microwave digested samples (milk, red wine and rice) and two different reference standard materials (SRM1515 apple leaves and NRCC-SLRS-4 riverine water). 相似文献
997.
Nikolaos S. Thomaidis Efrosini A. Piperaki Panayotis A. Siskos 《Mikrochimica acta》1995,119(3-4):233-241
A procedure for the determination of the aqua regia soluble content of lead, cadmium and chromium in a sewage sludge reference material (CRM 145R) by electrothermal atomic absorption spectrometry (ETAAS) is described. A comparison of the dissolution procedure proposed in the certification report, to an oven-assisted digestion and a proposed microwave digestion procedure is performed. In the ETAAS method developed, 1 g of Pt proved to be an appropriate modifier for each of the above heavy metals. Possible sources of error at each analytical step are addressed. The metal contents obtained with the proposed method are in a good agreement at 95% significance level with the certified values given for CRM 145R. 相似文献
998.
This paper presents the dynamic behaviour of the anaerobic digestion process, based on a simplified model. The hydraulic,
biological and physicochemical processes such as those which underpin anaerobic digestion have more than one stable stationary
solution and they compete with each other. Further, the attractive domains of the stable solutions vary with the key parameters.
Thus, some initial transient process moving toward one stable solution could suddenly move towards another solution, at which
a so-call catastrophe takes places (e.g. washout). The paper systematically analyses the stationary solutions with their associated
stability, which provides insight and guidance for anaerobic digestion reactor design, operation and control. 相似文献
999.
Éder José dos Santos Amanda Beatriz Herrmann Suzete Kulik de Caires Vera Lúcia Azzolin Frescura Adilson José Curtius 《Spectrochimica Acta Part B: Atomic Spectroscopy》2009
A simple and fast method for the determination of Se in biological samples, including food, by axial view inductively coupled plasma optical emission spectrometry using on-line chemical vapor generation (CVG–ICP OES) is proposed. The concentrations of HCl and NaBH4, used in the chemical vapor generation were optimized by factorial analysis. Six certified materials (non-fat milk powder, lobster hepatopancreas, human hair, whole egg powder, oyster tissue, and lyophilised pig kidney) were treated with 10 mL of aqua regia in a microwave system under reflux for 15 min followed by additional 15 min in an ultrasonic bath. The solutions were transferred to a 100 mL volumetric flask and the final volume was made up with water. The Se was determined directly in these solutions by CVG–ICP OES, using the analytical line at 196.026 nm. Calibration against aqueous standards in 10% v/v aqua regia in the concentration range of 0.5–10.0 µg L− 1 Se(IV) was used for the analysis. The quantification limit, considering a 0.5 g sample weight in a final volume of 100 mL− 1 was 0.10 µg g− 1. The obtained concentration values were in agreement with the total certified concentrations, according to the t-test for a 95% confidence level. 相似文献
1000.
研究了采用ICP-AES技术,快速测定海产品中多种微量元素的方法,各分析元素的相对标准偏差为1.4 ̄6.8%,方法简单、快速、准确度高。 相似文献