共查询到20条相似文献,搜索用时 15 毫秒
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A sensitive procedure for the determination of sulphide is described. The method depends on the extent to which the iodine-azide reaction has been catalysed by sulphide, and this is measured by titration of the amount of iodine consumed in a fixed time period. 相似文献
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A room temperature photochemically-induced fluorescence (RTPF) method is proposed for the quantitative analysis of seven widely-used chlorophenoxyacid herbicides. The influence of organic solvent, pH (in aqueous solutions), methanol percentage, and UV irradiation time on the excitation and emission wavelengths and fluorescence intensity was investigated. It was found that the largest fluorescence signals were obtained in a mixture of methanol and pH 5 buffer (50/50, v/v), while organic solvents and water produced generally lower signals. The tri- and bichlorinated phenoxyacid herbicides were photolysed significantly more slowly than the monochlorinated derivatives, and the derivatives of 2-propionic acid were photodegraded more quickly than the corresponding derivatives of acetic and butyric acid. Selected UV irradiation times were found to be 15 min for all herbicides under study. Linear calibration graphs were established over about one to two orders of magnitude in the interval 0.1-10 mug ml(-1). The RTPF limits of detection were between 36 ng ml(-1) and 179 ng ml(-1), according to the compound. Analytical application of RTPF to river water samples containing chlorophenoxyacid herbicides is discussed. 相似文献
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A highly precise method is described for the determination of plutonium by constant-current potentiometric titration with primary standard potassium dichromate. The relative standard deviation is 0.04% or better. 相似文献
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M. A. Zaitoun 《Journal of Analytical Chemistry》2006,61(10):1010-1014
A kinetic-spectrophotometric method is proposed to determine glucose in solutions. Measurements were performed at 400 nm;
the negative peak was obtained by subtracting the absorption spectra of myoglobin (Mb) before and after oxidation. In this
method, glucose is added to a mixture of Mb and glucose oxidase. Glucose is oxidized by glucose oxidase and oxygen to gluconate
and hydrogen peroxide is generated. The liberated hydrogen peroxide oxidizes the Mb heme (Fe2+) into Fe3+. The higher the glucose concentration added, the more the H2O2 generation, and the more the Mb oxidation (Fe2+ to Fe3+) and, as a result, the higher the absorbance at 400 nm (negative peak, lower absorbance value). The increments of added glucose
are monitored by measuring the absorbance decay versus time (0–250 s) at 400 nm. Each glucose concentration has an accompanying
unique absorbance value at 250 s. The higher the glucose concentrations, the lower the absorbance at 250 s (measured at 400
nm). The calibration curve for glucose was linear from 0.1 to 3.0 mM; the detection limit was found to be 0.025 mM. There
was no interference from major substances present; the only interference was from species that react with H2O2 (ascorbic acid, uric acid, and urea) or that react with glucose (Cu2+ and Fe3+). Standard deviation in the determination was ±0.01 mM for a 1.3 mM glucose solution (n = 10).
The text was submitted by the author in English. 相似文献
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Sheila Alves Margarida Maria Correia dos Santos Maria Ascensão Trancoso 《Accreditation and quality assurance》2009,14(2):87-93
In this work estimation of measurement uncertainties associated with the total metal content in soils was done by an intralaboratory
approach based on method validation and quality control data, and using two certified reference materials (CRM). CRM and soil
samples were analyzed following procedures based on the methods that are applied to silicate materials. All elements were
determined by atomic absorption spectrometry following a quality assurance program previously established. Quality control
actions were implemented in order to provide reliable data. The precision under within-laboratory reproducibility conditions
was estimated from triplicate analysis. The trueness component was determined as recovery of the analyte from CRMs: soil sample,
SO-2 and river clay sediment, LGC 6139. Combined measurement uncertainty was expressed in terms of precision and recovery
uncertainties and the later further split on CRM replicate analysis and uncertainty of the certified value components. The
results obtained are critically discussed on the basis of the different contributions. For the selection of the reference
material, the CRM dependent terms are critically compared in order to fulfill specific requirements.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
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Automatic equipment is used to generate tin hydride from sample solutions prepared by fusion of powdered rock with lithium metaborate followed by digestion with hydrofluoric and sulfuric acids. The evolved hydride is swept by argon into an electrically heated quartz tube atomizer. The atomic absorption of tin is measured at 224.6 nm. Oxalic acid and 1,10-phenanthroline are used to minimize interferences from iron, copper, and nickel. The detection limit of tin in the rock samples is 0.5 ppm. Results for reference rock samples agree closely with published values. A direct acid digestion procedure produces similar results for tin in many samples. 相似文献
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硫在作物生长过程中必不可少的营养元素之一,主要参与作物生理代谢及生长发育。因此,土壤中硫的含量一直是人们关注的热点,快速准确的检测方法也成为人们研究土壤中硫的关键。在高温燃烧碘量法测定土壤硫含量中,碘酸钾溶液滴定亚硫酸时,对于低含量样品,滴定终点的判断较为困难。通过大量的试验,采用硫代硫酸钠滴定吸收器中反应后剩余的碘酸钾溶液,滴定终点由蓝色消失为无色。终点便于肉眼的观察,提高了分析结果的准确性和再现性;采用EXCEL中的LINEST函数回归标准物质滴定校准工作曲线,方法简便快速。通过国家一级标准物质的分析验证,方法准确度高、精密度好,适用于大批量土壤样品中低含量硫的测定。 相似文献
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A knowledge of the sugar content of molasses is of commercial importance to a number of industrial fermentations. Hence the feasibility of using a glucose oxidase biosensor to determine the glucose content of molasses samples was investigated. This method was compared with standard high-performance liquid chromatographic (HPLC) and gas-liquid chromatographic (GLC) procedures and with the use of a commercially available glucose analyser. A good correlation was obtained between the standard acetic anhydride GLC and glucose oxidase biosensor results (correlation coefficient = 0.98). Rapid and accurate measurements could be carried out using the biosensor without the need to employ the sample preparation step required in standard GLC methods. It was concluded that the use of the biosensor technique for the determination of glucose in molasses samples has distinct advantages over conventional methods. 相似文献
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A flow injection analysis (FIA) catalytic spectrophotometric method for the determination of dissolved iron in seawater was further developed to yield a more sensitive assay with a low detection limit. The method employs an initial sample acidification step followed by an iron pre-concentration step involving an in-line 8-hydroxy-quinoline (8-HQ) metal-chelating resin column. The copper capacity and elution efficiency, as well as the iron FIA performance of three trace-metal clean resins were compared, resulting in the selection of a clean silica gel support for the 8-HQ ligand. The concentrated sample is eluted from the resin with an acidic carrier and mixed with reagents, initiating an iron-catalyzed, color-forming reaction. Increasing the reaction temperature from 18 to 30 °C doubled the sensitivity; reaction temperature control was necessary to obtain good reproducibility in the field. Reagent blanks were as low as 0.05 nM and a detection limit of 0.016 nM was obtained from three times the S.D. of a 0.06 nM seawater sample repeated six times. A 0.06 nM detection limit was calculated from shipboard experiments where total dissolved iron was determined for 10 different samples from the same station. The instrumental sensitivity and precision evolved to the point where the blank associated with the technique is the major factor influencing its detection limit. 相似文献