恒电流库仑分析法测定乙烯基三乙氧基硅烷

建立了恒电流库仑分析法测定乙烯基三乙氧基硅烷(VTES)含量的方法. 探讨了电解液、反应时间、极化电位、溶剂等因素对测定的影响. 结果表明, 选用V(甲酸)∶V(KBr (2 mol/L))∶V(乙醇)＝6∶1∶3为电解液, 极化电位为200 mV, VTES与溴的四氯化碳溶液反应30 min, 甲醇为VTES的溶剂时测定结果最佳. 该方法用于样品VTES的测定, 加标回收率为98.4%～102.7%, 相对标准偏差为1.7%.     

Isotope gas analysis of tritium-labelled water by means of an automatic apparatus

A procedure and an automatic apparatus designed for the radioactivity measurement of tritium-labelled water in the gaseous phase are described. The method is based on the conversion of water to hydrogen, methane and carbon monoxide in a carbon-packed quartz reactor. The reaction products are swept by hydrogen carrier gas into a piston-type counter tube. Methane is fed to the radioactive gaseous mixture, and the radioactivity of the hydrogen-methane-carbon monoxide mixture is measured in the limited proportional region. The radioactivity values are correlated with the weight of the sample taken and the results are corrected for the ‘memory effect’ obtained in the measurement of inactive water samples. The standard deviation of the procedure, characteristic of its reproducibility, is lower than ±0.5% rel. at preset number of counts.     

Microcomputer-controlled automatic titrator with analysis of results by means of spline functions

A method of controlling an automatic titrator by means of a microcomputer is described. Experimental titration data have been analysed by the use of approximative or rational spline functions.     

Investigation of thermal decomposition reactions by means of thermal analysis and dielectric constant measurement

Dielectric constant measurements as a function of temperature and thermal analysis were performed in copper sulphate pentahydrate and sodium nitrite to study the nature of the decomposition reactions. The application of these combined techniques to the study of several possible mechanisms of thermal decomposition is advanced.     

Narrow span coulometric analysis of neptunium

A narrow span (E _o ±0.1 V) controlled potential coulometric method has been developed for the determination of neptunium in 1M H₂SO₄ with a RSD of 0.2%. The main advantage of this method over the existing coulometric methods is that it can tolerate up to a 5-fold excess of plutonium. The method involves carrying out the electrolysis to about 97% and calculating by an iterative computation the formal electrode potential in situ, which is used to calculate the total amount present in the sample. The method consists in oxidation of all the neptunium to Np (VI) by Ce(IV), destruction of excess Ce(IV) and reduction of Np(VI) to Np(V) by NaNO₂, destruction of excess nitrite by sulfamic acid followed by coulometric titration of Np(V) to Np(VI).     

A sensitive and accurate automatic coulometric detector system for enzymatically produced carbon dioxide

A system for the determination of carbon dioxide liberated in an enzyme reactor is described. The properties of the system are illustrated by the determination of urea. Enzymatically generated carbon dioxide is expelled by boiling, dried and determined coulometrically. The lowest concentration of urea which can be determined with a relative standard deviation of 5% is 1 μM. Compared with other methods based on immobilized enzymes for the determination of compounds as carbon dioxide, this sensitivity constitutes an improvement of about two orders of magnitude. Possible application to sea water is discussed.     

Flow-through coulometric stripping analysis and the determination of manganese by cathodic stripping voltammetry

A simple flow-through system is described for collection of liquid samples into a closed loop. This arrangement can be used for coulometric determinations by the stripping method without previous calibration. The usefulness of the system is demonstrated on the determination of manganese (ca. 10^-6 M) in acetate buffer by cathodic stripping voltammetry.     

Investigation of the thermal decomposition of some periodates by means of emanation thermal analysis (ETA) and DTA

Thermal decomposition of Be₃(IO₅)₂ · 12H₂O, Mg₂I₂O₉ · 11H₂O, Ca₂I₂O₉ · 9H₂O and Ba₂I₂O₉ · 9H₂O in the temperature interval of 20 to 600° was studied by means of emanation thermal analysis (ETA) and differential thermal analysis (DTA). The magnetic properties of decomposition intermediates of periodates studied are discussed.     

Total sulphur analysis in geological and biological materials by coulometric titration following combustion

Summary A simple and rapid procedure for the determination of sulphur in geological and biological samples by combustion in an oxygen current followed by coulometric titration of the sulphur dioxide produced is described. Samples analysed include rocks, soils, sediments, ores, minerals and plants. 8-Hydroxyquinoline is used to remove interfering halogens from the combustion products. 100 mg of sample are mixed with 500 mg of V₂O₅ (oxidant) and 500 mg of Fe (flux) and ignited for 4–15 min in a resistance-type furnace at 1400° C. The method is applicable to sulphur contents in samples of 10 ppm to X0 wt.-% S with standard deviations ranging from 0.001–0.2% S. For testing accuracy 21 standard reference samples were analysed. Results obtained compare favourably with recent publications.

---

Bestimmung des Gesamt-Schwefels in geologischen und biologischen Substanzen durch coulometrische Titration nach vorhergehender Verbrennung der Probe

Zusammenfassung Es wird eine einfache und schnelle Methode der Schwefelbestimmung in geologischen und biologischen Proben durch Verbrennung im Sauerstoffstrom und anschließende coulometrische Titration des freigesetzten SO₂ beschrieben. Es wurden Gesteine, Böden, Sedimente, Erze, Minerale und Pflanzen analysiert. 100 mg der Probe werden mit 500 mg V₂O₅ (Oxidationsmittel) und 500 mg Fe (Fluß-mittel) in 4–15 min in einem Widerstandsofen bei 1400° C verbrannt. Zur Entfernung von Halogenwasserstoffen aus dem Reaktionsgas wird eine 8-Hydroxychinolin-Falle verwendet. Die Methode ist auf Proben mit Schwefelgehalten von 10 ppm bis X0 Gew.-% anwendbar. Die Standardabweichung liegt im Bereich von 0.001–0.2% S. Es wurden 21 Standardproben analysiert, um die Genauigkeit des Verfahrens zu überprüfen. Die Ergebnisse zeigen eine befriedigende Übereinstimmung mit neueren Literaturdaten.

     

Sulfur speciation in hard coal by means of a thermal decomposition method

A new method for the determination of organic and pyritic sulfur in hard coal is presented. The method is based on controlled thermal decomposition of coal sample in oxygen-free and oxygen atmospheres. The results for sulfur liberated in an argon atmosphere at temperatures up to 773 K were close to organic sulfur contents (Sorg), although owing to the definition of 'organic sulfur' the values were not directly comparable. Sorg contents are calculated from the difference between total sulfur content in coal and contents of this element in the form of sulfides, sulfates and pyrites. Sulfur contents, found in the second stage of analysis, were close to pyritic sulfur contents. The difference between total sulfur content and the sum of sulfur values obtained in stages I and II corresponded to sulfur contents in those samples which were neither decomposed nor oxidized at temperatures up to 1173 K. Although not comparable with such conventional concepts for industrial purposes these data are attractive due to the ease and rapidity of the new method for the control of sulfur streams in industrial processes.     

Evaluation of certified reference materials for oxidation-reduction titration by precise coulometric titration and volumetric analysis

The accuracy and uncertainty of coulometric titration of Japanese certified reference materials (CRMs) for oxidation-reduction titration were examined in this study. The results for potassium dichromate, sodium oxalate, and potassium iodate are presented. Potassium dichromate was directly determined by coulometric titration, and sodium oxalate and potassium iodate were determined by volumetric analysis using potassium dichromate assigned by coulometry.The uncertainty of the method was investigated by examining the dependency on the sample size and on the electrolysis current. Changes in the titration parameters did not result in any significant effects on the titration results. The coulometric system used primarily consists of a constant current source, timer, switching circuit, indicator unit, and voltmeter. They were controlled using the coulometry software by a PC/AT compatible computer. A highly automated coulometric system achieves repeatabilities of less than one part in 30,000 (k = 2) and uncertainties of less than one part in 15,000 (k = 2). In addition, using volumetric method, SI units traceable sodium oxalate and potassium iodate (purity standards for redox reaction) CRMs were developed.Reference materials for volumetric analysis are the most basic substances used in analytical chemistry. These materials are analyzed by several analytical methods and are produced globally; however, their purities have not been compared at the international level. Therefore, the relationship between the purity and reliability of these materials has not yet been established. In this paper, we determine the relationship between these parameters by titrating each material obtained from different laboratories.     

Determination of protonation constants by coulometric titration

Application of coulometric titration to the determination of the protonation constants of acids and bases offers several advantages because of its simplicity, precision and accuracy. This procedure is rapid and requires only one calibration solution of strong acid in the same solvent and at the same ionic strength as the solution of acid (or base) being investigated. The procedure seems to be especially advantageous in the case of non-aqueous or mixed solvents having amphiprotic character. The validity of the method has been checked with several substances in water, 95% ethanol and ethylene glycol.     

Investigations of the thermal decomposition of polyvinyl chloride by means of gas chromatography

Gas chromatographic analysis was performed on the products of thermal decomposition of polyvinyl chloride with particular attention on the identification of the obtained reaction products and the role of oxygen in the process.     

Thermal decomposition of copper(II) and zinc carbonate hydroxides by means of TG-MS

Summary For the quantitative analyses of evolved CO₂and H₂O during the thermal decomposition of solids, calibration curves, i.e. the amounts of evolved gases vs. the corresponding peak areas of mass chromatograms measured by TG-MS, were plotted as referenced by the reaction stoichiometry of the thermal decomposition of sodium hydrogencarbonate NaHCO₃. The accuracy and reliability of the quantitative analyses of the evolved CO₂and H₂O based on the calibration curves were evaluated by applying the calibration curves to the mass chromatograms for the thermal decompositions of copper(II) and zinc carbonate hydroxides. It was indicated from the observed ratio of evolved CO₂and H₂O that the compositions of copper(II) and zinc carbonate hydroxides examined in this study correspond to mineral malachite, Cu₂CO₃(OH)₂, and hydrozincate, Zn₅(CO₃)₂(OH)₆, respectively. Reliability of the present analytical procedure was confirmed by the fairly good agreement of the mass fraction of the evolved gases calculated from the analytical values with the total mass-loss during the thermal decompositions measured by TG.     

Solid sampling analysis by means of autoprobe-GFAAS

Summary A recently developed solid sampling graphite system for automatic probe atomisation (SAP-GFAAS) was applied for the direct determination of Pb and Cd in untreated bovine liver matrix.The study was based on 30 livers with a low content of lead (0.045 to 0.27 g Pb/g fresh matter) and of cadmium (0.031–0.24 g Cd/g fresh matter). The basic comparative data for the evaluation of the SAP-GFAAS method were supplied by a standardized GFAAS method with preliminary sample homogenization and matrix decomposition. Additionally, data were obtained by two further solid sampling methods: a front entry graphite system with direct Zeeman effect background correction and a side entry graphite system with high-energy deuterium continuum background correction. The combination of the autoprobe technique and solid sampling was shown to provide analytical results — in terms of handling, accuracy and precision — comparable to those obtained by means of the conventional solid sampling systems. Differences between the results of the sample decomposition method and the solid sampling methods, as well as between the three solid sampling methods must be regarded as being of no practical significance. Part I: see [1].     

非水库仑滴定法测定碳

1引言碳（碳酸盐）的测定曾做过广泛研究，其中，非水库仑滴定测碳因其滴定效率高，稳定性好被列入ＡＳＴＭＤ－５１３－８２；该方法推荐使用美国库仑公司的专利仪器及电解液，其关键技术是非水电解液。本文对该方法的电解液进行了组分选择及优化，建立起完整的测定装置，取得了较好的结果；可作为测定金属含碳量、水体中溶解无机碳的首选方法，广泛应用于冶金、环保等领域。2实验部分2．１仪器与试剂ＫＬＴ－１型库仑仪（江苏电分析仪器厂）；ＰＨＳ－２型酸度毫伏计（上海雷磁仪器厂）。试剂：二甲亚砜、乙醇胺、四乙墓滨化胺为分析纯；…     

Characterization of differently bound water by means of the constants of thermal decomposition kinetics

Summary Compounds containing differently strong bound water molecules were investigated by thermogravimetry and derivative thermogravimetry. The following models were used: inorganic adsorbents, salts containing water of crystallization and a compound with structural water. The temperature interval, the stoichiometry of the water release were determined and kinetic parameters of the processes were calculated. These results could be brought into connection with the nature of the adsorption and crystallization water.

---

Charakterisierung von verschieden gebundenem Wasser mit Hilfe der kinetischen Konstanten der thermischen Zersetzung

Zusammenfassung Thermogravimetrisch und durch derivative Thermogravinietrie wurden Verbindungen untersucht, die mit verschiedener Stärke gebundene Wassermoleküle enthalten: anorganische und organische Adsorbentien, Kristallwasser enthaltende Salze und Verbindungen mit Strukturwasser. Die Temperaturgebiete sowie die Stöchiometrie der Wasserfreisetzung wurden bestimmt und die kinetischen Parameter der Vorgänge ermittelt. Die Ergebnisse ließen sich zu der Natur des adsorptiven oder Kristallwassers in Beziehung bringen.

The authors thank Mr. P. Töke and Mr. M. Matula for running the computer program and Mrs. E. Borsay for the technical assistance.     

Gas-permeation continuous flow coulometric analysis: determination of sulphur dioxide

 A gas permeation system using two gaseous streams flowing on both sides of a membrane is developed. This gas permeation device and a coulometric detector are adapted for the continuous measurement of relatively high concentrations of sulphur dioxide. The interferences of other gases (NO₂, NO and CO₂) can be eliminated by using a scrubber behind the gas permeation device in the acceptor stream. The effects of the donor flow rates and gas pressure as well as the membrane thickness on the signal are discussed. The relative standard deviation is 1.3% (n=7) for 2.002×10^-3 mol/mol certified sulphur dioxide. Received: 19 July 1996/Revised: 22 October 1996/Accepted: 29 October 1996