The semi-micro determination of fluorine,chlorine, and nitrogen in organic compounds: The use of cation exchange resins

The organic compounds are fused in a nickel bomb with sodium in the usual way. If no oxygen is present, the nitrogen is determined as cyanide by Deniges' method. After destruction of cyanide with formaldehyde the total chloride and fluoride is determined by passing the solution through a cation exchange column and determining total acidity in the eluate. The chloride in the same or a separate eluate is then determined by treatment with mercuric oxycyanide or by titration with silver nitrate.     

Gravimetric semi-micro determination of sulphur in organic compounds containing phosphorus

Summary A semi-micro method is described for the determination of sulphur in organic compounds. The sample is burned by the oxygen flask method. After the combustion products are absorbed, the sulphur content is determined gravimetrically as barium sulphate. By increasing the acidity of the solution to 0.20–0.25N in hydrochloric acid, the sulphur content can be determined with the same precision in samples which also contain phosphorus.

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Zusammenfassung Eine Halbmikromethode zur Bestimmung des Schwefelgehaltes in organischen Verbindungen wurde beschrieben. Die Substanz wird nachSchöniger in einem 500-ml-Kolben verbrannt. Nach Absorption der Verbrennungsprodukte wird das Sulfat mit Bariumchlorid gefällt und gewogen. Durch Erhöhung der Salzsäurekonzentration auf 0,20 bis 0,25 Val pro Liter kann der Schwefelgehalt auch in Phosphor enthaltenden Proben mit gleicher Genauigkeit bestimmt werden.

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Résumé On décrit une méthode semi-micro pour le dosage du soufre dans les composés organiques. On brûle l'échantillon suivant la méthode de la fiole à oxygène. Après absorption des produits de combustion, on détermine la teneur en soufre par gravimétrie à l'état de sulfate de baryum. En augmentant l'acidité de la solution jusqu'à 0,20–0,25N dans l'acide chlorhydrique, on peut déterminer la teneur en soufre avec la même précision dans les échantillons contenant également du phosphore.

     

Reversible indicators for use in potassium bromate titrations

A review has been given of reversible indicators for use in bromate titrations. An examination has been made of four reversible indicators, α-naphthoflavone, p-ethoxy-chrysoidine. fuchsin and apomorphine.' All four indicators are satisfactory, but α-naphtho-flavone gives the sharpest end-points. Fuchsin and p-cthoxychrysoidine are gradually destroyed when the end-point is passed and re-passed several times. Apomorphine is only suitable for the titration of trivalent antimony and the end-point is the least sharp of all four indicators.Only α-naphthoflavone is suitable for the titration of 8-hydroxyquinoline solutions. Although it is possible to titrate directly and even back-titrate with standard 8-hydroxyquinoline, the method is not suitable because of the slow reaction between bromine and 8-hydroxyquinoline. The titration can be carried out satisfactorily, however, by adding excess bromate, then excess arsenite and re-titrating with bromate. The other two indicators are not suitable for this purpose; in the direct titration they tend to be destroyed by prolonged contact wth the excess bromine which is always present and, in any case, their colours are obscured by that of the 8-hydroxyquinoline so that the back-titration method is unsatisfactory.Aluminium can be determined satisfactorily after precipitations as the 8-hydroxyquinolate by titration with bromate and arsenite using α-naphthoflavone as indicator.     

Determination of thiocyanate by potassium bromate

Summary Estimation of thiocyanate, based on its titration with standard KBrO₃ solution in presence of 1.5–3.0 N hydrochloric acid, is described. The end point is determined either potentiometrically or with methyl orange as indicator.Sincere thanks of the author are due to Professor S. S. Joshi for research facilities.     

Spectrophotometric determination of trace nitrite based on catalytic oxidation of thionine by potassium bromate

A kinetic method for the determination of trace nitrite (7 × 10^?9–1.2 × 10^?6 M) based on its catalytic effect on the reaction between potassium bromate and thionine in strongly acidic media is reported. The reaction is monitored spectrophotometrically by measuring the decreasing colour of thionine at 602 nm by the fixed-time method. At a given time of 5 min at 30°C, the detection limit is 2 × 10^?9 M (0.001 absorbance ratio, b = 1 cm) and the relative standard deviation for 1 × 10^?6 M nitrite is 2.6% (n = 6). The method is free from most interferences, especially from large amounts of nitrate. The procedure was successfully applied to the determination of trace nitrite in natural water and sausage samples without preconcentration and separation.     

Micro and trace determination of oxygen in organic compounds

Samples are pyrolyzed over carbon in helium doped with chloropentane, which enhances the liberation of the oxygen. The carbon monoxide formed is determined by gas chromatography. A modification of a Carlo Erba CHN+O Elemental Analyzer is described, and results of micro and trace determinations in organic and inorganic compounds are reported. Basic reactions in this method for oxygen determination are discussed.     

Effect of metal ions on the determination of semicarbazide hydrochloride with potassium bromate

Semicarbazide can be titrated quantitatively with potassium bromate in the presence of nickel(II), cobalt(III) and manganese(II) but copper(II) causes serious interference. The effects of copper ions on the reaction between potassium bromate and semicarbazide are investigated and the optimum conditions under which the reaction is quantitative are indicated.     

Thermal decomposition of gamma-irradiated potassium bromate by dynamic thermogravimetry

The thermal decomposition of γ-irradiated KBrO₃studied by dynamic thermogravimetry. The reaction order, activation energy, frequency factor and entropy of activation were computed by means of the Coats-Redfern, Freeman-Carroll and modified Horowitz-Metzger methods and were compared with those for the unirradiated salt. Irradiation enhances the decomposition and the effect increases with the irradiation dose. The activation energy is decreased on irradiation. The mechanism for the decomposition of unirradiated and irradiated KBrO₃ follows the Avrami model equation, [1-(1-α)^1/3] = kt, and the rate-controlling process is a phase boundary reaction assuming spherical symmetry.     

溴酸钾氧化酸性铬深蓝动力学光度法测定痕量亚硝酸根

亚硝酸根是环境中重要的污染物之一,是水质、环境、食品等检测的一个重要项目。催化动力学方法测定痕量亚硝酸根已有较多的报道^[1-6],但未见利用酸性铬深蓝指示物质的报道,酸性铬深蓝是一种配位滴定的指示剂。作者发现在稀疏酸介质中,亚硝酸根对溴酸钾氧化酸性铬深蓝褪色反应有灵敏的催化作用,并研究了该指示反应的动力学条件,建立了催化光度法测定亚硝酸根的新方法。该方法灵敏、简便,可用于水、蔬菜中亚硝根的测定。     

Determination of nitrogen by the decomposition of organic compounds with metallic potassium

Summary A micromethod was proposed for the determination of nitrogen in organic compounds, based on the fusion of organic substances with metallic potassium and subsequent complexonometric determination of the cyanide ions in the alkaline melt. The error of the method is +0.3%.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimisheskaya, No. 7, pp. 1262–1264, July, 1965     

The use of electrodialysis to prepare aqueous bread extracts for bromate determination by chemiluminescence

A cleanup procedure based on electrodialysis is described for the preparation of aqueous bread extracts for bromate determination by chemiluminescence. The technique utilizes electrophoresis with 3 chambers separated by semipermeable membranes. The relative merits of reverse osmosis (RO), ultrafiltration, and nanofiltration membranes with various molecular weight cutoffs were evaluated. The best results were obtained with an RO membrane manufactured from thin-film (composite) polysulfone as support for polyamide. A 0.14 M sodium sulfate solution in the center or collection chamber provides optimum conductivity. Aqueous hydroxylamine sulfate (30 mM) was selected for the anode compartment as a reductant for the anode oxidation products. The constant current mode at 150 mA with a potential of ca 100 volts was used. After electrophoretic separation, the bromate concentration in the collection chamber was typically 2 to 3 times greater than the concentration in the bread extract. The chemiluminescent reaction of bromate with sulfite with hydrocortisone as the enhancer was selected for detection of bromate. The emission, with a wavelength maximum at 575 nm, was found to "glow" rather than "flash" after the reagents were mixed; therefore, it was possible to optimize the light collection period. The method was validated with a variety of commercial bread products. White bread, hot dog buns, hamburger rolls, and a multigrain bread from 7 different manufacturers were studied.     

Kinetics and mechanism of oxidation of secondary alcohols by potassium bromate

The oxidation by Br(V) of propan-2-ol follows the rate law (?d[Br(V)]/dt) = k₄ [alcohol][Br(V)][H⁺]². The initial reaction is complicated by the presence of the product bromide ion. The reaction is composed of two second order reactions—the first, a comparatively slow one and the second stage, a faster reaction which is mainly bromine oxidation. The pure bromate oxidation can be followed by the initial addition of mercuric acetate which prevents the accumulation of bromine in the system under these conditions. The reaction rate does not depend on the nature and structure of the alcohol. A mechanism involving a slow rate-determining formation of an alkyl-bromate ester followed by a fast decomposition to the products is in accord with the observed results.     

Spectrophotometric determination of bromate by sequential injection analysis

A simple and rapid on-line spectrophotometric method for the determination of bromate is proposed. The method is based on the reaction of bromate and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-bromo-PADAP) with SCN⁻, a red complex is formed and monitored at 550 nm. The linear range found is between 0.18 and 3.00 mg l⁻¹ with a detection limit of 0.15 mg l⁻¹. The sampling rate was calculated to be 45 samples per hour. The proposed method has a precision of less than 0.8%.     

Gasometric determination of nitrogen in organic substances

Summary A modification of the Dumas-Pregle micromethod has been developed, permitting the determination of nitrogen in simple and difficultly liquefied organic compounds, thanks to me use of preliminary pyrolysis for decomposing the sample. The accuracy of the method is 0.1–0.2%. Duration of the determination is 20–25 min.The work was begun under the supervision of M. O. Korshun.     

Fluorimetric determination of bromate by ion-exchange separation and post-column derivatization

For the determination of bromate in drinking water a stopped-flow post-column reaction was developed following the separation of bromate from the matrix by an anion-exchange column. In the post-column reaction the analyte was used to oxidize the azo dye sulfonaphtholazoresorcinol, SNAR, and the residual amount was converted into a fluorescent binuclear complex by an excess of gallium ions. The fluorescence was monitored at 585 nm, with a maximum excitation wavelength at 521 nm. The determination of bromate is based on the decrease of the fluorescence intensity with increasing bromate concentration. The given hydrodynamic parameters and the condition of equal flow rates of the two branch streams at each T-piece have to be considered as an important criterion for the experimental set-up. The volume flows and the concentrations required for the reagent solutions in the influent of each T-piece were determined as a result of batch experiments and theoretical considerations. The limit of detection was 0.28 g L^–1bromate for the flow method, which shows linearity up to 15 gL^–1 bromate.     

乙基橙-溴酸钾体系动力学光度法测定痕量甲醛

研究了在稀H2SO4介质中,痕量甲醛催化KBrO3氧化乙基橙褪色反应的适宜条件和影响因素,建立了测定痕量甲醛的动力学光度法。方法采用固定时间法于507 nm波长处测量体系的吸光度,在适宜条件下,ΔA与甲醛质量浓度具有良好的线性关系,方法的线性范围为0~0.24 mg/L,检出限为0.004 mg/L。该方法用于饮料、废水和废气中痕量甲醛的测定,测定结果的相对标准偏差RSD≤3%(n=6),回收率为102%。     

The determination of microgram quantities of organic nitrogen

A method is descriibed for the determination of microgram quantities of nitrogen in a wide variety of materials. This method involves the Kjeldahl procedure for the conversion of nitrogen to ammonium or amine sulphate. Digestion of the sample with concentrated sulphuric acid and catalyst, and, if necessary, pretreatment with hydriodic acid and red phosphorus, are followed by steam-distillation into a dilute acid solution. The final determination depends on the reaction of ammonia, in a suitably buffered solution, with sodium hypobromite reagent, and measurement of the excess reagent by titration of the iodine liberated by it from acidified potassium iodide, with a standard $\text{N}\text{500}$ sodium thiosulphate solution, using sodium starch glycollate indicator.Since sample size is relatively unrestricted and the final titration can measure 5 micrograms of nitrogen, the sensitivity of the method is very high.Reference is made to existing sub-micro methodes which, although sensitive, are time-consuming and specific in application.     

Spectrophotometric determination of novalgin in tablets by use of potassium iodate

An indirect colour reaction has been studied for determination of novalgin in tablets. The method is simple, rapid and reproducible with a relative standard deviation of 0.2%. Novalgin is determined spectrophotometrically by means of its colour reaction with potassium iodate. Beer's law is obeyed over the range 1-10 mg of drug. A tentative reaction mechanism has been proposed.