Automatic coulometric method for the determination of carbon and hydrogen in organic substances

Conclusions A coulometric method is proposed for the microdetermination of carbon and hydrogen in organic substances.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 700–701, March, 1972.     

Determination of pentoxifylline in pharmaceutical formulations using iodine as oxidizing agent

Simple, selective and sensitive spectrophotometric methods are described for the determination of pentoxifylline, based on the haloform reaction with a known and excess of standard iodine solution under alkaline conditions. The excess of iodine is determined at pH 3.0 with metol–isoniazid (λ_max=620 nm; method A) or wool fast blue BL (λ_max=540 nm, method B). All the variables have been optimised and the reaction mechanisms presented. Regression analysis of Beer's law plots showed good correlation in the concentration ranges 4.0–24.0 and 0.4–2.4 mg ml⁻¹ for methods A and B respectively. No interferences were observed from excipients and the validity of the methods was tested by analysing pharmaceutical formulations. Recoveries were 99.0–100.0%. The concentration measurements were reproducible within a relative standard deviation of 1.0%.     

A modified method for no carrier added radioiodination of L-tyrosine via chloramine-T as an oxidizing agent

A modified method for the preparation of L-[^131/123I] iodotyrosine as a brain imaging agent is described. The method is based on direct electrophilic radioiodination of L-tyrosine with NaI [^131/123I] using chloramine-T (CAT) and 0.001 g KI as a carrier at pH 7.0. The product was purified by reverse phase high performance liquid chromatography (HPLC). A high radiochemical yield up to 85% of L-[^131/123I] iodotyrosine has been achieved with radiochemical purity of greater than 97%. The relation between the pKa of L-tyrosine and pH of the reaction medium was calculated in order to correlate the radiochemical yield of L-[^131/123I] iodotyrosine and the state of the three ionizable groups of L-tyrosine. Also, the influence of the reaction conditions on the radiochemical yield of L-[^131/123I] iodotyrosine was investigated.     

2-Iodylbenzoic acid as an oxidizing agent for the determination of certain thioxanthene derivatives

An indirect titrimetric method is described for the determination of chlorprothixene, methixene and thiothixene. A known and excessive volume of 2-iodylbenzoate is added and after a specified time the surplus is determined iodometrically. The method has been applied to the analysis of pharmaceutical preparations containing these drugs and the results obtained compare favourably with those from the pharmacopoeial methods. The method is simple, accurate and precise.     

A coulometric method for determining substances that interfere with the measurement of water in oils and other chemicals by the Karl Fischer method

In order to fulfill a need to measure water in crude oils containing materials that interfere with the measurement of water by the Karl Fischer method, by reacting with iodine or iodide, a coulometric method has been developed and validated using 0.1 mol L(-1) Sodium thiosulfate as a calibrant. These interfering substances were measured in water-mass-equivalents, which were expressed as the mass of water that reacts with an equal mass of iodine in the Karl Fischer method. The SO(2)-free reagent that has been modified reacts quantitatively with sodium thiosulfate, cysteine and ascorbic acid but does not react with vinyl acetate. The level of interfering substances was measured in five transformer oils (including Reference Materials RM 8506 and RM 8507), a high and a low sulfur crude oil (Standard Reference Materials SRM 2721 and SRM 2722 respectively), a white oil, a high-vacuum oil and a high-viscosity base-stock oil. One oil contained less than 10 mg kg(-1) (water-mass-equivalents of interfering substances in oil) and two oils (RM 8507 and Drakeol 35) contained no measurable amount of interfering material (<0.2 mg kg(-1)). SRM 2271, a sour crude oil contained 834 mg kg(-1) (standard deviation (SD)=25 mg kg(-1)) (water-mass-equivalents of interfering substances in oil). Approximately 20% of this material was volatile and an additional 20% appeared to undergo some degradation (possibly oxidation) once the oil was exposed to air. These results indicate that this is a general method for measuring substances in oils that react with iodine and that it is capable of measuring in a variety of oils, using commercial instrumentation, interfering substances that inflate water measurements.     

A general method for coulometric titration of alkylanilines with bromine

A general method is described for the coulometric titration of alkylanilines with anodically generated bromine. The reaction is carried out in water-acetic acid medium and the reactivity is governed by varying the water content and the concentration of bromide ion and by the addition of pyridine. In this way most types of alkylanilines can be titrated quantitatively. Unlike the case for alkylphenols, the bromine consumption is not always higher in the pyridine-containing media than in the pyridine-free. The bromine consumption is also more dependent on the bromide content of the medium than it is for alkylphenols. The mean relative error, for the best medium for each compound, is +/-0.9% for primary alkylanilines, +/-0.9% for secondary and +/-1.2% for tertiary.     

A general method for coulometric titration of alkylphenols with bromine

A general method for coulometric titration of alkylphenols with anodically generated bromine is described. The reaction is carried out in a water-acetic acid medium and the reactivity is governed by varying the water content and the concentration of bromide ion and by the addition of pyridine. In that way all types of alkylphenols can be titrated quantitatively. For phenols containing more than one free ortho and para position, the titration can also be carried out either to the monobromination stage or to the full bromination stage. The mean relative error is ± 1·2% for monobromination and ±1·5% for full bromination. A method for rapid determination of the number of free ortho and para positions in alkylphenols by using two coulometric titrations is also described.     

A method for the coulometric determination of the flow rate

Summary A procedure and instrumentation for the continuous determination of the flow rate of measured substances during coulometric titrations are described. This deconvolution method allows to determine the instantaneous concentration value of the sample entering the coulometric cell. The decomposition process (e.g. combustion), which causes this concentration, occurs in a time interval which is much shorter than the time required for the titration itself. This feature makes the method useful for fractional analyses and for on-line measurements.     

钒酸铵氧化-分光光度法测定盐酸氯丙嗪

在磷酸介质中,钒酸铵与盐酸氯丙嗪反应生成红色氧化产物,其最大吸收波长为524nm;据此建立了测定盐酸氯丙嗪含量的钒酸铵氧化-分光光度法,并将其用于直接测定药物制剂中的盐酸氯丙嗪.结果表明,当盐酸氯丙嗪的浓度处于10.0～100mg/L和100～360mg/L范围内时,被测定体系的吸光度与盐酸氯丙嗪的浓度之间呈良好的线性关系;线性回归方程分别为A=-0.061 69+0.010 05c(mg/L,r=0.998 8)、A=0.494+0.004 43c(mg/L,r=0.998 8),检出限为1.96mg/L,相对标准偏差为0.29%,回收率为94.9%～102.9%.     

Synthesis of ferrierite-type zeolite by microwave method using ethylenediamine as an organic structure-directing agent

A new method for the synthesis of ferrierite-type zeolite has been developed using microwave irradiation in the presence of structure-directing agents (templates). The physicochemical characteristics of the synthesized zeolites were investigated by X-ray diffraction analysis, low-temperature nitrogen adsorption–desorption and SEM-EDX. When comparing the synthesis products, it was found that microwave irradiation significantly reduces the crystallization time of the synthesized zeolites compared to traditional hydrothermal treatment     

A validated stability-indicating RP-HPLC assay method for Amsacrine and its related substances

A validated specific stability indicating reversed-phase high-performance liquid chromatography method was developed for the quantitative determination of Amsacrine as well as its related substances determination in bulk samples, in presence of degradation products, and its process related impurities. Forced degradation studies were performed on bulk samples of Amsacrine as per International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human use (ICH) prescribed stress conditions using acid, base, oxidative, thermal stress, and photolytic degradation to show the stability indicating power of the method. Significant degradation was observed during basic hydrolysis, slight degradation was observed in oxidative and thermal stress, and no degradation was observed in other stress conditions. The chromatographic method was optimized using the samples generated from forced degradation studies and the impurity spiked solution. Good resolution between the peaks corresponds to process-related impurities and degradation products from the analyte were achieved on Inertsil ODS column using the mobile phase consists a mixture of 1.0% triethyl amine in 20 mM potassium dihydrogen orthophosphate, with pH adjusted to 6.5, with ortho phosphoric acid in water and acetonitrile using a simple linear gradient. The detection was carried out at wavelength 248 nm. The mass balance in each case was in between 99.4% to 99.9%, indicating that the developed method was stability-indicating. Validation of the developed method was carried out as per ICH requirements. The developed method was found to be suitable to check the quality of bulk samples of Amsacrine at the time of batch release and also during its stability studies.     

Determination of iodine in organic iodine compounds by the non-equilibrium isotopic exchange method

A new type of the isotope exchange method of analysis is proposed. The method can be applied to the exchange system in which the rate of the exchange reaction is rather slow but measurable, before the exchange equilibrium is attained. The validity of the principle of the method is verified experimentally with several exchange systems of RyI+KI^*⇌RyI^*+KI (RyI stands for alkyl, alkylene or benzyl iodide) type. The iodine content of the organic iodine compounds can be determined with an error of ±4%.     

The oxidation of organic substances with compounds of trivalent manganese: XVIII. A contribution to the coulometric generation of manganese(III) acetate in an acetic acid medium

Conditions were found under which manganese(III) acetate can be electrochemically generated at a platinum anode with 100% current efficiency. It was found that even traces of

5. Time Dependence of the Consumption of the Oxidizing Reagent in the Indirect Determination of Hydroquinone with Coulometric Generated Manganese(III) Acetate

     

16.

A new method of accurate pKb determinations for some organic amines     

Zhao‐Kun Jia  Shu‐Fang Zhang  Zheng‐Yu Zhou  An‐Guo Zhang  Rui‐Yan Hou 《International journal of quantum chemistry》2008,108(2):265-271

The accurate pK_b determinations for some amines have been investigated using the combination of the extended clusters‐continuum model with the polarizable continuum solvation model. The formation of molecular clusters by means of the amines wrapped up with water molecules leads to the weakness of the mutual function between the polar solvents and the amines, and, hence, the accuracy of pK_b has been enhanced by using a coherent and well‐defined approach without external approximations or experimental data. The calculations are performed at the HF/6‐311++G(d, p) level and agreed well with experimental data because electron correlation effect cancels mutually in the calculated value of ΔG which is not an absolute value, but a relative value. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

17.

Empirical method for calculation of thermodynamic potentials of organic substances     

Yu. E. Zevatskii  D. V. Samoilov 《Russian Journal of Applied Chemistry》2007,80(2):230-235

A method for establishing relationships between various physicochemical properties of organic substances is developed. The method is based on the concept of linear deviations of physicochemical parameters calculated by additive techniques from experimentally determined values for some broad groups covering various classes of organic substances. The deviations from linearity are analyzed for the example of thermodynamic potentials of 1055 organic substances.     

18.

Iodine trichloride as an analytical reagent for determination of some organic compounds     

Verma KK 《Talanta》1980,27(6):541-544

Procedures are described for the determination of organic compounds with iodine trichloride under Andrews's titration conditions. Samples are directly titrated with iodine trichloride or first reacted with an excess of iodine monochloride, with subsequent titration of the iodine formed. The direct titration is done initially in feebly acid medium, then the acidity is raised (biotin, methionine, cystine and thiomersal). Pre-oxidation with iodine monochloride is used if the organic compound reacts slowly [tryptophan and arsenic(III) compounds] or is determined in bicarbonate medium (hydroxylamine and thiosemicarbazide). The ferrocyanide formed by the reduction of ferricyanide (by thiourea and allylthiourea) can also be titrated. Arsenic(V) compounds are determined after reduction to arsenic(III), and iodine in organic compounds is converted into iodide by alkaline fusion into iodide and the iodide titrated.     

19.

A simple coulometric method for the determination of chloride in natural water     

E Jacobsen  G Tandberg 《Analytica chimica acta》1973,64(2):280-283

     

20.

Applications involving oxidation with ethanolic iodine. Rapid potentiometric method for some reductants     

I. A. Ismail  H. Khalifa  M. Zaky 《Microchemical Journal》1984,30(3):353-357

Rapid potentiometric method was adopted for the determination of small amounts of hexacyanoferrate(II), thiosulfate, thiocyanate, and ascorbic acid, based on oxidation with ethanolic iodine at different pH values and subsequently titration of iodide with mercury(II) using silver amalgam as indicator electrode. The potential breaks at the vicinity of the endpoints were sharp enough for their accurate detection. The method provides for accurate determination of small amounts of some reductants of analytical importance.     

Time (min)	0	5	10	30	60
Consumption of Mn(III) (mol/mol)	2.00	1.99	2.00	2.01	2.00

A new method of accurate pKb determinations for some organic amines

The accurate pK_b determinations for some amines have been investigated using the combination of the extended clusters‐continuum model with the polarizable continuum solvation model. The formation of molecular clusters by means of the amines wrapped up with water molecules leads to the weakness of the mutual function between the polar solvents and the amines, and, hence, the accuracy of pK_b has been enhanced by using a coherent and well‐defined approach without external approximations or experimental data. The calculations are performed at the HF/6‐311++G(d, p) level and agreed well with experimental data because electron correlation effect cancels mutually in the calculated value of ΔG which is not an absolute value, but a relative value. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Empirical method for calculation of thermodynamic potentials of organic substances

A method for establishing relationships between various physicochemical properties of organic substances is developed. The method is based on the concept of linear deviations of physicochemical parameters calculated by additive techniques from experimentally determined values for some broad groups covering various classes of organic substances. The deviations from linearity are analyzed for the example of thermodynamic potentials of 1055 organic substances.     

Iodine trichloride as an analytical reagent for determination of some organic compounds

Procedures are described for the determination of organic compounds with iodine trichloride under Andrews's titration conditions. Samples are directly titrated with iodine trichloride or first reacted with an excess of iodine monochloride, with subsequent titration of the iodine formed. The direct titration is done initially in feebly acid medium, then the acidity is raised (biotin, methionine, cystine and thiomersal). Pre-oxidation with iodine monochloride is used if the organic compound reacts slowly [tryptophan and arsenic(III) compounds] or is determined in bicarbonate medium (hydroxylamine and thiosemicarbazide). The ferrocyanide formed by the reduction of ferricyanide (by thiourea and allylthiourea) can also be titrated. Arsenic(V) compounds are determined after reduction to arsenic(III), and iodine in organic compounds is converted into iodide by alkaline fusion into iodide and the iodide titrated.     

Applications involving oxidation with ethanolic iodine. Rapid potentiometric method for some reductants

Rapid potentiometric method was adopted for the determination of small amounts of hexacyanoferrate(II), thiosulfate, thiocyanate, and ascorbic acid, based on oxidation with ethanolic iodine at different pH values and subsequently titration of iodide with mercury(II) using silver amalgam as indicator electrode. The potential breaks at the vicinity of the endpoints were sharp enough for their accurate detection. The method provides for accurate determination of small amounts of some reductants of analytical importance.