Determination of sulfur in organic compounds using a barium-selective electrode

A procedure was developed for determining sulfur (>1.5 abs %) in sulfur-containing organic compounds. The procedure was based on the combustion of a sample portion in a flask filled with oxygen followed by the potentiometric titration of sulfate ions with barium nitrate in a water-acetone solution. In distinction from analogous procedures, halogens and metals contained in the analyzed compound did not interfere with the determination of sulfur. The error of determination was below 3 rel %.     

Potentiometric microdetermination of aluminium in organic compounds after combustion in a modified oxygen flask

The microdetermination of aluminium in organic compounds by oxygen flask combustion, a simultaneous fusioncombustion procedure was developed, in which the sample in a mixture with KHSO₄ is burnt in a modified oxygen flask under suitable conditions so that the alumina formed is immediately converted into the corresponding water-soluble sulfate. 2.4 ml of 6M HCl are used as absorption solution, in which the combustion residue is completely dissolved by boiling. The solution is then transferred to a titration cell, neutralized with NaOH in the presence of methyl red, and the Al(III) is finally determined in a buffered 40% (V/V) dioxane solution by potentiometric titration with 0.1 M NaF. The results obtained were accurate within ±0.13%; the recoveries of Al are in the range of 99.00 to 99.90%; the standard deviation amounts to 0.06%. The potentiometric titration of Al(III) with fluoride as well as the conditions of the oxygen flask combustion of organic aluminium compounds are discussed.     

Microdetermination of fluorine in organic compounds by oxygen flask combustion and conductometric titration

For the conductometric titration of fluoride with calcium acetate, solvent system in sample solution and titrant, concentration, and acidity of sample solution were examined to establish the titration conditions. Results of these examinations were transferred to the microdetermination of fluorine in organic compounds using oxygen flask combustion method.Comparative examination between quartz and Pyrex flasks for the combustion of fluorine samples indicated that good results were obtained by the use of the former flask, whereas the use of the latter one gave negative values of 1.0–1.6% due to the formation of boron fluoride during the combustion.     

钕量法测定高分子和有机化合物中的磷和氟

本文介绍以Nd(NO_3)_3,为氧瓶燃烧吸收剂,以EDTA回滴过量 Nd~3+ 来测定高分子和有机化合物中磷和氟含量。当化合物中同时含有磷和氟时,先加入浓硝酸煮沸浓缩并蒸干除去F~- 测定 PO_4~3-,然后通过测定磷氟总含量求出氟含量。分解和测定均在普通硬质玻璃氧瓶中进行。测定磷的最大误差为±0.20％,除全氟化合物误差为-0.50％外,氟的测定最大误差为±0.30％。     

Simultaneous microdetermination of iodine and sulfur in organic compounds

A simple and rapid method for the simultaneous microdetermination of iodine and sulfur in organic compounds is described. The procedure utilizes the Schöniger flask method for the combustion, the iodide ions titration with 0.01 N mercuric perchlorate solution and diphenylcarbazone as indicator and the sulfate ions titration with 0.01 M barium perchlorate solution and dimethylsulfonazo III as indicator. The results obtained are in good agreement with calculated values.     

Precise and accurate determination of halogens in organic compounds using an amalgamated gold electrode

Precise and accurate titration of halogens in organic and inorganic materials has been studied. The halogen was titrated with coulometrically generated silver and determined potentiometrically by using an amalgamated gold indicator electrode. An argentometric titration curve using the amalgamated gold indicator electrode showed a large jump in potential at the endpoint as well as in mercurometric determination. Sodium carboxymethyl cellulose (CMC) and aluminum nitrate were added as they are most effective for clarifying the sample solution and eliminating adsorption of the halide ion on the silver halide generated. The electrolytes used were 0.5 M nitric acid containing 0.1% CMC and 0.2 M aluminum nitrate. Approximately 0.2 mmol of chloride, bromide, and iodide ions were titrated with high precision and accuracy. Their standard deviations were 0.03, 0.02, and 0.02%, respectively, with no apparent systematic error. The precise determination of halogens, employing oxygen flask combustion and dissolution of the halide salts in the electrolyte, was carried out with ±0.1% absolute error using samples weighing between 20 and 30 mg.     

Alkalimetry in alcohol-water mixtures with potentiometric end-point detection: Critical remarks on a newer method of European Pharmacopoeia

A new method of the European Pharmacopoeia (Ph. Eur.)—alkalimetry in alcohol-water mixture with potentiometric end-point detection—for the assay of halide salts of alkaloids and other organic N-bases has been investigated using 13 substances. The results were compared to those obtained by nonaqueous direct acidimetry. In general, our measurements show that the Ph. Eur. method may be regarded as an environment-friendly, precise, reproducible approach, with average S.D. ±0.33. However, in six cases out of 13, the method did not work. In these cases, the first inflexion point, which should appear due to the neutralization of a defined, small volume of HCl added to the solution of the sample before the titration, was missing on the potentiometric titration curves. This was observed for papaverine chloride, pilocarpine chloride, pyridoxine chloride, thiamine chloride, histamine dichloride and noscapine chloride; this missing inflexion point hampered the exact measurement of the alkaloid content. This study shows that the method, in the present official form, can be applied only for compounds with pK_a values of seven or higher. For the salts of weaker bases, a modified approach (titration in 70% ethanol, without addition of HCl) is proposed.     

Automatic potentiometric two-phase titration in pharmaceutical analysis : Part 3. Titrimetric Identification of Drugs

The conditional acidity constant in a liquid-liquid two-phase system (pK^*_HA + value) can be used as an identity parameter for drug compounds. The pK^*_HA + value can be calculated if the phase ratio and the acidity and distribution constants are known. Selectivity is obtained mainly by the choice of the organic phase. An excess of hydrochloric acid is first added to the sample in the two-phase system. The hydrochloric acid and the sample are then titrated sequentially with sodium hydroxide. The proposed titration procedure makes it possible to calibrat the electrodes, determine the pK^*_HA + value(s), quantify one or more compounds, and check the performance of the electrodes in one and the same experimental run. Lidocaine was “identified” and assayed in different dosage forms such as ointment and solution for injection. The results were in agreement with those obtained by liquid chromatography.     

oxidmetric titration of triphenyl derivatives of phosphorus,arsenic, antimony and bismuth with N-bromosuccinimide

A simple direct titration for milligram and microgram amounts of triphenylphosphorus, -arsenic, -antimony, and -bismuth is described. The methanolic sample solution, with a little water, hydrochloric acid and bromide added, is titrated with N-bromosuccinimide to a methyl red end-point. All four compounds were titrated in the same way with recoveries of 99–100% and relative standard deviations of 1–5% were obtained.     

A comparison of cationic polymerization and esterification for end-point detection in the catalytic thermometric titration of organic bases

A systematic comparison has been made of two indicator systems for the non-aqueous catalytic thermometric titration of strong and weak organic bases. The indicator reagents, alpha-methylstyrene and mixtures of acetic anhydride and hydroxy compounds, are shown to give results (for 14 representative bases) which do not diner significantly in coefficient of variation or titration error. Calibration graphs for all the samples, in the range 0.01-0.1 meq, are linear, with correlation coefficients of 0.995 or better. Aniline, benzylamine, n-butylamine, morpholine, pyrrole, l-dopa, alpha-methyl-l-dopa, dl-alpha-alanine, dl-leucine and l-cysteine cannot be determined when acetic anhydride is present in the sample solution, but some primary and second amines can. This is explained in terms of rates of acetylation of the amino groups.     

Thermal neutron activation: Sample preparation utilizing graphite as a diluent

A sample preparation method has been developed which produces both standard and unknown samples of the same size, shape, composition and density (a necessary condition for minimum error). A solution of standard or unknown material was pipetted onto graphite wetted with acetone, the material was dried and mixed with additional graphite to give a homogeneous mixture containing≥99% graphite. Portions of the mixture were pressed into uniform cylindrical pellets. Application of the method to the activation analysis of several copper compounds gave results which generally agreed with analysis by thiosulfate titration of liberated iodine to within less than 1%. This work was supported by the United States Atomic Energy Commission.     

Determination of formates by oxidation with iodine

A selective determination of formates based on oxidation with iodine at 100° in presence of potassium hydrogen tartrate, and final titration with thiosulphate solution, is described. The error is below 0.5% for 25–90 mg of formic acid. Few other organic acids interfere.     

The rapid determination of iodine in organic substances

A simple and rapid method for determination of iodine in highly iodized organic substances is described. The method involves oxygen flask combustion of the sample to be analyzed, formation of iodine in a molecular form, and use of a special multicomponent absorption solution containing sodium thiosulfate, phosphate buffer, pH 7.1–7.2, and starch. The quantity of absorbed iodine is determined by iodometric titration of the excess sodium thiosulfate in the absorption solution. The method affords a drastic reduction in the total length of analysis. The relative error of determination is not greater than 1%.     

Automated potentiostatic microdetermination of Cl,Br and I in organic compounds

The automation of a rapid microdetermination of Cl, Br and/or I in organic compounds is described. A combustion furnace, a buret and a titrator are modified and assembled to an apparatus. A solid state programmer using monostable multivibrator circuits to generate various time delays completes a halogen determination automatically in less than 4 min. The following steps in a determination are automated: combustion with sample injection and retraction; feed of reductive flush solution; filling of the titration vessel; titration.Quantitative oxidation of organic samples (about 2–10 mg) in an Ingram-type combustion tube at 1000 °C can be accomplished in two ways: in pure oxygen only or with the aid of an additional layer of a specially prepared $\text{WO}{}_3\text{V}{}_2\text{O}{}_5$ catalyst. A continuously renewed solution of SO₂ or bisulfite assures quantitative reduction to halides. They are flushed into the titration vessel, absorbed in a vigorously stirred absorption solution and titrated immediately with 0.01 N silver nitrate. The titrator is used in potentiostatic mode. End points are set individually for each halogen. Several flush and absorption solutions were investigated and used successfully.     

Optimization of the Micro-Scale Determination of Arsenates by Direct Potentiometric Titration with Silver Ions and its Application to the Determination of Arsenic in-Organic Compounds

Abstract

A micro-scale argentimetric method for the determination of orthoarsenates by potentiometric detection of the end-point has been developed. The optimal results were obtained when this titration was carried out in water-methanol medium, buffered at pH 7.50. This method minimizes the error of old methods arising from the small coprecipitation of silver oxide near the equivalence point and the data obtained are characterized by good accuracy and reproducibility. The procedure to perform the titration with an automatic apparatus is described as well as the optimum concentration range and titration rate. The method was then applied to the determination of arsenic in organic compounds after mineralization in the Schöniger flask using a quartz spiral.     

Complexometric titration of Aluminium

A procedure is given for the complexometric titration of aluminium. A known volume of a standard solution of EDTA is added to the sample solution, and the excess is back-titrated with a zinc sulphate solution, dithizone being used as indicator. The titration is performed at pH = 4.0 — 4.5 and 40 — 50% alcohol is added as solvent for the indicator.The theoretical basis of the method is developed, and the theoretical titration error with various amounts of aluminium and zinc is calculated.The results of some titrations are given.     

Ethyleneglycol-bis(aminoethyl)tetraacetic acid in the amperometric titration of cadmium in the presence of zinc

Cadmium can be titrated amperometrically with EGTA in the presence of zinc; three modifications of the titration are described. The diffusion current of cadmium may be used to follow the titration at —0.90 or —0.70 V vs, the S.C.E, in ammoniacal or acetate-buffered medium respectively The titration may also be performed in ammoniacal solution at —0.30 V vs. the S.C.E., using copper as the amperometric indicator. The influence of iron, aluminium, magnesium, alkaline earths and lead was studied. Ascorbic acid could be used to mask iron and as an effective remover of oxygen. Under appropriate conditions cadmium could be titrated in the presence of 500-fold amounts of zinc. The titration error is approximately 0.002–0.003 ml of a 0.1 M titrant solution.     

库仑滴定法测定有机硅样品中的氮含量

本文利用库仑滴定法研究了高分子和低分子硅氮化合物及含氮有机硅样品中氮含量的测定,并研究和讨论了影响测定结果准确性的因素。     

Atomic absorption spectrometric and potentiometric microdetermination of the nitro and nitroso groups in organic compounds

New simple, rapid, accurate, and selective methods are described for microdetermination of the nitro and nitroso groups in organic compounds. These are based on reduction with cadmium metal and 0.05 M HCl whereby 6 and 4 equivalents of the cadmium ions are released per nitro and nitroso groups, respectively. The cadmium ions are measured by atomic absorption spectrometry at 228.8 nm, potentiometrically by titration with EDTA using the cadmium ion selective electrode, and visually by EDTA titration using Eriochrome Black T indicator. Results with an average recovery of 98% and a mean standard deviation of 1.3% are obtainable and no interferences are caused by many nitrogen, oxygen, and sulfur functional groups.     

Potentiometric Microdetermination of Tungsten in Organic Compounds after Combustion in a Modified Oxygen Flask

A new method for the microdetermination of tungsten in organic compounds such as phosphotungstate and silicotungstate of basic organic compounds is described. The sample is burnt in a modified oxygen flask, the products are absorbed in a sodium hydroxide solution, and complete dissolution of WO₃formed is achieved by boiling the solution for 6–7 min. After removal of carbon dioxide and appropriate pH adjustment, W(VI) is titrated potentiometrically with 10 mMPb(NO₃)₂by using a lead(II) ion-selective electrode as indicator electrode and a double-junction reference electrode. Accurate and precise results are obtained. The absolute error does not exceed 0.14%; the recoveries of tungsten are in the range from 99.74 to 100.00%. The mean relative standard deviation is 0.10%.