Coulometric assay of the primary standards potassium dichromate and ammonium hexanitratocerate

The high-precision coulometric titration apparatus of Eckfeldt and Shaffer (Leeds & Northrup Company) has been used for the precision assay of two primary standard materials for oxidation-reduction work. The purity found for NBS 136b Potassium Dichromate. 99.975 %, standard deviation 0.002 %, checks the earlier value of Marinenko and Taylor. Ammonium hexanitratocerate, if low in thorium, is also an excellent primary standard, two recent commercial preparations having purities of 99.972 and 99.984%, a higher standard deviation, 0.005 %, reflecting a minor difficulty in end-point detection caused by platinum oxide formation on the indicating electrodes.     

Robust flow-batch coulometric/biamperometric titration system: determination of bromine index and bromine number of petrochemicals

A flow–batch system was constructed and evaluated to perform coulometric titrations with biamperometric end point detection. The flow section of the system is employed for sampling by injecting a sample volume (50–300 μL) in a flow injection-like system. About 1.5 mL of a suitable carrier solution is delivered by a peristaltic pump in order to quantitatively transfer the sample to the system titration cell (2.0 mL total inner volume). The carrier contains the coulometric precursor for the titrant species. The cell contains two pairs of platinum electrodes used for coulometric generation of reagent and biamperometric detection and is actively stirred. The titrant species is generated and the titration is performed by the usual batch procedure with the excess of titrant being detected by biamperometry following the analysis of the titration curve. System operation is computer controlled and all operations are automated, including titration curve analysis and cell cleaning after the titration is ended. The system is characterized by its robustness because its operation does not depend on flow rates, and the work using coulometric methods which generate gases at the counter-electrode is not troublesome. The flow–batch system has been evaluated for determination of bromine index and bromine number (relative to the total reactive olefin content) in petrochemicals according to an ASTM procedure. Typical precision (R.S.D.) is between 0.5 and 6% for different petrochemicals whose bromine number/index vary from 1000 to 10 mg of bromine per 100 g of sample, respectively. Recoveries for standard additions are between 92 and 123% for 10 mg of Br₂ per 100 g increments and 98 to 101% for 100 mg per 100 g increments. Accuracy of the proposed system was evaluated against results obtained by the standard ASTM with no significant difference detected at 95% confidence level.     

Coulometric titration with air transported sample

Air transported samples of a mixture containing the analyte and a supporting electrolyte are consecutively propelled into a microconduit system through a titration cell, a coil and a detector cell. Different amounts of electrochemically generated titrant are obtained in the separate samples while they are passing through the titration cell. Various quantities of the titrant are achieved by changing the duration of the titrant generating process that is done by various time for the sample solution staying in the titration cell (different sample movement rate). The titrated sample is then homogenised in the coil and detected in an electrochemical detector cell that supplies necessary data for the analyte determination. The declared method is experimentally verified on coulometric titration of hydrochloric acid (HCl) with electrogenerated sodium hydroxide and a titration of aniline with bromine generated in a bromide solution.     

Determination of the drug content of pharmaceuticals containing phenothiazine compounds by triangle programmed flow titration

Summary A flow-through triangle programmed coulometric titration technique is worked out for the determination of phenothiazine compounds. The oxidation reaction of phenothiazines with hypobromite ion served as titration reaction. A biamperometric detector cell has been used for following the titration process. The titration technique has been used for the determination of the drug content (average and individual) of chlorpromazine, promethazine, diethazine and trifluoperazine in pharmaceutical preparations. The relative standard deviation was in the range of 2.0 to 3.5%.

---

Bestimmung des Wirkstoffgehaltes von Phenothiazin-haltigen Pharmazeutica mit Hilfe einer Dreieck-programmierten Durchflu\-Titration

     

电生溴库仑滴定法直接测定渣油中硫醚硫的研究

本文提出了在甲苯－冰乙酸－乙醇－ＮａＢｒ电解液中电生溴库仑滴定电位法指示终点直接测定渣油中硫醚硫的新方法。该电解液对渣油样溶解性能好，终点电位突跃大，结果准确。     

Precise coulometric determination of iron in iron ores with electrogenerated manganese(III) fluoride

Iron in Mohr's salt, electrolytic iron and iron ores has been determined by precision coulometric titration with electrolytically generated manganese (III) fluoride, with biamperometric end-point detection. The titration curve indicated the irreversibility of the electrode reaction of manganese(III) fluoride. Total iron in several standard samples of iron ores was determined with standard deviations of about 0.012%.     

Contributions to the theory of catalytic titrations--I: Complexometric catalytic titrations

Complexometric catalytic titrations with both volumetric and coulometric addition of the titrant have been simulated. By taking into consideration the equilibrium concentration of the catalyst during the titration, general mathematical equations have been set up. The influence of several factors on the shape of the simulated catalytic titration curve has been investigated and is discussed. The work also deals with the conditions under which the approximate mathematical expressions (equilibrium concentration of the catalyst being neglected) can be applied to simulate the catalytic titration curves with a satisfactory accuracy.     

Precise coulometric titration of sodium thiosulfate and development of potassium iodate as a redox standard

In this paper, we determine the effective purity of potassium iodate as a redox standard with a certified value linked to the international system of units (SI units). Concentration measurement of sodium thiosulfate solution was performed by precise coulometric titration with electrogenerated iodine, and an assay of potassium iodate was carried out by gravimetric titration based on the reductometric factor of sodium thiosulfate assigned by coulometry. The accuracy of the coulometric titration method was evaluated by examining the current efficiency of iodine electrogeneration, stability of sodium thiosulfate solutions and dependence on the amount of sodium thiosulfate solution used. The measurement procedure for gravimetric titration of potassium iodate with sodium thiosulfate was validated based on determination of a reference material of known purity (potassium dichromate determined by coulometry with electrogenerated ferrous ions) using the same gravimetric method. Solutions of 0.2 and 0.5 mol/L sodium thiosulfate were stable over 17 days without stabilizer. Investigation of the dependency of titration results on the amount of sodium thiosulfate solution used showed no significant effects, no evidence of diffusion of the sample, and no effect of contamination appearing during the experiment. Precise coulometric titration of sodium thiosulfate achieved a relative standard deviation of less than 0.005% under repeating conditions (six measurements). For gravimetric titration, the results obtained for the effective purity of potassium dichromate were sufficiently close to its certified value to allow confirmation of the validity of the gravimetric titration was confirmed. The relative standard deviation of gravimetric titration for potassium iodate was less than 0.011% (nine measurements), and a redox standard with a certified value linked to SI units was developed.     

Coulometric thermometric titration of halides in molten calcium nitrate tetrahydrate

A method for coulometric thermometric precipitation titrations of chloride, bromide and iodide in molten calcium nitrate tetrahydrate at 55 degrees with coulometrically generated silver ions has been developed. The change in temperature during the titration is followed with the aid of a thermistor bridge coupled to a recorder. To minimize the temperature effect of the passage of current through the melt, two thermistors are connected in opposition in the bridge, with one in the anodic and the other in the cathodic cell compartment. Amounts of 62-80 mumole of halide have been determined with relative error below 0.4% and relative standard deviation less than 2.7%. The relative error in determination of 40 mumole of iodide was + 2%.     

Controlled potential coulometric determination of uranium and neptunium in uranium-neptunium alloys

A controlled potential coulometric titration method has been developed for the determination of neptunium and uranium in the presence of each other. The recovery of a neptunium standard in the presence of uranium was 100.02% with a relative standard deviation of 0.13%, and the recovery of a uranium standard in the presence of neptunium was 100.03% with a relative standard deviation of 0.13%.     

Additional results on the value of the faraday

Repetition of the authors' earlier high-precision coulometric titrations of 4-aminopyridine by the hydrazine-platinum anode and back-titration methods, at the National Bureau of Standards, has yielded a new value for the Faraday, almost identical with the earlier value but with lower uncertainty. The earlier value has been recalculated, using a new value for the density of 4-aminopyridine. The weighted average of the new and old values is 96486.57 1972 NBS coulombs per equivalent, the standard deviation of the mean being 0.48 coulombs per equivalent (4.9 ppm).     

多元校正流动注射电位滴定法同时测定苯甲酸和山梨酸

将流动注射应用于酸碱电位滴定分析,建立了一种可同时测定混合有机酸的电位滴定新方法。在该方法中,用氢氧化钠与氯化钾的混合溶液作为滴定剂,在流通池中同时插入pH指示电极和氯离子指示电极,在滴定过程中的任一滴定点,流出液的pH值和酸碱的混合比例可由两个电极的电位测定值同时获得,从而可应用多元校正法由相应的滴定曲线求得混合酸中每一种组分的含量。该方法不仅免去了体积和时间读数,而且减少了试剂和样品的消耗量,分析速度快。应用该方法对混合样品中的苯甲酸和水杨酸进行同时测定,其相对标准偏差分别为0．19％～0．37％,回收率分别为97．3％～102．6％。     

Contributions to the theory of catalytic titrations-II Precipitation and redox catalytic titrations

Precipitation and redox catalytic titration curves, obtained by both volumetric and coulometric addition of the titrant, have been simulated, taking into account the equilibrium concentration of the catalyst during the titration. The influence of several factors on the shape of the simulated catalytic titration curves has been investigated and is discussed in detail. Simulations of the blank titrations have also been made.     

Contributions to the theory of catalytic titrations-III Neutralization catalytic titrations

Neutralization catalytic titrations of weak monoprotic adds and bases with both volumetric and coulometric addition of the titrant (strong base/acid) have been simulated by taking into account the equilibrium concentration of the catalyst during the titration. The influence of several factors on the shape of the simulated catalytic titration curve has been investigated and is discussed.     

Coulometric titration with electrogenerated +2 tin: Determination of iodine,bromine, and various oxidants via iodometry

The use of electrolytically generated +2 tin as a coulometric titrant has been studied. In a 3 to 4M sodium bromide and 0.2N hydrochloric acid solution, containing 0.2M stannie chloride, the generation of stannous ion is 100% efficient up to a current density of 80 mA/cm². With this medium iodine and bromine can be titrated coulometrically with errors of about ±0.3% or less. The titration is well suited for the iodometric determination of strong oxidants. Employing stannous ion and bromine for direct and reverse titrations, quinone and hydroquinone have been titrated.     

High precision automated conductometric titrations with the bipolar pulse technique

An automated conductometric titration system has been designed and investigated. Stepper motor driven burets have been constructed to provide precise delivery of small volumes of titrant. A bipolar pulse conductance instrument of wide dynamic range is briefly reviewed as a tool in conductometric titrations. Several types of titrations have been carried out to investigate the accuracy and reproducibility of this apparatus. The precision for titrant volumes of 40µl is ±0.64% relative standard deviation.     

A coulometric method for the assay of some easily oxidized organic substances with iodine as an oxidizing agent

A coulometric method for the assay of easily oxidized organic substances, using iodine as an oxidizing agent, has been developed. The principle of the method is to oxidize the substance with an excess of iodine in a water-acetic acid medium and then titrate the iodide formed, with anodically generated silver ion. The titration is followed by dead-stop indication using two platinum electrodes. The method has been applied to the assay of dihydric phenols with hydroxyl groups in the ortho or para positions and to the determination of ascorbic acid in various pharmaceutical preparations. The absolute relative error varied between 0.2 and 2.8% for the 8 phenols investigated and the relative standard deviation between 0.2 and 1%. For standard solutions of ascorbic acid the absolute relative error was 0.9% and for the 6 pharmaceutical preparations investigated the relative standard deviation lay in the range 0.3-0.9%. The method is easy to apply and has a number of advantages over current iodimetric methods.     

Coulometric titration of penicillins and penicillamine with mercury(II)

An absolute coulometric method based on the titration of hydrolysed penicillins with coulometrically generated mercury(II) is presented. An amalgamated gold plate is used as anode and the titration is performed in a pH 4.6 acetate buffer solution. The method gives values which deviate by less than 1% from values obtained by other absolute methods. The relative standard deviation for determination of penicillin G is 0.4%. The determinations of penicillamine and mixtures of penicillamine and penicilloate are also reported.     

Determination of some steroidal bases in non-aqueous media by potentiometric titrations at a small constant current

In this work the volumetric and coulometric titrations of some newly synthesized androstene steroidal compounds with pyridine ring are carried out. The titrations were followed potentiometrically at a small constant current using pairs of identical platinum or glassy carbon electrodes, both in presence of quinhydrone. As the titration reagent, in volumetric titrations served 0.01 mol dm^?3 perchloric acid, and in coulometric titrations hydrogen ions were anodically generated in situ from quinhydrone at the platinum electrode. Sodium perchlorate served as the supporting electrolyte.Amounts of 1.18-5.35 mg of the investigated steroidal compounds were determined with a relative standard deviation less than 1.4% at volumetric and 1.2% at coulometric determinations. A negative influence of the supporting electrolyte on magnitude of the signal change in potentiometric determinations was observed. Glassy carbon electrodes are more advantageous over platinum ones.The achieved results are in good agreement with those of catalytic thermometric titrations.     

Coulometric titration of potassium hydrogen phthalate in a non-aqueous solution, with a vitreous carbon anode

A vitreous carbon anode has been used as working electrode in the coulometric titration of potassium hydrogen phthalate in glacial acetic acid-acetic anhydride medium with protous generated electrochemical oxidation of quinol.