Accuracy in the precise coulometric titration of ammonia and ammonium ion with electrogenerated hypobromite

A precise and accurate method in which ammonia and ammonium ions are coulometrically titrated with electrogenerated hypobromite was studied. Through the measurement of the current efficiency for generating hypobromite and the dependencies of titration results on electrolysis current and delay time between sampling and starting electrolysis, precision and accuracy of 0.01 and 0.02%, respectively, were obtained. The accuracy of the titration was compared with that of acidimetric coulometric titration of ammonia.     

电位滴定法测定抛光液中的三酸含量

探讨了利用自动电位滴定仪对抛光液中磷酸、硫酸及硝酸的分析方法,以及对溶剂的标定方法。电位滴定法测定三酸,先用硫酸亚铁铵滴定硝酸,再用氢氧化钠滴定磷酸和硫酸,从而计算三酸含量。结果表明,与传统滴定法相比,电位滴定法标定硫酸亚铁铵的相对标准偏差(RSD)从1.1%降至0.13%,标定氢氧化钠的RSD从0.72%降至0.06%。电位滴定法测定自配样品及工厂抛光产品中的硝酸,回收率分别在96%及93%以上。电位滴定法测定自配样品及工厂抛光产品中磷酸和硫酸的回收率偏差在3%以内。手动滴定法测定磷酸和硫酸的回收率偏差在5%~10%,回收效果不如电位滴定法。电位滴定法测定工厂抛光液的三酸加标回收率偏差均小于3%。自动电位滴定法比手工滴定的准确性和精密度明显提高,弥补了手工滴定法只能分析磷酸和硫酸,而无法测定硝酸的缺陷。     

Coulometric titration of acids in isopropanol-I A rapid direct method for the determination of carbon in steel

A new procedure is described for the direct coulometric titration of the carbon dioxide liberated in the high-temperature combustion of steel. The carbon dioxide is absorbed in isopropanol containing 3% of ethanolamine and titrated with 100% titration efficiency with a constant current of 50 mA and spectrophotometric detection of the end-point. The accuracy and precision of the method have been established by the analysis of a wide range of standard steel samples.     

Coulometric titrations with mercury(I) and (II) determinations of secondary amines and mercaptans

A study of the titration of aliphatic amines and mercaptans with electrolytically generated mercury(II) reagent is reported. Amines were titrated after conversion to their corresponding dithio-carbamic acids by reaction with carbon disulfide. Using this procedure, a 3.10^-4F solution of secondary amine was titrated with an accuracy of better than 1% and a concentration of 3.10^-6F with an accuracy of better than 2%. Primary amines constituted an interference in this procedure but were removed prior to the titration with salicylaldehyde. Tertiary amines were found not to interfere. Comparable titrations with generated silver ion did not give quantitative results.The application of electrolytically generated rnercury(II) reagents for the titration of another organic functional group, sulfhydryl, was also studied. The titration of a sulfhydryl compound (cysteine) was studied briefly. Amounts of cysteine down to 1. 29 mg in 100 ml of solution (1.3.10^-4F) were determined with an accuracy of better than 1%. Smaller amounts of cysteine down to 0.26 mg (2.10^-5F) were determined with about 3% accuracy.     

N,N'-disalicylidene-1,3-diaminopropane as a selective chelating titrant for copper(II)

This study was carried out to develop a new complexometric titration method for determination of copper. For this purpose, the standard solutions of copper(II) (10(-3)-10(-5) M) were potentiometrically titrated using N,N'-disalicylidene-1,3-diaminopropane (Schiff base) as titrant and copper(II)-selective electrode for end-point indication in both ammonium acetate and ammonia/ammonium chloride buffer media. The stoichiometry of titration reaction and interference effects of some metal ions on titration of copper were discussed. There was a good agreement between the results obtained by the proposed titration method and ethylenediaminetetraacetic acid (EDTA) titration method. The accuracy and precision of Schiff base method were tested by five replicate determinations both on the standard solution of copper(II) and standard reference materials. The results have indicated that the percentage of copper in alloys can be safely determined by using the Schiff base method without interference from many other metals in alloys.     

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。     

Determination of the composition and the stability constants of complexes of mercury (II) with amino acids

The execution of a titration rarely performed, or of one with a reagent of limited stability, may be facilitated by applying multiparametric curve-fitting to titration-curve data in such a way that the amount of the substance titrated and the concentration of the reagent are evaluated simultaneously; the necessity for prior standardization of the reagent is thereby eliminated. In the potentiometric titration of acetate ion, a very weak base, with unstandardized hydrochloric acid, the accuracy and precision of the concentration of acetate thus obtained are approximately five times better than those which can be secured by titration with standardized acid and location of the point of maximum slope. The accuracy and precision of the concentration of acid are comparable to those that can be secured in very careful standardizations against a primary standard that gives a titration curve of far more favorable shape.     

硫酸铵中氮含量的电位滴定检测

建立一种酸碱电位滴定法直接测定硫酸铵中氮含量的方法。样品溶解后,可直接用氢氧化钠标准滴定溶液进行滴定。为了保证检测的准确度,分别使用硫酸铵高纯试剂和邻苯二甲酸氢钾基准试剂对氢氧化钠标准滴定溶液进行标定,并对标定结果进行比较,两种方法基本无差异。同时,通过适量硫酸的加入避免了样品中游离硫酸对检测结果的影响。该方法检测速度快、检测精度高、绿色环保、易于控制,非常适合于硫酸铵中氮含量的检测。将本方法与蒸馏后滴定法(仲裁法)检测结果进行比较,两种方法无显著性差异。采用本方法测得氮含量的加标回收率为99.9 %-100.3 %,相对标准偏差(RSD,n=5)为0.03 %-0.05 %。分别使用实验方法和蒸馏后滴定法测定不同样品的氮含量,结果相吻合。     

电位滴定法测定火试金得到的金银合粒中的银

本文研究了用自动电位滴定仪测定外购铜物料样品中经火试金熔炼、富集、灰吹后得到的金银合粒中银的方法。金银合粒用硝酸溶解后在自动电位滴定仪上用硫氰酸钾标准溶液滴定银量,选择了仪器的测定条件,考察了溶液酸度、共存元素对测定的干扰。方法相对标准偏差为1.34％～3.62％,测定结果与硫氰酸钾手工滴定法和减杂法相一致。方法的准确度和精密度均能满足分析需要,具有较强的实用性和推广价值。     

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.     

EDTA容量法快速测定酸法生产金属镓的液体物料中镓含量

建立了在酸法生产金属镓过程中,用NH4F掩蔽溶液中的铝,加入过量的EDTA标准溶液使之与镓元素完全络合,调整条件试剂硼酸溶液和无水乙醇的加入量,保证终点的准确判断,过量EDTA以PAN为指示剂用硫酸铜标准溶液回滴求得液体物料中镓含量的分析方法.实验表明,方法的相对标准偏差(RSD)为2.8％～6.5％,加标回收率为97.14％～104.0％.方法有较高的准确性和可靠性,且测定结果精密度高,可实现酸法生产金属镓液体物料中镓含量的快速检测.     

Coulometric titration of acids in non-aqueous solvents

Coulometric titrations of mineral acids, sulphonic acids, carboxylic acids, enols, imides and phenols have been carried out in t-butanol or in acetone with electrically generated tetrabutylammonium hydroxide. Either a potentiometric titration or a visual indicator end-point may be used. The amount of acid titrated ranges from 10 to 60 muequiv, and the precision and accuracy of the method are excellent.     

Modification of iodometric determination of total and reactive sulfide in environmental samples

In iodometric determination of sulfide two reactions are taking place when alkaline solution is added to HCl acid-iodine. The main oxidation reaction (1), H(2)S+I(2)=2HI+S; and side reaction of sulfide (2), S(-2)+4I(2)+8OH(-)=SO(4)(2-)+8I(-)+4H(2)O. Preference of reaction (2) over (1) is dependent on pH increasing to >7. When sulfide solution of pH 9 was mixed with HCl acid-iodine, the recovery exceeded 120%, but the recovery of a solution with a pH of 13 exceeded 200%. To eliminate the side reaction in iodometric titration, the sulfide solution must be acidic when it is mixed with HCl-iodine. To avoid the side reaction (2), the pH of sulfide solutions were adjusted with acetic acid to pH 5.5, mixed with HCl-iodine solution and then titrated with standard thiosulfate with precision and accuracy <+/-3%.     

Rapid determination of the “titration alkalinity” of sea water by equilibration with CO2

Sea-water samples of salinities 31.88, 35.84, and 39.87‰ were acidified and then titrated with HCO₃^- under 1 atm. pressure of CO₂. The resulting pH—HCO₃^- titration plots were interpreted in terms of an ion pairing model, and an equation relating pH and alkalinity was derived. This expression was used to develop a rapid, volume-independent technique to measure alkalinity. The method has an accuracy of ±1% and a precision of ±0.35% (one σ), and lends itself to the analysis of flowing samples and to samples of small volume.     

Coulometric titration of proteins with silver

The sulfhydryl groups of some proteins were studied by a coulometric argentometric titration; disulfide groups in the presence of sulfite were titrated by the same technique. Direct procedures and a technique utilizing excess coulometrically generated silver(I) were used. The latter method enabled small samples (20–1000 μg of protein) to be titrated with a precision of less than 4%. The proteins were generally titrated in both the native state and the denatured state (8 M urea). Bovine serum albumin, α-chymotrypsin, glutathione reductase, human hemoglobin, insulin, β-lactoglobulin, and ovalbumin were examined and the results compared to those of previous workers.     

Determination of traces of zinc by fluorimetrically indicated complexometric titrations

Zinc forms fluorescent complexes with 8-hydroxyquinoline-5-sulphonic acid (HQS) in the pH region 7-10. The stability of these complexes is such that two different titration procedures are possible: the titration of zinc with HQS and the titration of zinc with EDTA in the presence of HQS. For both procedures the choice of the titration conditions is described. Also two separation procedures for zinc are described, especially suitable in connection with the EDTA titration. The practical results show that zinc in concentrations larger than 10(-6)M (0.05 mug/ml) can be titrated with good precision.     

A fast photometric titration for the standardization of dithizone solutions

A simple method is reported for standardizing 10^?5–10^?4 M dithizone solutions for titrimetric analysis. Dithizone in an anhydrous acetic acid/chloroform (4% v/v) medium is titrated with 2 × 10^?4 M mercury(II) acetate in the same medium. The titratioin takes only a few minutes. The accuracy (+0.2%) and precision (r.s.d. = 0.7%) achieved are similar to those obtained by the classical extractive titration with silver(I).     

An automatic back titration method for microchemical analysis

An automatic back titration method for microchemical analysis is introduced, which is based on conventional volumetric analysis's principle and the use of flow injection analysis apparatus for the automation and microminiaturization of the process. The sample and a known, but excess amount of a calibrated reagent solution are injected and propelled into a titration cell, where their reaction takes place. The excess of the reagent is then titrated with a titrant containing an indicator and the end point is monitored photometrically. Since homogeneous mixing in the titration cell is obtained magnetically in the whole process, there is a linear relationship between the analyte's concentration and the volume of the titrant consumed. Nickel in the range of 10-70 g 1(-1) is determined by the above method, in which 30 microl of sample and 500 microl of EDTA are injected and the excess of EDTA is titrated with a standard zinc salt solution containing xylenol orange which could be blocked by nickel ion in a direct titration. This method is characteristic of low sample and reagent consumption, high sampling rate as high as 45 samples h(-1), negligible effect of sample's viscosity, small carry-over effect (lower than 0.14%), and very good precision, whose relative standard deviations are as small as 0.24%.     

Amperometric complex-formation titration of traces of alkaline earths

Alkaline earth metals were determined in microgram quantities by complexometric titration with EDTA, EGTA and DTPA. The end-point was detected by following the anodic wave of the chelating agent at the rotating mercury electrode. All the alkaline earths can be titrated at the microgram level with reasonable accuracy, and calcium may be titrated with EGTA in the presence of a 1000-fold excess of magnesium.