Selective complexometric determination of mercury with sulphite as indirect masking reagent

A complexo-titrimetric method for the determination of mercury(II) in the presence of other metal ions is described, based on the selective masking ability of sulphite ion towards Hg(II). Mercury in a given sample solution is initially complexed with a known excess of EDTA and the surplus EDTA titrated with zinc sulphate solution at pH 5.0–6.0 (hexamine), using xylenol orange (or methylthymol blue) as indicator. An excess of solid sodium sulphite is then added to decompose the Hg(II)-EDTA complex and the released EDTA is titrated with standard zinc sulphate solution. Reproducible and accurate results are obtained for 9.9–99 mg Hg with relative errors < 0.35% and standard deviations < 0.05 mg. The effects of various cations and anions are studied.     

Complexometric determination of thallium(III) in pure solution,alloys, and complexes using semicarbazide hydrochloride as a releasing agent

A simple and accurate complexometric method is proposed for the determination of Tl(III) using semicarbazide hydrochloride as a releasing agent. In the presence of diverse metal ions, thallium is complexed first with a known excess of EDTA, and the surplus EDTA is then titrated with standard zinc sulfate at pH 5.0–6.0 (hexamine) using xylenol orange indicator. An excess of 5% aqueous neutral solution of semicarbazide hydrochloride is then added and the released EDTA is titrated against standard zinc sulfate solution. The method works well in the range 2–50 mg of Tl(III) with relative errors < 0.5%, standard deviations 0.05mg and coefficient of variation 0.4%. The method is applied for the determination of thallium content in complexes and alloy compositions     

Precipitation of lead as lead sulphate by destructive oxidation of EDTA

Gravimetric determination of lead (5–100 mg) by homogeneous precipitation of lead sulphate from a solution containing lead(II), EDTA and sulphate by destructive oxidation of EDTA with hydrogen peroxide or sodium bromate is described. Aluminium(III), iron(III), zinc(II), manganese(II), copper(II), nickel(II), tin(II) and antimony(III) do not interfere in the method. The method can successfully be applied to the analysis of type metal.     

Determination of Sulphate by Titrimetric and Colorimetric Measurement of Equivalent Displaced Zinc Ion

Abstract

Two methods are described for the determination of sulphate in the range of 200 μg to 100 mg by dissolving precipitated barium sulphate in excess of EDTA at pH 12.5. A titrimetric procedure involves back titration of excess EDTA with a standard zinc solution, while a complementary spectrophotometric method makes use of the stability of the barium EDTA complex in the presence of an excess of zinc ions; the latter are reacted with zincon and are equivalent to the amount of sulphate present.     

Determination of sulphide, sulphite and thiosulphate with thallic perchlorate or sulphate

Sulphide, sulphite and thiosulphate can be determined separately or in admixture, with thallic perchlorate or sulphate in acid medium. A sample solution is rendered approximately 0.5 M in acid, 5 ml of 0.05 M KI are added and the solution is titrated to a starch end-point with thallium(III) solution. In another method an acid sample solution is titrated with thallium(III) or iodine solution in the presence of indigo carmine indicator. The end-point is improved in the presence of Co(II).     

Amperometry with two polarisable electrodes-XI Determination of bismuth by EDTA titration

Optimum conditions have been found for a highly selective determination of bismuth via EDTA titration with biamperometric indication of the end-point. The influence of the applied potential, pH and stirring on the accuracy and selectivity of the determination has been studied. In a medium of 0.4M nitric acid only high concentrations of iron(III) and copper(II) interfere with the determination of bismuth. Zirconium, thallium(III) and indium interfere even in small concentrations. The average error of the determination of 5-100 mg of bismuth (when titrated with 0.05M EDTA solution) is +/-0-1 % rel. and for the determination of 0.5-10 mg it is +/-0.3% rel. (0.005M EDTA). The method has been verified by the analysis of a Wood's metal of known composition.     

Cyclic flow-injection analysis for the repetitive determination of zinc with 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol and EDTA.

A circulatory flow-injection method (cyclic FIA) for the repetitive determination of zinc has been proposed. The procedure involves the use of 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol (5-Br-PAPS) together with EDTA as a reagent carrier solution, which is recycled in a single-line flow system via a reservoir. The formed 5-Br-PAPS-Zn(II) complex was measured spectrophotometrically at 552 nm, and the signal intensity corresponded to the zinc concentration. After passing through a flow-through cell, the carrier stream then returned to the reservoir, and the main reagent, 5-Br-PAPS, was successfully regenerated by a ligand-exchange reaction with EDTA, allowing the repetitive determination of zinc. The calibration curve for zinc was linear in the concentration range from 0.4 to 10.0 mg dm(-3) with a correlation coefficient of 0.9995 (n = 6). The detection limit of this method was 0.02 mg dm(-3) (S/N= 3). This method allowed as many as 300 repetitive determinations of 2.0 mg dm(-3) zinc solution with only 100 cm3 of the circulating carrier solution, providing a reduction in the consumption of reagents and an elimination of waste, an important approach towards clean chemistry.     

Spectrophotometric determination of bismuth in concentrates and non-ferrous alloys by the iodide method after separations by diethyldithiocarbamate and xanthate extraction

A method for determining 0.0001-1% of bismuth in copper, molybdenum, lead, zinc and nickel sulphide concentrates is described. After sample decomposition, bismuth is separated from matrix and other elements, except lead and thallium(III), by chloroform extraction of its diethyldithiocarbamate complex, pH 11.5-12.0, from a sodium hydroxide medium containing citric acid, tartaric acid, EDTA and potassium cyanide as complexing agents. Following back-extraction of bismuth into 12M hydrochloric acid and reduction of thallium to the univalent state, bismuth is separated from co-extracted lead and thallium by chloroform extraction of its xanthate from a 2.5M hydrochloric acid-tartaric acid-ammonium chloride medium. Bismuth is then determined spectrophotometrically, at 337 or 460 nm, as the iodide. Interference from lead, which is co-extracted in mug-amounts as the xanthate and causes high results at 337 nm, is eliminated by washing the extract with a hydrochloric acid solution of the same composition as the medium used for extraction. The proposed method is also applicable to lead-, tin- and copper-base alloys.     

A contribution to the use of chelating agents in anodic stripping voltammetry

The E(p)/(2), values of the ions Pb(2+), Bi(3+), Cu(2+), Cd(2+), Tl(+) were determined by means of cyclic voltammetry in solutions of acetate and Britton-Robinson buffers and in solutions containing EDTA and DCTA. DCTA was then utilized in the determination of small amounts of bismuth, down to 10(-7)M, in the presence of 10(4) times as much lead, and of traces of thallium down to 5 x 10(-9)M in the presence of 2 x 10(5) times as much cadmium by anodic stripping voltammetry. The precision was good. Further, the trace copper concentration in analytical grade DCTA was determined. A new flow-through vessel for stripping analysis with solution exchange is also described and the reproducibility of results without solution exchange, with manual solution exchange, and with the flow-through vessel is evaluated for a model determination of thallium in a DCTA solution.     

Indirect determination of fluoride by EDTA back-titration of lanthanum

Semimicro to macro amounts of fluoride ion (0.4-100 mg) are determined rapidly and accurately by precipitation with an excess of lanthanum at pH 2.5-2.8 by digestion on a water-bath, cooling to room temperature, addition of excess of EDTA and back-titration of the excess with zinc solution to the Xylenol Orange end-point at ph 5.8-5..9. Large amounts of chloride, acetate and perchlorate, and small amounts of sulphate and silicate do not interfere, but phosphate does. This method is much superior to the usual thorium nitrate titration method and can be applied after preliminary separation of fluorine by steam distillation or pyrolysis.     

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.     

A rapid complexometric scheme for analysis of iron, aluminium, calcium and magnesium in slags

A simple and rapid complexometric method has been developed for the simultaneous determination of iron, aluminium, calcium and magnesium in a single solution in slags. Phosphorous and small amounts of chromium (1.5 mg) and vanadium (1 mg) do not interfere in the titration. Titanium and manganese are suitably masked with lactic acid and tetra sodium pyrophosphate, respectively. In a suitable aliquot, iron is titrated at pH 2 with EDTA, using sulphosalicylic acid as indicator. To this solution, excess disodium 1,2-cyclohexane diamine tetra acetic acid (DCTA) is added and aluminium is titrated by titrating the excess DCTA with standard copper sulphate solution at pH 3.5, using 1-(2-pyridylazo)-2-naphthol (PAN) as an indicator. A known excess of EDTA is added, the pH is raised to 10 and calcium and magnesium are jointly titrated by titrating the excess EDTA with copper sulphate solution, using PAN indicator. The Ca-EDTA complex is demasked with ammonium oxalate at pH 5 and the released EDTA equivalent to calcium is titrated with copper sulphate solution at pH 10 with PAN indicator. Results of analysis compare favourably with certified values and values obtained by standard methods for BCS and other slags. A set of five samples can be analysed for iron, aluminium, calcium and magnesium in four hours as compared to three days by the classical conventional method.     

微分脉冲伏安法测定硫酸锌溶液中铊

研究了微分脉冲伏安法测定复杂硫酸锌溶液体系中的铊。讨论了伏安图的形成、测定底液和pH值的选择。结果表明:在醋酸介质(pH=4.5±0.2)中,加入适量EDTA、聚乙二醇6000和抗坏血酸的测定体系,采用微分脉冲伏安法可直接测定铊。方法检出限为1.0×10-8g/L,千倍浓度的8种阳离子共存或单独存在时均不干扰测定。方法用于湿法炼锌中上清、一段净化后液、二段净化后液、电积新液、电积废液中铊的测定,相对标准偏差RSD分别为1.6%,2.5%,3.3%,8.3%,4.9%,铊加标回收率为98.4%～102.2%。方法灵敏、简单、快速,用来测定湿法炼锌各阶段硫酸锌溶液中的铊,结果满意。     

Extraction separation of thallium (III) from thallium (I) with n-octylaniline

A novel method is developed for the extraction separation of thallium(III) from salicylate medium with n-octylaniline dissolved in toluene as an extractant. The optimum conditions have been determined by making a critical study of weak acid concentration, extractant concentration, period of equilibration and effect of solvent on the equilibria. The thallium (III) from the pregnant organic phase is stripped with acetate buffer solution (pH 4.7) and determined complexometrically with EDTA. The method affords the sequential separation of thallium(III) from thallium(I) and also commonly associated metal ions such as Al(III), Ga(III), In(III), Fe(III), Bi(III), Sb(III) and Pb(II). It is used for analysis of synthetic mixtures of associated metal ions and alloys. The method is highly selective, simple and reproducible. The reaction takes place at room temperature and requires 15-20 min for extraction and determination of thallium(III).     

Square-wave anodic stripping voltammetric determination of thallium(I) at a Nafion/mercury film modified electrode

A Nafion/mercury film electrode (NMFE) was used for the determination of trace thallium(I) in aqueous solutions. Thallium(I) was preconcentrated onto the NMFE from the sample solution containing 0.01 M ethylenediaminetetraacetate (EDTA), and determined by square-wave anodic stripping voltammetry (SWASV). Various factors influencing the determination of thallium(I) were thoroughly investigated. This modified electrode exhibits good resistance to interferences from surface-active compounds. The presence of EDTA effectively eliminated the interferences from metal ions, such as lead(II) and cadmium(II), which are generally considered as the major interferents in the determination of thallium at a mercury electrode. With 2-min preconcentration, linear calibration graphs were obtained over the range 0.05-100 ppb of thallium(I). An even lower detection limit, 0.01 ppb, were achieved with 5-min accumulation. The electrode is easy to prepare and can be readily renewed after each stripping experiment. Applicability of this procedure to various water samples is illustrated.     

Complexometric determination of some toxic mixtures of ions using bromo-cresol orange with visual endpoint indication

A rapid and simple general complexometric method was presented for the determination of lead, cadmium and thallium or mercury or arsenic(V) in laboratory synthesized mixtures similar to those of some ores, minerals and alloys of such metals. The precision and accuracy attainable in successive titrations of Pb(2+), Cd(2+) and Tl(3+) or Hg(2+) or AsO(3-)(4) (As(5+)) with 0.05 and/or 0.01 mol 1(-1) solutions of disodium ethylenediaminetetraacetate (Na(2)EDTA) and standard Pb(NO(3))(2) of the same concentration using Bromo-Cresol Orange (BCO) as a new metallochromic indicator with visual endpoint indication were studied. For the analysis of a three component mixtures of the aforementioned ions, Tl(3+) was at first directly titrated with Na(2)EDTA at pH 0.5-1 (HNO(3)) using BCO as indicator. At the thallium endpoint an excess of Na(2)EDTA was added and the pH was adjusted at pH approximately 4.8 using hexamine-HNO(3) buffer (solution A). The excess EDTA was back-titrated with standard solution of Pb(NO(3))(2). 1,10-Phenanthroline (1,10-phen) was added to release the EDTA combined with Cd(2+), while thiosemicarbazide (TSC) was used to liberate the EDTA from the mercury-EDTA chelate. To determine AsO(3-)(4) ion in such type of mixtures the pH of (solution A) was raised to a value of 10 using ammonia buffer. Excess standard Mg(2+) solution was added and the formed precipitate of MgNH(4)AsO(4) was separated, dissolved and its magnesium content equivalent to AsO(3-)(4) was determined complexometrically using Eriochrome Black-T (EBT) indicator. The interference caused by different anions, cations and organic acids was investigated. A comparison of the indicators BCO and Xylenol Orange (XO) for successive titration of the studied metal ions was carried out. The proposed successive titration method was applied successfully to some real samples of ores, minerals and alloys of the studied metal ions and the results were satisfactory and agreed with those obtained by AAS.     

Komplexometrische Bestimmung von Yttrium und Aluminium in Yttrium-aluminium-granat-Kristallen

Summary A complexometric method is proposed for the determination of Y and Al in Y-Al-garnet crystals. Y is titrated directly with EDTA using xylenol orange as indicator and sulphosalicylic acid as masking agent for Al. The sum of Al and Y is determined by back-titration of excess EDTA with zinc sulphate solution employing dithizone as indicator. Al is calculated from the difference. The standard deviations are 0.16% and 0.02% for Y and Al, respectively.     

Voltammetric determination of heavy metals leached from ceramics

Anodic stripping voltammetry using a mercury film electrode (MFE) and hanging mercury drop electrode (HMDE) was applied for the determination of trace amounts of lead, cadmium, zinc and copper leached from plates by 4% acetic acid standard solution. The use of a MFE, the fast scan rate (1000 mV/s) by DC voltammetry with subtraction of background current allowed to determine low concentrations of heavy metals. The amounts of metals leached from ware were Pb: 0.1 to 25, Cd: 0.015 to 0.44, Zn: 0.07 to 1.06, Cu: 0.14 to 0.40 μg/mL, depending on the kind of plate and manufacture. Determinations of copper and zinc were carried out using the HMDE electrode in the leachate, determination of tin after medium exchange, and thallium after complexing of lead by EDTA. A significant decrease of metals leached during the second leaching and after washing with detergent solution was found for plates with overglaze decoration. Received: 5 November 1997 / Revised: 24 February 1998 / Accepted: 26 February 1998     

Determination of barium in sulphide ores, concentrates and other geological samples by flame atomic-absorption spectrometry

A rapid, precise and selective analytical method has been developed for estimation of barium in geological samples by flame atomic-absorption spectrometry. The method consists of precipitation of barium sulphate with ammonium sulphate, followed by dissolution of the sulphates in EDTA at pH 10. The barium in this solution is measured by AAS with a nitrous oxide-acetylene flame. Appreciable amounts of lead, calcium and strontium can be tolerated in the method, which has been applied for estimation of barium in sulphide ores and concentrates of lead, zinc and copper, and is feasible for estimation of barium from 20.0 ppm to the per cent level in such geological samples.     

Quantitative precipitation of large amounts of sodium as sodium zinc uranyl acetate and its determination by an indirect complexometric method

Up to 40 mg of sodium can be quantitatively precipitated as sodium zinc uranyl acetate if enough reagent of appropriate composition is added to make the concentrations of zinc and uranium in the mother liquor at least 1.25 and 0.14M respectively. In practice, the reagent solution contains 100 g of uranyl acetate and 300 g of zinc acetate per litre and the volume added (ml) must be at least 15 times that of the solution to which it is added or 1.5 times the number of mg of sodium present, whichever is the greater. The triple salt can then be dissolved in water and the zinc selectively titrated with EDTA at pH 5.3, with Xylenol Orange as indicator. The uranium is masked with ammonium fluoride. Most constituents of ceramics and other silicates, including barium, strontium, magnesium, potassium, sulphate, phosphate and arsenate, do not interfere.