Selective masking and demasking for the stepwise complexometric determination of aluminium,lead and zinc from the same solution

Background  

A complexometric method based on selective masking and de-masking has been developed for the rapid determination of aluminium, lead and zinc from the same solution in glass and glass frit samples. The determination is carried out using potassium cyanide to mask zinc, and excess disodium salt of EDTA to mask lead and aluminium. The excess EDTA was titrated with standard Mn(II)SO₄ solution using Erichrome Black-T as the indicator. Subsequently selective de-masking agents – triethanolamine, 2,3-dimercaptopropanol and a formaldehyde/acetone mixture – were used to determine quantities of aluminium, lead and zinc in a stepwise and selective manner.     

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.     

Complexometric Determination of Zinc(II) Using 2,2′-Bipyridyl as Selective Masking Agent

 An indirect complexometric method is described for the determination of zinc(II) using 2,2′-bipyridyl as masking agent. Zinc(II) in a given sample solution is initially complexed with an excess of EDTA and surplus EDTA is titrated with lead nitrate solution at pH 5.0–6.0 (hexamine), using xylenol orange as indicator. An excess of 2,2′-bipyridyl is then added, the mixture shaken well and the EDTA released from the Zn-EDTA complex is titrated with standard lead nitrate solution. Results are obtained for 3–39 mg of Zn with relative errors ≤ 0.5% and standard deviations ± 0.06 mg. The interference of various ions are studied. The method is applied for the determination of zinc in its alloys and ores. Received October 27, 1998. Revision June 10, 1999.     

Complexometric determination of aluminium in iron ore,sinter, concentrates and agglomerates

A method for the complexometric determination of aluminium in iron ore, sinter, concentrates and agglomerates encountered in international trade is described. The sample is fused in a zirconium crucible with a mixed flux of sodium carbonate and sodium peroxide. The fused mass is completely soluble in hydrochloric acid. The R₂O₃ oxides are then precipitated with ammonia and redissolved in hydrochloric acid. Elements such as iron, titanium and zirconium are separated from aluminium by solvent extraction with cupferron and chloroform. After removal of traces of organic matter from the aqueous phase, the solution is treated with an excess of EDTA, which is then back-titrated with zinc solution (Xylenol Orange as indicator). Addition of ammonium fluoride then releases EDTA equivalent to the aluminium and this is titrated with zinc solution. The method is rapid. The precision and accuracy are excellent, and the results comparable with those obtained by the referee method.     

Indirect complexometric determination of palladium usingl-histidine as masking agent

An indirect complexo-titrimetric method is described for the determination of palladium in the presence of other metal ions, L-histidine being used as the masking agent. Palladium(II) and other metal ions are initially complexed with an excess of EDTA and the surplus EDTA titrated with standard zinc sulfate solution at pH 4.5–5.5 using xylenol orange as indicator. An excess of 1 % L-histidine solution is then added, and the released EDTA is titrated with standard zinc sulfate solution. Accurate and reproducible results were obtained for 2–15 mg of Pd with relative errors 0.4% and standard deviations < 0.02mg. Sn(IV) and Au(III) interfere, but can be easily masked. The method is successfully applied for the determination of palladium(II) in alloy compositions.     

Indirect complexometric determination of palladium(II) using sodium nitrite as a selective masking reagent

A selective complexometric method is described for the determination of palladium, sodium nitrite being used as masking reagent. Palladium(II) in a given sample solution is initially cornplexed with an excess of EDTA and the surplus EDTA is titrated with zinc sulfate solution at pH 4.5–5.5 (acetic acid-sodium acetate buffer), using xylenol orange as indicator. An excess of sodium nitrite is then added, the mixture is shaken well and the EDTA released from the Pd-EDTA complex is titrated with a standard zinc sulfate solution. Results are obtained for 2.5–27.5 mg of Pd with relative errors 0.5% and standard deviations 0.05 mg. The interferences of various ions are studied. The method is applied for the determination of palladium(II) in alloys and complexes.     

Selective edta titration of gallium or aluminium in the presence of other metals

The selective determination of aluminium or gallium by EDTA titration is reported. Gallium or aluminium is titrated together with other multivalent ions with EDTA at pH 3-7 and then the pH is raised above 10.5. Aluminates or galliumates are formed with the consequent release of EDTA from the EDTA complexes. The released EDTA is titrated with lead solution using Xylenol Orange as an indicator and with copper using photometric detection of the end-point, for the determination of gallium and aluminium respectively. The theoretical basis of the procedure is discussed.     

Complexometric determination of copper(II) in ores,alloys and complexes using 2-mercaptoethanol as indirect masking reagent

A complexo-titrimetric method for the determination of copper(II) in the presence of other metal ions is described, based on the selective masking ability of 2-mercaptoethanol towards copper(II). Copper and other ions in a given sample solution are initially complexed with an excess of EDTA and the surplus EDTA is titrated with zinc sulfate solution at pH 5.0–6.0 (hexamine), using xylenol orange as indicator. A known excess of 2-mercaptoethanol solution (10%) is then added, the mixture is shaken well and the released EDTA from the Cu-EDTA complex is titrated against standard zinc sulfate solution. The interferences of various ions are studied and the method is applied to the determination of copper in its ores, alloys and complexes. Reproducible and accurate results are obtained for 2.5–40 mg of Cu with relative errors 0.4% and standard deviations 0.04 mg.     

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     

Contributions to the complexometric determination of cation mixtures: Simultaneous titration of iron(iii) and aluminium in the presence of ammonium thiocyanate as indicator

With thiocyanate as indicator iron(III) and aluminium(III) can be titrated simultaneously if [Fe⁺³]/[Al⁺³] ? $\text{1}\text{4}$; iron(III) is titrated directly with EDTA, and aluminium(III) is determined by back-titration of the excess of EDTA with cobalt nitrate solution in an acetone-water medium.     

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.     

An improved selective determination of mercury(II) by complexometric titration

A simple and accurate method has been developed for selective determination of mercury in alkaline solution. It involves the addition of an excess of EDTA to the mercury solution, titration of unreacted EDTA with a standard zinc solution, and then addition of N-allylthiourea solution at pH ? 9. By heating, the mercury-EDTA chelate is decomposed selectively, mercury sulfide is precipitated, and the EDTA freed is again titrated with standard zinc solution. Eriochrome Black T is used as indicator. Interference of some cations is discussed.     

Complexometric determination of cadmium using 2-Mercaptoethanol as masking reagent

A complexometric method for the determination of cadmium(II) in presence of other metal ions is described based on the selective masking ability of 2-mercaptoethanol towards cadmium(II). Cadmium and other ions in a given sample solution are initially complexed with excess of EDTA and the surplus EDTA is titrated with lead nitrate solution at pH 5.0–6.0 (hexamethylentetramine), using xylenol orange as indicator. A known excess of 2-mercaptoethanol solution (10% alcoholic) is then added, the mixture is shaken well and the released EDTA from the Cd-EDTA complex is titrated against standard lead nitrate solution. The interferences of various ions are studied and the method is applied to the determination of cadmium in its complexes. Reproducible and accurate results are obtained for 3.5–25mg of Cd with relative errors 0.65% and standard deviations 0.06 mg.     

Analysis of tellurides of lead and tin by automatic titrations

An analytical method based on automatic potentiometric EDTA and redox titrations was developed for the analysis of tellurides of lead and tin.First, the sum of lead and tin is titrated at pH 4.5 by adding a known excess of EDTA and back-titrating with a standard lead solution. After addition of ammonium fluoride to mask the tin, the EDTA released from the Sn-EDTA complex is titrated with standard lead solution. Alternatively, after the determination of total lead and tin, lead may be determined by back-titration with standard lead on a separate sample aliquot using tartaric acid to mask the tin. Tellurium is separated as tellurous acid, which is then dissolved in a dilute sulfuric acid solution and oxidized by permanganate at room temperature; the excess permanganate is back-titrated with iron(II) solution automatically. This titration may also be used to determine tellurium in the presence of lead and tin after treatment with perchloric acid. Accuracies of 0.1-0.2% can be obtained.     

Analytical aspects of some organic acids

Summary Back titrimetric procedures for the estimation of aluminium, zirconium, and thorium have been developed, which involved the adjustment of the concentration of the metallic salts, concentration of EDTA,ph, and temperature, addition of indicator solution (namely, 2-hydroxy3-naphthoic acid and back titration with standard 0.1 M ferric chloride solution. This method is based on the fact that the excess EDTA, which is added to the metal solutions may be back titrated with iron(III), which forms a highly coloured complex with the indicator, when present in slight excess. Quantities of aluminium, zirconium and thorium as small as 10.8, 4.6, 11.6 mg respectively, can be back titrated with in experimental error, when present in a volume of 100 ml.Part IV: See Z. analyt. Chem. 172, 356 (1960).     

Indirect complexometric determination of cadmium(II) using 1,10-phenanthroline as selective masking agent

An indirect complexometric method is described for the determination of cadmium(II), 1,10-phenanthroline being used as masking agent. Cadmium(II) in a given sample solution is initially complexed with an excess of EDTA and the surplus EDTA is titrated with lead nitrate solution at pH 5.0–6.0 (hexamine), using xylenol orange as indicator. An excess of 1,10-phenanthroline is then added and the EDTA released from the Cd-EDTA complex is titrated with standard lead nitrate solution. Results are obtained for 1.5–57 mg of Cd with relative errors 0.90% and standard deviations 0.06 mg. Cu(II), Co(II), Hg(II), Ni(II), Zn(II), Pd(II), Tl(III), Au(III) and Sn(IV) interfere, but can be easily masked. The method is applied for the determination of cadmium in synthetic alloy solutions.     

Indirect Complexometric Determination of Mercury(II) Using Potassium Bromide as Selective Masking Agent

 A complexometric method for the determination of mercury in presence of other metal ions based on the selective masking ability of potassium bromide towards mercury is described. Mercury(II) present in a given sample solution is first complexed with a known excess of EDTA and the surplus EDTA is titrated against zinc sulfate solution at pH 5–6 using xylenol orange as the indicator. A known excess of 10% solution of potassium bromide is then added and the EDTA released from Hg-EDTA complex is titrated against standard zinc sulfate solution. Reproducible and accurate results are obtained for 8 mg to 250 mg of mercury(II) with a relative error ± 0.28% and standard deviations ≤0.5 mg. The interference of various ions is studied. This method was applied to the determination of mercury(II) in its alloys. Received April 18, 2001 Revision October 10, 2001     

Selective complexometric determination of copper in ores and alloys using 2,2′-bipyridyl as masking agent

An EDTA titration method is described for the determination of copper(II) in the presence of other ions based on the selective masking ability of 2,2′-bipyridyl. Copper and other ions in a given sample solution are initially complexed with an excess of EDTA and the surplus EDTA is titrated with lead nitrate solution at pH 5.0–6.0 (hexamine), using xylenol orange as an indicator. A known excess of 2,2′-bipyridyl solution (1% in 50% alcohol) is then added, the mixture is shaken well and the released EDTA from the Cu–EDTA complex is titrated against standard lead nitrate solution. The interference of various ions are studied and the method is applied to the determination of copper in its ores and alloys. Reproducible and accurate results are obtained for 2.54–25.40 mg of copper with S.D. values <0.04 mg.     

Complexometric determination of palladium(II) using thioacetamide as a selective masking agent

A simple, rapid and accurate complexometric method for the determination of palladium(II) is proposed, based on the selective masking property of thioacetamide towards palladium(II). In the presence of diverse metal ions, palladium(II) is complexed with excess of EDTA and the surplus EDTA is back titrated at pH 5-5.5 (acetic acid-sodium acetate buffer) with standard lead nitrate solution using xylenol orange as indicator. An excess of a 0.5% aqueous solution of thioacetamide is then added to displace EDTA from Pd(II)-EDTA complex. The released EDTA is titrated with the same standard lead nitrate solution as before. Reproducible and accurate results are obtained in the concentration range 0.5 mg - 17.80 mg of palladium with relative error of +/- 0.16% and coefficient of variation not exceeding 0.26%. The effect of diverse ions is studied. The method is used for the determination of palladium in its complexes, catalysts and synthetic alloy mixtures.     

Complexometric titration of thallium(III), by use of 4-amino-5-mercapto-3-propyl-1,2,4-triazole as replacing reagent

A simple and selective EDTA method using a masking and demasking technique is proposed for the determination of thallium(III). The thallium is complexed with excess of EDTA, the surplus being back-titrated (pH 5-6, hexamine buffer) with zinc sulphate solution (Xylenol Orange as indicator). 4-Amino-5-mercapto-3-propyl-1,2,4-triazole is then added and the mixture heated on a water-bath for 5-10 min to displace EDTA from its thallium complex. The EDTA liberated is titrated with zinc sulphate solution. Reproducible and accurate results are obtained in the range 5-75 mg of thallium with both the relative error and coefficient of variation not exceeding 0.4%.