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.     

Graphical evaluation of complexometric titration curves

A graphical method, based on logarithmic concentration diagrams, for construction, without any calculations, of complexometric titration curves is examined. The titration curves obtained for different kinds of unidentate, bidentate and quadridentate ligands clearly show why only chelating ligands are usually used in titrimetric analysis. The method has also been applied to two practical cases where unidentate ligands are used: (a) the complexometric determination of mercury(II) with halides and (b) the determination of cyanide with silver, which involves both a complexation and a precipitation system; for this purpose construction of the diagrams for the HgCl(2)/HgCl(+)/Hg(2+) and Ag(CN)(2)(-)/AgCN/CN(-) systems is considered in detail.     

Indirect complexometric titration of sodium and potassium with EDTA

Summary Sodium is precipitated as sodium zinc uranyl acetate, filtered and dissolved in water, and zinc is titrated with EDTA using eriochrome black T as indicator. Potassium is precipitated as potassium sodium cobaltinitrite and dissolved in hot water containing little hydrochloric acid. The blue colored solution produced by cobalt in solution, with ammonium thiocyanate and acetone was titrated with EDTA until colorless. The results are good.The author is grateful to Prof. Philip W. West, Boyd Professor of Chemistry, Louisiana State University, for kindly providing the facilities to carry out the investigation.     

Direct complexometric titration of thorium with versene using SPADNS

Summary The existing volumetric methods for the determination of thorium are indirect and unsatisfactory. A direct titrimetric method for the estimation of thorium has been developed which involves the adjustment ofph, addition of 1 ml. of 0.02% SPADNS indicator, dilution to volume and titration with versene. It is based on the fact that thorium forms a coloured complex with SPADNS and after the bulk of thorium has reacted with versene, the highly coloured thorium- indicator complex is destroyed, marking the end point. Quantity of thorium as small as 5 mg. can be titrated accurately when present in a volume of 50 ml. Determination of thorium can also be made in presence of large amount of iron by adding ascorbic acid prior to the titration. Interferences of various ions have also been studied. The method proposed for thorium is selective and should be of considerable use in many cases.The author's thanks are due to Dr. A. K. Ghosal, Principal Darjeeling Government College, for providing all laboratory facilities and Dr. A. K. Mukherjee, Indian Association for the Cultivation of Science, Calcutta for his kind help in the work.     

The determination of fluoride by titration with calcium chloride

A new method for the determination of fluoride ions is described. Precipitation is effected with an excess of standard calcium chloride and, after standing overnight, the unconsumed calcium ions are back-titrated with ethylenediamine tetra-acetic acid (EDTA) using Eriochrome Black T as indicator. Halides, sulphate, phosphate and arsenate do not interfere under the recommended conditions. The method is applicable over the range 5-65 mg of fluoride ion.     

New masking procedure for selective complexometric determination of copper(II)

A study has been made of a new masking procedure for highly selective complexometric determination of copper(II), based on decomposition of the copper-EDTA complex at pH 5-6. Among the various combinations of masking agents tried, ternary masking mixtures comprising a main complexing agent (thiourea), a reducing agent (ascorbic acid) and an auxiliary complexing agent (thiosemicarbazide or a small amount of 1,10-phenanthroline or 2,2'-dipyridyl) have been found most suitable. An excess of EDTA is added and the surplus EDTA is back-titrated with lead (or zinc) nitrate with Xylenol Orange as indicator (pH 5-6). A masking mixture is then added to decompose the copper-EDTA complex and the liberated EDTA is again back-titrated with lead (or zinc) nitrate. The following cations do not interfere: Ag(+), Hg(2+), Pb(2+), Ni(2+), Bi(3+), As(3+), Al(3+), Sb(3+), Sn(4+), Cd(2+), Co(2+), Cr(3+) and moderate amounts of Fe(3+) and Mn(2+). The notable feature is that consecutive determination of Hg(2+) and Cu(2+) can be conveniently carried out in the presence of other cations.     

Evaluation of the quality of colour changes of complexometric indicators in the titration of copper (II) with EDTA by tristimulus colorimetry

The quality of colour changes of the indicators hematoxylin, 4(2-pyridylazo)resorcinol (PAR), xylenol orange, pyrocatechol violet, chromazurolS and eriochrome cyanineR in the complexometric titration of copper(II) with ethylenediaminetetraacetic acid (EDTA) were studied with the help of tristimulus colorimetry, utilising a comparative study of the parameters SCD (specific colour discrimination), CIE La^*b^* 1976 and LABHNU 1977. Hematoxylin was found to be the best indicator among those studied. A screened indicator, viz. PAR + malachite green (52), was developed to enhance the quality of colour transition at the end-point and the accuracy of the titrimetric determination.     

PAN-6S作络合指示剂连续滴定测定汞和铅的研究

试验研究了pH3.0和pH5.4的介质中,以1 (2 吡啶偶氮) 2 萘酚 6 磺酸(PAN 6S)作为指示剂,以EDTA为滴定剂连续滴定汞和铅,其终点颜色变化敏锐,准确度高。     

A complexometric titration of inorganic sulphate in synthetic detergents

An accurate method for the determination of inorganic sulphate in synthetic detergents has been developed. After addition of a cationic surface-active agent (cetyl pyridinium chloride) to an anionic detergent, sulphate can be determined by means of indirect titration with EDTA, using a mixture of Metalphthalein and Naphthol Green B as indicator.     

Successive complexometric determination of thorium and uranium in sulphuric acid media

A selective analytical extraction method for rapid successive complexometric determination of thorium(IV) and uranium(VI) in sulphuric acid media is described. The method is based on the extraction of thorium and uranium from sulphuric acid media with N-butylaniline or N-benzylaniline in chloroform. Both thorium and uranium are selectively and quantitatively extracted in the presence of ascorbic acid and EDTA. Most cations and anions do not interfere. The reduction of uranium(VI) with sodium dithionite at room temperature is rapid and quantitative and superior to that with ascorbic acid, which reduces uranium(VI) in boiling solution. The method is simple, rapid and accurate, and the experimental conditions are not highly critical.     

Indirect complexometric determination of beryllium

An indirect complexometric method is described for the determination of beryllium, which is selectively precipitated as Be(NH(4))PO(4), then dissolved in HCl, and the solution passed through an ion-exchange column to retain Be and allow PO(4)(3-)to pass through. Phosphate is precipitated as Mg(NH(4))PO(4) and Mg in the precipitate is titrated with EDTA. Be is obtained from the Mg content.     

Indirect complexometric determination of chromate

Chromate is determined indirectly, by precipitation as silver chromate, dissolution of the precipitate in potassium tetracyanonickelate, and titration of the liberated nickel with EDTA, with Murexide as indicator.     

The coulometric titration of bromate with cuprous copper

A coulometric procedure has been developed by which 18 to 240 μg quantities of bromate may be determined to within 0.3 μg. The bromate is allowed to react with bromide in an acid solution and electrolytically generated cuprous copper is used for the titration. A dual platinum electrode indicator system is used in an amperometric end-point procedure     

Fibre-optic titrations-IV Direct complexometric titration of aluminium(III) with DCTA

The end-point of the direct complexometric titration of Al(3+) in pH 4.6 solution can be determined by monitoring the fluorescence intensity of the aluminium-morin complex, by use of a bifurcated fibre-optic light guide. The method allows the determination of aluminium in the 1-800 ppm range with good precision. The procedure is applicable even when the solutions are strongly coloured or turbid, but because of the slow complexation kinetics requires a titration time of about 20 min.     

Spectrophotometric determination of copper with uramyldiacetic acid

A new method for the spectrophotometric determination of copper using uramyldiacetic acid as chromogenic reagent is proposed. The complex is formed in a wide pH range (2.5–9); but in order to avoid the potential conversion of UDA in murexide it is convenient to work at pH < 3: and has a maximum of absorption at 775 nm. Beer's law is obeyed in the interval 20–420 μg of copper(II)/ml. The Ringbom optimal range falls between 70 and 400 μg of copper(II)/ml, with a minimum photometric error of 2.8. The reaction between the metal and the ligand takes place in the ratio 1:1. The method has been applied to the determination of copper in ores with low content of the metal.