Contributions to the basic problems of complexometry--XXII: determination of thorium and scandium in the presence of each other

A new method for the determination of thorium and scandium in the presence of each other is presented. Two aliquots of the solution are necessary. In one the sum of thorium and scandium is determined by direct titration with DCTA. In the second, thorium and scandium are treated with an excess of TTHA, phosphate is added, and zinc is used to titrate the excess of TTHA and to displace the scandium from its TTHA complex.     

Contributions to the basic problems of complexometry--XXIII: determination of thorium, scandium and some lanthanides in the presence of each other

A new method is described for the determination of thorium, scandium, and the sum of light lanthanides, in the presence of each other. The method is based on the titration of thorium plus scandium with DCTA (1,2-diaminocyclohexanetetra-acetic acid) at pH 2.5-3.5, with Xylenol Orange as indicator. After addition of TTHA (triethylenetetraminehexa-acetic acid) the thorium-DCTA complex is converted into the thorium-TTHA complex according to the equation Th-DCTA + TTHA = TH-TTHA + DCTA. Simultaneously, free lanthanum, cerium, praseodymium and neodymium react with TTHA. The excess of TTHA and the liberated DCTA are then determined by titrations with zinc and with lanthanum solutions according to the equations DCTA + TTHA + 3Zn = Zn-DCTA + Zn(2)-TTHA and DCTA + TTHA + 2La = La-DCTA + La-TTHA. From the results, the amounts of thorium and scandium, and the sum of the lanthanide concentrations, can easily be calculated. Further possibilities, e.g., determination of heavier lanthanides, are briefly discussed.     

A note on the determination of thorium in the presence of some bivalent metal ions

A new method for complexometric determination of thorium in the presence of bivalent metals without their masking is presented. Two aliquots of metal solution are necessary. In one the sum of the thorium and other metals is determined by DTPA titration. The second aliquot is treated with Zn(2)TTHA complex. Only thorium, forming a 1:1 complex with TTHA, displaces twice its molar amount of zinc from the complex, while other elements displace only an equimolar amount of zinc. The amount of thorium corresponds to the difference of consumption in the two titrations.     

~1H and ~(13)C NMR studies of TTHA complexes with diamagnetic rare earth ions

TTHA complexes with diamagnetic rare earth ions (La3+, Y3+ and Lu3+) were studied by 1H and 13C NMR spectroscopy. A symmetric structural model was suggested for La(TTHA) complex and an asymmetric model for Y(TTHA) and Lu(TTHA) complexes. The complex formation was dependent on the pH value of the solution. The interactions of La(TTHA) with the additional metal ions (La3+, Y3+ and Ca2+) were relatively weak, but relatively strong for that of Lu(TTHA) with the additional Lu3+.     

Benzohydroxamic acid as a reductometric titrant: Determination of thorium

Milligram quantities of thorium can be accurately determined by precipitating it as oxalate, dissolving the precipitate in 11 sulphuric acid and oxidizing the liberated oxalic acid with a known excess of standard permanganate solution above 60 °C in sulphuric acid medium, and finally estimating the excess permanganate by titrating with a standard solution of benzohydroxamic acid either visually or potentiometrically. 10 mg quantities of thorium has been estimated with an error not exceeding 0.12%. The coefficient of variation for 10 estimations is found to be 0.06% and 0.12% for potentiometric and visual methods, resp.     

Back titration with mercuric nitrate in alkaline medium

Summary A rapid, reliable and accurate method for the determination of trivalent chromium, based on back titrating excess EDTA solutions in the presence of chromium versenate, with mercuric nitrate in alkaline media is given. By its aid amounts of chromium in the order of 50 micro- to 15 milligrams can be determined with fair accuracy. The method is applied for analysis of binary mixtures of chromium with thorium, copper(II), bismuth or mercury(II).     

Construction of 3d-4f mixed-metal complexes based on a binuclear oxovanadium unit: synthesis, crystal structure, EPR, and magnetic properties

The oxovanadium(IV)-lanthanide(III) heteronuclear complexes, [[Ce(H2O)7(VO)(TTHA)0.5][(VO)2(TTHA)]].8H2O (2), [Pr(H2O)7(VO)3(TTHA)1.5].10H2O (3), and [Nd(H2O)7(VO)3(TTHA)(1.5)].10H2O (4) (H6TTHA = triethylenetetraaminehexaacetic acid), were prepared based on a binuclear building block of [(VO)2(TTHA)]2- in [VO(H2O)5][(VO)2TTHA].4H2O (1). The X-ray crystallographic studies show that 1 is an ion-pair complex, containing the [(VO)2(TTHA)]2- unit as a useful building block. Adding the light Ln3+ ions to this synthesis system, three new 3d-4f mixed-metal-based complexes were obtained. Although the light lanthanide ions always exhibit similar chemical behavior, the structures of 2-4 are not homologous. 2 is exhibited as a one-dimensional coordination polymer, comprising an unusual Ce2V2 heterometallic lattice in the chain structure, which is the second report of a oxovanadium(IV)-lanthanide(III) coordination polymer. 3 and 4 are isomorphic, every two of the Ln3+ cations linked three [(VO)2(TTHA)]2- anions, forming an interesting linear octanuclear structure. This kind of heteronuclear linear complex is rather rare, which expands the realm of 3d-4f complexes. Further investigations such as IR spectra, UV-vis spectra, magnetic properties, and EPR spectra were studied, and a detailed discussion is given for this system.     

Titrimetric determination of fluoride in some pharmaceutical products used for fluoridation

Two titrimetric methods were developed for the determination of fluoride contents in some pharmaceutical preparations used for fluoridation. One of the methods is catalytic controlled-current potentiometry involving two identical platinum indicator electrodes and thorium nitrate as titrant. The reaction between hydrogen peroxide and potassium iodide in the presence of acetate buffer (pH 3.6), which is catalysed by the excess of thorium nitrate, served for the end-point indication. The other method is the automatic potentiometric titration involving a fluoride-selective electrode and lanthanum nitrate as titrating agent. In both procedures, special attention was paid to sample pretreatment and to determination of optimal experimental conditions. Fluoride contents in the range 16-32 microg/ml are determined with a relative standard deviation less than 1.34%. The results are compared to those obtained by standard methods described in the United States Pharmacopeia XXI and recommended by the manufacturer of the preparations.     

Contributions to the basic problems of complexometry-XXIV Determination of aluminium in the presence of very large amounts of manganese

A simple complexometric determination of aluminium in the presence of a large amount of manganese has been developed. For such determinations only triethylenetetraminehexa-acetic acid (TTHA) can be used. In slightly acidic medium TTHA forms with aluminium a binuclear complex Al(2)L. The complex is formed almost immediately at room temperature. The excess of TTHA is backtitrated with copper sulphate at pH about 5.3, with Glycinecresol Red as indicator. Reliable results were obtained for Mn:Al ratios up to at least 20. The sum of Al + Fe can be determined by the same method. Very large amounts of calcium and magnesium do not interfere.     

Determination of Thorium and Total Rare Earths in Monazite Sand with Fluoride Electrode

A new method has been proposed to determine the total rare earths and thorium in monazite sand with fluoride electrode. The total amount of thorium and rare earths could be determined by back-titration with standard lanthanum solution in excess fluoride, and the rare earths were titrated directly with fluoride from separate sample. Fluoride electrode was used as indicator electrode. Precision and accuracy were improved by Gran's plot technique.     

Compleximetric titrations of iron(III) and iron(II) with triethylenetetraminehexaacetic acid

The stability constants of the iron(II) complexes of TTHA (triethylenetetraminehexaacetic acid) were calculated from measured pH and redox potentials. The values of the cumulative constants obtained were: log β_FeL= 15.37, log β_FeHL = 23.83, log β_FeH2L = 28.0, log β_Fe2L = 24.73. On the basis of these values and the previously determined constants ofiron(III) complexes, the possibilities of titrating iron(III) and iron(II) with TTHA were investigated. Depending on the experimental conditions, either FeL or Fe₂L formed. Actual titrations were in agreement with the developed theory. The influence of aluminium and titanium on titrations of iron(III) solutions was elucidated.     

Analytical application of embelin

Summary Embelin is reported as a new reagent for gravimetric estimation of (1) uranium in pure solutions at p_H 6.0–6.5 and (2) thorium in acid solutions of 0.4 N HCl. In both cases, the precipitates were ignited and weighed as U₃O₈ and ThO₂. The separation of thorium from large excess of uranium and rare earths could also be effected employing this reagent. In addition, Cu, Cd, Ca, Ba, Sr, Al, Be, Mn, Mg and Zn do not interfere.     

Isotopic compositions of terrestrial thorium: A search in terrestrial thorium for the unidentified excess 4.6 meV alpha-activity of lunar thorium

Since thorium in lunar crystalline rocks was reported to be excessive in 4.6 MeV alpha-activity up to 80%, which was attributed to a long-lived isomer of²³²Th with an origin different from normal thorium, we have measured alpha-spectra of various terrestrial thorium in order to see if terrestrial thorium also contains some excess 4.6 MeV alpha-activity. The results showed that the content of the excess 4.6 MeV alpha-activity in terrestrial thorium, if any, is much less than 3%. An approach to set an upper limit for the excess alpha-activity in terrestrial thorium is proposed. The origin of the excess alpha-activity is discussed.     

Synthesis, crystal structures, and properties of oxovanadium(IV)-lanthanide(III) heteronuclear complexes

A new series of oxovanadium(IV)-lanthanide(III) heteronuclear complexes [Yb(H2O)8]2[(VO)2(TTHA)](3)21 H2O (1), {[Ho(H2O)7(VO)2(TTHA)][(VO)2(TTHA)](0.5)} 8.5 H2O (2), {[Gd(H2O)7(VO)2(TTHA)][(VO)2(TTHA)](0.5)}8.5 H2O (3), {[Eu(H2O)7][(VO)2(TTHA)](1.5)} 10.5 H2O (4), and [Pr2(H2O)6(SO4)2][(VO)2(TTHA)] (5) (H6TTHA=triethylenetetraaminehexaacetic acid) were prepared by using the bulky flexible organic acid H(6)TTHA as structure-directing agent. X-ray crystallographic studies reveal that they contain the same [(VO)2(TTHA)]2- unit as building block, but the Ln3+ ion lies in different coordination environments. Although the lanthanide ions always exhibit similar chemical behavior, the structures of the complexes are not homologous. Compound 1 is composed of a [Yb(H2O)8]3+ ion and a [(VO)2(TTHA)]2- ion. Compounds 2 and 3 are isomorphous; both contain a trinuclear [Ln(H2O)7(VO)2(TTHA)]+ (Ln=Ho for 2 and Gd for 3) ion and a [(VO)2(TTHA)]2- ion. Compound 4 is an extended one-dimensional chain, in which each Eu3+ ion links two [(VO)2(TTHA)]2- ions. For 5, the structure is further assembled into a three-dimensional network with an interesting framework topology comprising V2Pr2 and V4Pr2 heterometallic lattices. Moreover, 4 and 5 are the first oxovanadium(IV)-lanthanide(III) coordination polymers and thus enlarge the realm of 3d-4f complexes. The IR, UV/Vis, and EPR spectra and the magnetic properties of the heterometallic complexes were studied. Notably, 2 shows unusual ferromagnetic interactions between the VO2+ and Ho3+ ions.     

A POTENTIOMETRIC STUDY OF METAL CHELATES WITH TETRAETHYLENEPENTAAMINEHEPTA-ACETIC ACID

Abstract

The protonation constants of tetraethylenepentaamineheptaacetic acid, TPHA, were determined by potentiometric titration in aqueous solution at an ionic strength of 0.10 M KNO₃ and at 25°C. The formation constants of various metal-TPHA complexes were also obtained by titrating mixtures of metal to ligand in molar ratios of 1 :1 and 2:1. Calculations were performed with the computer program BEST. Individual stability constants are reported for Co(II). Ni(II), Cu(II), Zn(II), Cd(II), Hg(II) and Pb(II) with TPHA as well as their related pro-tonated species. The stabilities of the 1:1 complexes parallel to those of similar complexes with DTPA and TTHA. However the 2: 1 complexes have significantly larger log K _ML's than their TTHA counterparts. The extra stability of the 2:1 metal-TPHA complexes is explained in terms of ligand denticity and steric effects. Mercury(II)-TPHA complexes exhibited the highest formation constants and the copper-TPHA complexes had slightly higher log K _ML's than those for Co(II), Ni(II), Zn(II), Cd(II) and Pb(II).     

水溶液中Ln(Ⅱ)-TTHA络合物的多核NMR研究

通过对11种镧系-三乙烯四胺六乙酸络合物诱导的²³Na、²H、¹⁷O和³⁵Cl的化学位移测定,研究了该系列络合物的位移试剂性质。结果表明,轴对称的Ln(TTHA)^3-络合物是较好的水溶性位移试剂,尤其是²³Na位移与理论偶极位移一致,表明此络合物是最好的正电荷底物之一。     

Studies in bivalent chromium salts

Summary As shown above, the estimations of potassium persulphate, hydrogen peroxide and dissolved oxygen in water, can be carried out with the help of chromous sulphate, by either of the two methods: (i) adding excess of chromous sulphate and titrating the excess with ferric solution using thiocyanate as indicator; (ii) adding to an excess of ferrous solution and titrating the ferric iron produced with chromous sulphate, using neutral red or thiocyanate as indicator. The results obtained by the above two methods are fairly satisfactory.Part III: cf. Z. analyt. Chem. 159, 5 (1958).The authors' thanks are due to the College authorities for providing the necessary facilities for work.     

The determination, in forensic toxicology, of metallic poisons by paper chromatography

Summary Precipitation of ThFe(CN)₆ from a solution of thorium nitrate with potassium ferrocyanide at varius concentrations has been carried out for the estimation of thorium. The precipitate was filtered and the excess of ferrocyanide was titrated with standard ceric sulphate solution. The amount of potassium ferrocyanide thus used was obtained and the amount of thorium calculated.Having established by the physico-chemical methods that the formula for thorium ferrocyanide is ThFe(CN)₆, under all conditions, it has now become possible to estimate thorium volumetrically by the ferrocyanide method.     

Determination of traces of rare earths in high-purity thorium dioxide by neutron activation analysis

The use of thorium dioxide as a nuclear fuel requires the determination of individual rare earth impurities at 0.08–1 mg kg^?1 levels. Neutron activation is sufficiently sensitive but separation from the matrix is essential. In the proposed method, thorium dioxide (5–20 g) is dissolved in concentrated nitric acid with a little hydrofluoric acid; after evaporation, thorium is complexed with ammonium carbonate and the solution is passed through a small column of Chelex-100 resin which retains the rare earths quantitatively without retaining thorium. The rare earth elements are eluted with dilute nitric acid, concentrated, and irradiated with standards; after irradiation the rare earth are collected on a lanthanum carrier and measured by γ-ray spectrometry. The recoveries of rare earths were checked with tracers and by standard addition to thorium dioxide matrices. The reproducibility for La, Eu and Dy was satisfactory at 0.01, 0.003 and 0.002 mg kg^?1, respectively; as was the reproducibility for all rare earths added to thorium dioxide (1–4 μg/5 g). Limits of detection are adequate for certification of nuclear-grade material.     

Anion-exchange behavior of rare earths,thorium, protactinium and uranium in thiocyanate-chloride media

The anion exchange of rare earths(III), thorium(IV), protactinium(V) and uranium (VI) from thiocyanate-chloride media was investigated. The equilibrium, distribution study showed that the rare earths(III) and yttrium(III) were not significantly adsorbed on a basic anion-exchangc resin, while thorium(IV), protactinium(V) and uranium(VI) were strongly adsorbed. Adsorption from the thiocyanate-chloride solutions is in the order, U(Vl) > Pa(V) > Th(IV). The separation of rare earths(III) or yttrium(III), thorium(IV), protactinium(V) and uranium(VI) was successfully accomplished by column elution in thiocyanate-chloride media. A rapid and effective ion-exchange method for separating protactinium-233 from irradiated thorium(IV) is also presented.