Contributions to the basic problems of complexometry—XIII Determination of aluminium and tervalent chromium in the presence of chromate

Aluminium can be determined in the presence of tervalent chromium and chromate using 1,2-diaminocyclohexanetetra-acetic acid (DCTA), which forms a complex with aluminium even in the cold. This phenomenon enables a successive determination to be made of aluminium (iron) and tervalent chromium in the presence of hexavalent chromium. This procedure cannot be carried out with the commonly used ethylenediaminetetra-acetic acid (EDTA).     

Contributions to the basic problems of complexometry—X: Determination of nickel and cobalt in the presence of iron, copper and some other metals

A complexometric determination of nickel and cobalt in the same solution has been devised. It is based on the determination of the sum of nickel and cobalt by back-titration of added excess EDTA in a strongly alkaline medium with calcium chloride using Fluorexon (Calcein) as indicator. After oxidation of cobalt with hydrogen peroxide to form the cobalt^III- EDTA complex and screening of nickel by potassium cyanide, the liberated EDTA corresponding to the amount of nickel present is titrated with further calcium chloride. High concentrations of iron and aluminium are screened with triethanolamine. Copper and other heavy metals are screened with thioglycollic acid.     

Contributions to the basic problems of complexometry—VIII Thioglycollic acid as a masking agent

The masking properties of thioglycollic acid (TGA) as well as the possibilities of its use in complexometry have been studied. It has been found that thioglycollic acid in an alkaline medium perfectly masks metals such as Pb, Bi, Cd, Ag, Hg, Zn, Tl, In and Sn because of the formation of colourless complexes. In this medium TGA forms intensely coloured complexes with Fe, Co and Ni. The red coloration of the Fe-TGA complex can be prevented by the addition of triethanolamine. It has been found that the Ni- and Co-EDTA complexes do not react with TGA. This enables a highly selective determination of nickel and cobalt to be made. Also, manganese can be determined in the presence of other metals screened with TGA. The advantages of TGA in comparison with potassium cyanide are discussed.     

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.     

Contribution to the basic problems of complexometry—III Some advantages of acetate buffer

Acetate buffer, in conjunction with additives such as o-phenanthroline or :'-bipyridyl, permits the titration of metallic cations such as copper with EDTA in weakly acid medium, using Xylenol Orange of Methyl Thymol Blue as indicators. In this it is superior as a buffer to the more generally used urotropine. The nature of its action is discussed.     

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.     

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.     

Contributions to the basic problems of complexometry-XX Determination of calcium and magnesium

A new method for the determination of magnesium in the presence of calcium is described. Calcium is masked with EGTA whilst magnesium is titrated with DCTA with Methylthymol Blue as the indicator. Calcium can be determined in the same solution by back-titration of the excess EGTA with calcium chloride solution. The usual masking agents for iron, aluminium and other heavy metals can be used.     

Determination of soluble lignin and proteins in the presence of each other

Several methods for the differential determination of lignin and of proteins solubilized together in the same solution are compared. It is shown that lignin is best determined by spectrophotometry at 280 nm, the absorptivity of the polymer being an order of magnitude greater than those of proteins. In contrast, a turbidimetric method applied to acid-precipitated lignin is strongly influenced by both the nature and the amounts of the proteins present in the mixture. Ninhydrin reagents permits the determination of proteins without interference from soluble lignin. Phenol and Coomassie Blue reagents react strongly with lignin, thus masking their interaction with proteins. The soluble lignin preparations used were solubilized from stake lignin in buffers adjusted to different pH values. They were analysed by exclusion chromatography and the results suggest that the lignin fragments obtained at higher pH are larger than those solubilized at lower pH. Turbidimetry showed that these larger soluble fragments form larger aggregates after acid precipitation.     

Contributions to the basic problems of complexometry-XXI: determination of nickel in the presence of cobalt

A new method for the determination of nickel in the presence of cobalt, based on the masking of the cobalt with potassium cyanide and hydrogen peroxide, is proposed. The yellow, or orange-yellow, complex of cobalt(III) is formed, from which cobalt is not displaced upon the addition of silver nitrate. Tetracyanonickelate, however, reacts quantitatively with silver nitrate, and the displaced nickel can be determined directly with EDTA, using Murexide as indicator. Up to 30 mg of cobalt can be tolerated in the solution.     

Contributions to the basic problems of complexometry-XXV Determination of rare earths and phosphate without separation

A new method for coraplexometric determination of rare earths (RE) and phosphate without prior separation is described. It is based on indirect determination of RE by back-titration of an excess of DTPA with zinc solution, with Xylenol Orange as indicator. After the titration an excess of La-EDTA complex solution is added and the solution is titrated again with zinc at 40-50 degrees . During this titration lanthanum is displaced from its complex and precipitated as phosphate: LaY(-) + Zn(2+)+ PO(4)(3-) = LaPO(4) + ZnY(2-). The consumption of zinc solution corresponds to the amount of phosphate.     

Contributions to the basic problems of complexometry-XXVI determination of calcium in the presence of large amounts of magnesium

Two methods for the determination of calcium in the presence of very large amounts of magnesium are proposed. Both are based on back-titration of excess of EGTA, Thymolphthalexone being used as indicator. In the one method the titrant is a zinc solution, in the other a calcium solution is used, with a small amount of zinc present for end-point indication. Both titrations can be performed either visually or spectrophotometrically.     

Determination of calcium,magnesium, and phosphate in the presence of iron and each other

Excess EDTA and MgSO₄ solution is added to a mildly acidic solution of the sample containing calcium, magnesium, iron, and phosphate ions. Addition of NH₄OH to this solution results in the precipitation of MgNH₄PO₄·6H₂O and various iron compounds. Calcium ions and a portion of the magnesium ions stay in the solution as the respective EDTA chelates. The mixture is adjusted to a known volume and filtered. The EDTA content of the filtrate with the exception of the EDTA tied up as calcium-EDTA chelate, is titrated with standard CaCl₂ solution at pH 12.5–13.0 in the presence of hydroxy naphthol blue indicator. The calcium content of the sample can be calculated from the result of this titration.     

Determination of maleic acid and fumaric acid in the presence of each other by thermal analysis

The thermal properties of fumaric acid and maleic acid were investigated. It was found that differences in their thermal decompositions provide a possibility for their determination. The thermoanalytical determination of their mixtures was carried out derivatographically.     

N-acetylsalicyloyl-N-phenylhydroxylamine as an analytical reagent Determination of niobium and tantalum in the presence of each other

N-Acetylsalicyloyl-N-phenylhydroxylamme is proposed for the separation of niobium(V) and tantalum(V) and their gravimetric determination. Niobium is precipitated at pH 5.5-6.5 by the reagent and the complex is weighed directly. Tantalum is precipitated from 1-2M hydrochloric acid solutions and the complex is ignited to tantalum pentoxide. The method is fairly selective. In the presence of thiocyanate the reagent forms an extractable complex with niobium. The reaction forms the basis of a selective and sensitive spectrophotometric determination of niobium.     

Estimation of di- and tri-chloracetaldehydes in the presence of each other

Summary Both di- and tri-chloracetaldehydes can be estimated by (i) hydrolysis with standard KOH, (ii) titrating argentometrically the Cl^– formed during hydrolysis and (iii) oxidation with alkaline iodine. Only trichloracetaldehyde gives the Fujiwara colour reaction and can be determined colorimetrically. Based upon the combination of alkalimetry and iodometry and that of colorimetry with iodometry or argentometry, three methods for the estimation of di- and tri-chloracetaldehydes in the presence of each other are described. Limits of the applicability of these procedures under various conditions are defined.Sincere thanks of the authors are due to Professor S. S. Joshi, Head of the Chemistry Department, Banaras Hindu University, for facilities and keen interest in the work.     

Polarographic determination of uranium and lead in the presence of each other

Summary The microanalysis of solutions of dioxouranium- (VI) has been investigated employing differential pulse polarography. These studies show that uranium and lead can be determined accurately and economically in the presence of each other. The lead current peak occurs at –0.325 V, the uranium peak at – 0.200 V. Quantitative determinations are possible in the presence of Bi, Zn, Co and Fe.

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Polarographische Bestimmung von Uran und Blei nebeneinander

     

Determination of phthalic,terephthalic, and isophthalic acids in the presence of each other by gas chromatography

A procedure was developed for the simultaneous determination of phthalic acid isomers; the procedure includes the preparation of diisoamyl esters by reaction with isoamyl alcohol in a benzene solution in the presence of sulfuric acid with the distillation of an azeotrope mixture of benzene with water, the neutralization of acid with triethylamine, and the separation of esters by gas-liquid chromatography on a steel column (1 m × 3 mm) filled with Chromaton N-AW-HMDS with 5% Apiezon L in the temperature programming mode with flame-ionization detection. The time of separation is 13 min. The time of the sample preparation step is 2–2.5 h. The lower determination limit is 20 ng. The procedure allows the determination of phthalic acids in the concentration range from 0.02 to 2 mg/L in liquid samples and from 0.03 to 3 mg/m³ in air.