Polarography of intermediates in the fixation of nitrogen by p-quinone-aqueous ammonia systems

Air oxidation of aqueous p-quinone, as a model humic acid precursor, develops precipitates of different character in the presence and absence of ammonia. Polarographic analyses of the p-quinone-ammonia systems at different ammonia concentrations, pH levels, and reaction times reveal two reducible intermediates in the reaction leading to fixation of nitrogen. The intermediates give half-wave potentials, at pH 8.3, of — 0.25 and — 0.55 V vs. S.C.E. The waves are interpreted as resulting from the reduction of mono- and disubstituted aminoquinones. A mechanism and structure are proposed for the nitrogen-containing polymerization product.     

Use of nitrosochromotropic acid as a metal indicator

Summary Nitrosochromotropic acid and copper give a purple coloured complex in the pH range 5.8–6.5, which is less stable than Cu(II)-EDTA complex. When milligramme quantities of copper solution containing few drops of nitrosochromotropic acid were titrated with EDTA the colour changes to light green or colourless. Copper can be titrated from 15–30° C, but at higher temperature low results are obtained due to dissociation of copper complex. Alkaline earths do not interfere in the titration of copper, but zinc, cadmium, nickel, cobalt, aluminium and iron(III) interfere. The interference of aluminium and iron(III) is masked by sodium fluoride. Microtitration can be carried out using nitrosochromotropic acid screened with xylene cyanol FF as metal indicator.     

Coulometric generation of molybdenum(v)

Molybdenum (V) was generated at a platinum cathode from 0.7 M molybdenum(VI) in 4 M sulfuric acid. A current efficiency of 99.9% was attained. A limiting current density of 0.05 mA/cm²/mM was found. The formal potential of the Mo(VI)–Mo(V) couple in 4 M sulfuric acid was determined to be ca. 0.55 V vs. N.H.E. Chromium(VI) solutions were titrated over a wide range of sample size and generating current. Amperometric titration curves were interpreted from current-voltage curves. Titrations could be performed in the presence of oxygen at the 1μeq. level. The effect of nitrate, perchlorate, orthophosphate, and chloride ions on the titration was determined.     

EDTA滴定法测定再生锌原料中的锌含量

采用氟化铵-盐酸-硝酸-硫酸分解样品,氨水沉淀分离铁、锰、铅等共存元素,滤液中加入掩蔽剂掩蔽少量干扰元素,在pH=5～6的乙酸-乙酸钠缓冲溶液中,以二甲酚橙为指示剂,用EDTA标准滴定溶液滴定。测得结果为锌、镉合量,扣除镉量,即为锌量。方法用于测定再生锌原料中锌,结果的相对标准偏差(RSD,n=11)为0.15%～1.0%。按照实验方法对再生锌原料样品进行加标回收实验,回收率为99.1%～102%。能满足日常对再生锌原料中锌含量的检测要求。     

Studies in polarographic analysis : Determination of manganese after oxidation to the manganic state stabilized by triethanolamine

The manganic complex with triethanolamine, prepared by the oxidation of manganous solution in presence of 0.5M NaOH and 4% by volume triethanolamine with atmospheric oxygen, is found suitable for the polarographic determination of manganese. Under these conditions, the diffusion current is proportional to the Mn⁺² concentration from 2.10^-4·7.10^-3ME$\text{1}\text{2}$,for the Mn⁺³/Mn⁺² wave = — 0.5 V vs S.C.E. The temperature coefficient for the diffusion current 1.2% per degree I and D° decrease by increasing the alkali or triethanolamino concentration. They amount in presence of NaOH = 0.5M and 4% triethanolamine to I = 1.27 and D° = 4.18·10^-6 cm²/sec.     

Photometric titration of iron with ethylenediaminedi(o-hydroxyphenylacetic acid)

Fractional mg quantities of ferric iron in 100 ml of solution can be titrated at PH 3.5 with a solution of ethylenediaminedi(o-hydroxyphenylacetic acid). The end-point is found photo- metrically. Errors are generally under 1%, and a number of metals do not interfere. By scaling down the volume of the solution and the titrant concentration, the titration can be extended to μg quantities of iron, and mg quantities are also accessible by changing to a wave length where the sensitivity is not so great. The titration may be useful in certain applications.     

Microdetermination of aliphatic diamines and polyamines with cupric ion

The reactions of diamines and polyamines with cupric ion were investigated potentiometrically, using a copper ion-selective indicator electrode and a single-junction reference electrode. In general, cupric ion reacted with 2 mol of vic-diamines or their salts. Tetraaza compounds reacted on an equimolar basis with Cu(II). Both vic-diamines and their salts, as well as tetraaza compounds, could be titrated in the presence of excess ammonia. With cupric ion in ammoniacal solution these compounds yield a characteristic purple/violet color. Diamines separated by more than two methylene groups cannot be determined in the presence of ammonia and yield a blue color. Diamines with more than four methylene groups react with cupric ion on an equimolar basis, also yielding a blue color.     

The influence of hydrogen peroxide and pH on the Mohr titration

The official Japanese method for determination of chloride in hot-spring waters requires any H(2)S present to be oxidized with hydrogen peroxide in ammoniacal medium. When this was done, and the solution was titrated with silver nitrate at pH 9.7, the indicator colour changed from yellow to brownish grey, owing to reduction of silver ions to the metal by hydrogen peroxide. The effect can be eliminated by adjusting the pH to 7.0-7.5 before the titration.     

Complexometric titration of copper (II) using chromotropic acid dioxime as a metal indicator

Summary Chromotropic acid dioxime forms purple coloured complexes with copper in the p_H ranges 5.82 to 6.45 and 7.25 to 8.05 respectively which are less stable than the Cu^II-EDTA complex. On titrating these solutions with EDTA, the purple coloured complexes turn colourless or yellow at the end point. These titrations give satisfactory results in the temperature ranges 20 to 70° C and 20 to 50° C respectively. In acid medium, the titration of copper can be carried out in the presence of magnesium and alkaline earths, but zinc, cadmium, nickel, cobalt, aluminium and iron(III) interfere. The latter two elements can be masked by sodium fluoride. In ammoniacal medium, zinc, cadmium, cobalt, nickel, lead, magnesium and alkaline earths interfere.

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Zusammenfassung Chromotropsäuredioxim bildet mit Kupfer im p_H-Bereich 5,82 bis 6,45 und 7,25–8,05 purpurrot gefärbte Komplexe, die weniger stabil sind als der Kupfer-ÄDTA-Komplex. Bei der Titration solcher Lösungen mit ÄDTA ergibt sich am Endpunkt ein Farbumschlag nach Farblos bzw. Gelb. Bei Temperaturen von 20–70°C bzw. 20–50°C werden gute Ergebnisse erzielt. Die Kupferbestimmung in saurem Medium kann in Gegenwart von Magnesium und Erdalkalien durchgeführt werden; Störungen werden verursacht durch Zink, Cadmium, Nickel, Kobalt, Aluminium und Eisen(III), wobei die beiden letzten jedoch mit Natriumfluorid maskiert werden können. Die Titration in ammoniakalischem Medium wird durch Zink, Cadmium, Kobalt, Nickel, Blei, Magnesium und die Erdalkalien gestört.

     

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.     

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.     

Coulometric determination of chromium

This paper describes an accurate and precise method for the determination of chromium by coulometry at controlled potential. A solution of the sample in 6M hydrochloric acid is electrolyzed at a large stirred mercury cathode whose potential is maintained constant at —1.10 V vs. S.C.E. ;this reduces the chromium quantitatively to the +2 state. Copper, lead, and a number of other elements are next eliminated by simply discarding the mercury and replacing it with fresh mercury ;then uranium is re-oxidized to non-interfering uranium(IV) by a second controlled-potential electrolysis at —0.80 V vs. S.C.E.; and finally the solution is electrolyzed at a working electrode potential of —0.40 V vs. S.C.E. This serves to re-oxidize the chromium quantitatively to the +3 state, and the analysis consists of measuring the quantity of electricity consumed in this oxidation.Of the elements commonly associated with chromium, only vanadium (and, when it is present in large amounts, molybdenum) interfere in this procedure.     

Mercurous nitrate as a reductimetric reagent: The potentiometric titration of ferric iron in the presence of ions forming highly coloured thiocyanates

The reduction of ferric iron by means of mercurous salts in the presence of an excebs of ammonium, thiocyanate can be predicted on theoretical grounds. By consideration of the oxidation potentials involved it has been shown by calculation that quantitative reduction of the ferric iron is to be expected.—The titration may be effected potentiometrically using a bright platinum indicator electrode in conjunction with a silver/silver chloride electrode or a saturated calomel reference electrode. Ferric iron can be titrated in the presence of ions such as cobalt which form intensely coloured thiocyanate complexes.A possible method for the titration of molybdate by means of mercurous nitrate has been examined. The sensitivity of the method suffers from the instability of potential of the system under titration, but particularly since tungstate does not interfere, the method is worthy of further study.     

Determination of thallium and lead in cadmium salts by anodic stripping voltammetry with addition of surfactants to suppress the cadmium peaks

Conditions have been found which make possible the determination of thallium and/or lead in cadmium and its salts without preliminary separation. The electrochemical activity of the cadmium, which usually interferes in the determination of thallium, is inhibited by the addition of 0.01% of polyethylene glycol of M.W. 4000. Thallium is determined by electrolysis at ?0.74 V vs. SCE, in 0.1M EDTA solution: 10^?1M thallium can be determined in the presence of 0.1M cadmium, while copper and lead at 10^?2M and 10^?5M respectively do not interfere. Lead is determined in 0.1M acetic acid containing 0.1% cetyltrimethylammonium bromide (CTAB). The addition of CTAB shifts the cadmium peak, as well as the optimum deposition potential for cadmium, to more negative values, making it possible to determine lead in the presence of cadmium as long as the deposition potential lies in the range between ?0.50 and ?0.56 V vs. SCE. Lead can be determined in the presence of ten times as much thallium.     

Chronopotentiometric and controlled-potential electrolytic studies of the formation of intermetallic compounds in copper-zinc,platinum-zinc,and other amalgams

The behaviors of amalgams containing: copper and zinc; platinum and zinc; platinum and cadmium; silver and zinc; silver and cadmium; cadmium and copper; cadmium, copper and platinum; and silver, nickel and zinc were investigated by controlled-potential electrolysis and chronopotentiometry. Copper-zinc amalgams contain the compound CuZn, for which the solubility product at 25°C is equal to (3.8±0.6)×10^?6M², and also a soluble but sparingly dissociated compound that is richer in zinc. Platinum-zinc amalgams contain PtZn₂, PtZn₃ and PtZn₄ in metastable equilibrium. Gold-cadmium amalgams contain the compound AuCd, whose solubility product at 25°C is equal to (1.7±0.1)×10^?5M². Compound formation could not be detected in silver-zinc, silver-cadmium, cadmium-copper, platinum-copper or cadmium-copper-platinum amalgams, but there was an uncertain indication that silver-nickel-zinc amalgams might contain the first ternary intermetallic compound found in amalgams.     

Electrochemical approach to detect the presence of peroxynitrite in aerobic neutral solution

This work describes the conditions of use of bare gold electrode to detect electrochemically the presence of peroxynitrite ONOO^? in phosphate buffer solution at pH 7.1. As ONOO^? is extremely unstable in neutral solution, current–potential curve was reconstructed between ?0.5 and 0.7 V vs SCE by amperometry experiments at rotating disk electrode at different potentials. Comparison of this reconstructed curve with voltammograms of the common interfering species (dopamine, hydrogen peroxide, nitrite, ascorbic acid and glutamate) shows that the presence of ONOO^? can be selectively determined at ?0.1 V vs SCE. This detection occurs through the electrochemical reduction of peroxynitrous acid ONOOH, the conjugated acid of ONOO^?. Detection of ONOO^? produced in situ by the reaction of nitric oxide with superoxide was also achieved.     

Sodium meta-vanadate as volumetric reagent: Iodine monochloride method

In hydrochloric acid medium sodium meta-vanadate was used as a volumetric reagent for the determination of copper, zinc, cobalt, mercury, and lead. Cu⁺², Zn⁺² and Co⁺²were precipitated as complex mercurythiocyanates, Hg⁺² as mercuric zinc thiocyanate and Pb⁺² as Iodide. The thiocyanates were dissolved in concentrated hydrochloric acid and titrated against standard sodium meta-vanadate solution in the presence of iodine monochloride as a pie.oxidizer and catalyst. In titration of the iodide against the meta-vanadate. it was not necessary to add iodine monochloride to the titrant because it is formed during the titration. Chloroform was used as an indicator. It was pink owing to the liberation of iodine during the titration and became pale yellow at the end-point because of the formation of iodine monochlonde.     

Photochemical Titration of Imine Chelons

Abstract

A photochemical titration for determination of the analytically useful imine chelons 1,10-phenanthroline and 2,4,6-tripyridyl-s-triazine has been developed. The titrant, iron(II), is photolytically generated from iron(III)-citrate; citrate buffers the solution permitting rapid reaction of iron(II) with the chelons. A single mercury vapor arc serves as source for both photolysis and the photometric end point (546 nm); 1 to 40 micromoles of chelon can be titrated with RSDs less than 1%. 2–2′ bipyridine cannot be titrated by continuous photolysis due to a slow complex formation step.     

沉淀分离-EDTA滴定法测定铜闪速冶炼烟尘中的锌量

称取0.5 g试样,用盐酸、硝酸、硫酸分解,铅以硫酸铅沉淀的形式分离.以过硫酸铵为氧化剂,氨性溶液中沉淀分离铁、锰等共存元素,加氟化物掩蔽铝、硫脲掩蔽铜,调节溶液pH=5.0～6.0,加入碘化钾消除镉的干扰,以二甲酚橙为指示剂,用ED TA标准溶液滴定.将沉淀物重新溶解,用原子吸收光谱法测定其中的锌量.在0.2％ ～1...     

Diphosphine derivatives: Part 5. Ligand behaviour and vibrational spectra of coordinated tetraalkyl-1,2-dithioxodi-λ5-phosphanes (tetraalkyldiphosphine disulphides)

Vibrational data are reported for complexes of tetraethyl-,tetrapropyl-and tetrabutyl-1,2-dithioxodi-λ⁵-phosphanes (tetraalkyldiphosphine disulphides) P₂R₄S₂ with zinc, cadmium, mercury and cobalt halides. The P—P stretching frequencies in the coordinated ligands occur near 500 cm^?1, substantially higher than in the corresponding P₂Me₄S₂ complexes, most probably because of interactions with P—C—C deformation modes. In the F—C stretching region the spectra of the P₂Et₄S₂ complexes are consistent with (but do not necessarily prove) cis-chelate ligand geometry with Zn, Cd and Co halides, and gauche-chelate geometry with Hg halides. No M—S stretching vibrations can be identified above 250cm^?1.