Process monitored spectrophotometric titration coupled with chemometrics for simultaneous determination of mixtures of weak acids

A new spectrophotometric titration method coupled with chemometrics for the simultaneous determination of mixtures of weak acids has been developed. In this method, the titrant is a mixture of sodium hydroxide and an acid-base indicator, and the indicator is used to monitor the titration process. In a process of titration, both the added volume of titrant and the solution acidity at each titration point can be obtained simultaneously from an absorption spectrum by least square algorithm, and then the concentration of each component in the mixture can be obtained from the titration curves by principal component regression. The method only needs the information of absorbance spectra to obtain the analytical results, and is free of volumetric measurements. The analyses are independent of titration end point and do not need the accurate values of dissociation constants of the indicator and the acids. The method has been applied to the simultaneous determination of the mixtures of benzoic acid and salicylic acid, and the mixtures of phenol, o-chlorophenol and p-chlorophenol with satisfactory results.     

Sodium metavanadate as volumetric reagent : Determination of organic derivatives of hydrazine,iodine monochloride method

Sodium metavanadate has been used as an oxidising agent in hydrochloric acid medium for the volumetric determination of semicarbazide hydrochloride, benzalazine, benzalsemicarbazone, aminoguanidine hydrochloride, o-hydroxybenzalsemicarbazone, p-methoxybenzalsemicarbazone, chloralhydrazine, o-chlorobenzalsemicarbazone and ethyl methyl ketone semicarbazone, using 10-dine monochloride as a catalyst and preoxidiser Chloroform was used as an indicator. It was coloured violet due to the liberation of iodine during the titration and became light pale yellow at the end-point owing to the formation of iodine monochloride Eachhydrazino group in these compounds was oxidised quantitatively with a four-electron change to nitrogen with sodium metavanadate as an oxidant in hydrochloric acid solution.     

Analytical applications of thio. seleno and telluroethers: Part V. Titrimetric determination of palladium with sodium ethylene-bis-(thioglycolate)

Palladium solutions can be titrated visually and spectrophotometrically with sodium ethylene-bis (thioglycolate). Titrations were done in 2.5 M perchloric acid with nitroso-R salt as indicator. Palladium was determined in the range 5.0–30 mg (visual titration) and 2.0–10 mg (spectrophotometric titration): the tolerance for diverse ions is good, particularly with the spectrophotometric end-point. The probable structure of the isolated complex is given.     

Vanadametry Estimation of Thiosulphate

1.(a) We have found that sodium thiosulphate is quantitatively oxidized to tetrathionate in five minutes at room temperature (28°) by excess sodium vanadate in a medium containing sulphuric acid at 0.06N to 0.1N concentration and a little copper sulphate as catalyst. (b) Quantitative emulation of sodium thiosulphate to tetrathionate has also been achieved by the action of excess sodium vanadate during five minutes at room temperature in a medium containing 2.0N—8.0N acetic acid and a little copper salt as catalyst. Further oxidation to sulphate does not occur, even if the mixture is heated to boiling. (c) The excess of unreacted vanadate in 1(a) and 1(b) can be titrated with a standard solution of ferrous ammonium sulphate using diphenylbenzidine as indicator, after adding the requisite quantity of syrupy phosphoric acid. 2. On the other hand, sodium thiosulphate is easily and quantitatively oxidized to sulphate at room temperature, when. acted upon by excess sodium vanadate in a medium containing hydrochloric acid at an overall concentration of 5-6N and 1.0 ml of iodine monochloride as catalyst. The time required for reaction is ten minutes. The unreacted vanadate can be estimated by titration with a standard solution of ferrous ammonium sulphate, using N-phenylanthranilic acid as indicator or with diphenylbenzidine as indicator after suitably diluting and adding phosphoric acid.     

Semimicrodetermination of carboxylic acids in the presence of large amounts of acyl chlorides

A procedure for the semimicrodetermination of carboxylic acids in the presence of a large excess of acyl chloride is described. Acyl chloride is first reacted with m-chloroaniline. The m-chloroaniline hydrochloride and carboxylic acid are then determined sequentially by potentiometric titration with sodium hydroxide. Titrations are performed in 80–90% p-dioxane to enhance the potentiometric breaks. With 0.05 N sodium hydroxide, as little as 0.01 mM of carboxylic acid can be determined.     

Selective hydroxyl group determination by direct titration with lithium aluminum amide

The selective determination of hydroxyl groups in most complex alcohol systems by direct titration with standard lithium aluminum amide solution is described. The titration is carried out in ether solvent under nitrogen with N-phenyl-p-aminoazobenzene as reversible indicator. The accuracy is better than ± 1 % ; less than 6 min are required for a complete determination of alcohols up to triacontanol. Aldehydes, ketones, esters, amines and alkoxy groups do not interfere, but organic and inorganic acids, and water and molecular oxygen, interfere. Water and acid interferences can be corrected for after a Karl Fischer titration and neutralization reactions respectively.     

2-Nitrodiphenylamine as a versatile high-potential reversible oxidation-reduction indicator

The use of 2-nitrodiphenylamine as a reversible indicator has been investigated in the titration of iron(II) with cerium(IV) sulphate, potassium dichromate and sodium vanadate in sulphuric acid media. Accurate results can be obtained with cerium(IV) sulphate in 0.5–5.0 M acid, with potassium dichromate in 5.0–7.0 M acid, and with sodium vanadate in 5.0–7.5 M acid. With cerium(IV) sulphate the titrations are preferably conducted in 2.0 M sulphuric acid or in a 1.0 M. sulphuric acid-1.0 M pechloric acid medium. Tungstic acid, acetic acid, arsenic(III) and manganese(II) do not interfere. In titrations of iron(II) with dichromate and vanadate, the colour changes at the end-point are much more vivid with 2-nitrodiphenylamine than with ferroin.     

H/P NMR pH indicator series to eliminate the glass electrode in NMR spectroscopic pKa determinations

NMR titration is an efficient method to determine pK_a values of multiprotic acids in aqueous solution. While modern 1D/2D NMR techniques yield chemical shifts with increasing precision, the glass electrode-based pH measurement becomes the limiting factor to affect the precision of the resulting dissociation constants. The pH in the NMR tube can also be deduced from the actual chemical shift of an appropriate monoprotic indicator molecule. In the present work, the in situ NMR pH measurement has been extended for the entire pH range 0-12 using indicators with overlapping ranges of dissociation. In the first, calibrating ¹H/³¹P NMR titration, limiting chemical shifts and pK were determined for each indicator. An analysis of error propagation showed that the accuracy and precision of glass electrodes can be achieved at 1.8 < pH < 12 and even exceeded at pH extremes by NMR indicators, respectively. The assembled set of indicators was applied for in situ pH monitoring in the following “electrodeless” ¹H/³¹P NMR titration of a newly synthesized aminophosphinophosphonic acid. Multivariate nonlinear parameter estimation was used to calculate the pK values that were confirmed by potentiometric titrations.     

Chelating properties of n,n,n,n-tetrakis-(phosphonomethyl)-1,2-cyclohexanediamine

The octasodium salt of N,N,N',N'-tetrakis-(phosphonomethyl)-1,2-cyclohoxanediamine, Na₈-CDTMP, can be prepared in 45% yield from chloromethylphosphonic acid and 1,2-cyclohexanediamine. The titration curve resulting from the titration of the acid, CDTMP, with sodium hydroxide at 25° and μ = 0.1 was used to estimate the eight pK values for the free acid. The stability constants of metal chelatles of CDTMP were measured at 25° and μ = 0.1 potentiometrically.     

A contribution to the use of tetravalent manganese in solutions of sulfuric acid as an oxidimetric reagent

The preparation of solutions of manganese(IV) sulfate in 9 M sulfuric acid as well as the stability of these solutions was studied for 0.00501 M concentration of manganese(IV) ions. Potentiometric titration of solutions of primary standard substances, potassium iodide and sodium hexacyanoferrate, was recommended for determining the titer of 0.005 M reagent solutions. It was verified that manganese(IV) sulfate can be used for determining low concentrations of organic substances by direct titration determination of hydroquinone, p-aminophenol, and metol and by indirect determination of oxalic acid.     

The analysis of zirconium-thorium binary alloys

Thorium-zirconium binary alloys are analysed by complexometric procedures. For alloys containing more than 20% thorium or 5% zirconium by weight, the sum of the constituents is obtained by a back titration procedure at pH 2.6–2.8 with bismuth nitrate using xylenol orange as indicator. Thorium is then masked with sulphate and the liberated EDTA is titrated with bismuth at pH 1.2–1.3. For alloys containing less than 20% of thorium, thorium fluoride is precipitated on lanthanum fluoride to effect its separation before titration. For alloys containing less than 5% of zirconium, the zirconium is separated by precipitation with p-bromo-mandelic acid.     

Volumetric studies in oxidation-reduction reactions : Oxidation with sodium hypochlorite iodine monochloride method

Alkaline sodium hypochlorite was used as an oxidant to determine arsenious oxide, hydrazine sulphate, ferrous ammonium sulphate, stannous chloride, sodium sulphite, potassium iodide, mercurous chloride, thallous chloride and tartar emetic, by a volumetric method, using iodine monochloride as catalyst and preoxidizer. During these titrations, the normality of the solution with respect to hydrochloric acid was kept between 5N and 7N, Chloroform was used as an indicator. Its pink colour due to the liberation of iodine during the titration turns very pale yellow at the end-point because of the formation of iodine monochloride     

Synthesis and spectrophotometric studies of water-soluble amino[bis(ethanesulfonate)] azobenzene pH indicators

Three azobenzene pH indicators with amino[bis(ethanesulfonate)] substituents were synthesized and studied by UV–visible absorption spectroscopy in aqueous solution. The indicators exhibit brilliant and distinct colour changes with transitions between pH 1 and 4. Significant changes were observed in the UV–visible spectra on titration with acid with pK_a values ranging from 2.2 to 2.8. The indicators demonstrate individual changes in colour as a function of pH. These novel pH indicators complement the existing library of azobenzene indicator dyes and may be useful for environmental situations with high proton concentrations.     

Studies on adsorption indicators : p-ethoxychrysoidine as adsorption indicator

p-Ethoxychrysoidine is studied as adsorption indicator in the direct titration of silver with iodide, bromide, thiocyanate and chloride at pH 4–5. The explanation given by Schulek and Pungor for the colour changes has been modified in the light of compound formation on the surface of the precipitate. The silver compound of p-ethoxychrysoidine has been isolated ; its behaviour provides a suitable explanation for the colour changes as well as the pH changes in the titrations.     

Automatic potentiometric two-phase titration in pharmaceutical analysis : Part 3. Titrimetric Identification of Drugs

The conditional acidity constant in a liquid-liquid two-phase system (pK^*_HA + value) can be used as an identity parameter for drug compounds. The pK^*_HA + value can be calculated if the phase ratio and the acidity and distribution constants are known. Selectivity is obtained mainly by the choice of the organic phase. An excess of hydrochloric acid is first added to the sample in the two-phase system. The hydrochloric acid and the sample are then titrated sequentially with sodium hydroxide. The proposed titration procedure makes it possible to calibrat the electrodes, determine the pK^*_HA + value(s), quantify one or more compounds, and check the performance of the electrodes in one and the same experimental run. Lidocaine was “identified” and assayed in different dosage forms such as ointment and solution for injection. The results were in agreement with those obtained by liquid chromatography.     

Titration of antimony(III) with cerium(IV) sulphate and diphenylamine and its derivatives as reversible indicators

Diphenylamine, barium diphenylamine sulphonate, N-phenylanthranilic acid and 2-nitrodiphenylamine have been investigated as reversible indicators for the titration of antimony(III) with cerium(IV) sulphate in 0.5–2 M sulphuric acid medium. Diphenylamine is the most satisfactory in titrations of antimony(III) in chloride-free solutions, e.g. of potassium antimonyl tartrate. Even low chloride concentrations affect the indicator action of N-phenyl-anthranilic acid or 2-nitrodiphenylamine, but diphenylamine is satisfactory in 1 M hydrochloric acid media. Iodine catalyst is necessary to accelerate the reduction of the oxidized indicator by antimony(III). The indicator colour change is vivid and the colour of the oxidized indicator is stable. Titrations of antimony(III) in mixtures with iron(II) and arsenic(III) are also considered.     

Complexometric determination of thorium using p-nitrobenzene-azo-chromotropic acid (chromotrope 2-B) as indicator

Summary p-Nitrobenzene-azochromotropic acid (chromotrope 2 B) has been found useful as metal indicator in the titration of thorium ions against ethylenediaminetetraacetic acid. Titrations are best carried out with concentrations of thorium upto 0.001 M, within the p_H range 1.5 and 2.9. Temperature has no effect on the end point. Many of the common ions interfere in the titration excepting lithium, sodium, potassium, gold, alkaline earths, zinc, mercury, aluminium, lead, nickel, and acetate. Iron(III) if present may be masked by the addition of ascorbic acid.

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Zusammenfassung p-Nitrobenzol-azochromotropsäure (Chromotrope 2 B) wird als Metallindicator bei der komplexometrischen Titration von Thorium verwendet. Die besten Ergebnisse erhält man bei Konzentrationen bis 0,001 m im p_H-Bereich von 1,5–2,9. Die Temperatur hat keinen Einfluß auf die Erkennung des Endpunkts. Lithium, Natrium, Kalium, Gold, Erdalkalien, Zink, Quecksilber, Aluminium, Blei, Nickel und Acetat stören nicht, während viele andere Ionen Störungen verursachen. Eisen(III) kann mit Ascorbinsäure maskiert werden.

     

Single-point titrations: Part-I. The determination of bases

Equations are derived for the calculation of acid mixtures, which upon titration with base show a linear relation between pH and the amount of base. Three to five weak acids were used and a linearity of better than ±0.02 pH units was obtained. The use of such mixtures for analysis of the base content of samples by means of a single pH measurement is described. A procedure for obtaining conditional pK_a values of the components of the acid mixture is also described. The single-point titration method is advocated for use when better accuracy than that of direct potentiometry is desired but less than that of an ordinary titration can be accepted. It is not necessary to know the pK_b or the number of weak bases.     

The determination of microgram quantities of organic nitrogen

A method is descriibed for the determination of microgram quantities of nitrogen in a wide variety of materials. This method involves the Kjeldahl procedure for the conversion of nitrogen to ammonium or amine sulphate. Digestion of the sample with concentrated sulphuric acid and catalyst, and, if necessary, pretreatment with hydriodic acid and red phosphorus, are followed by steam-distillation into a dilute acid solution. The final determination depends on the reaction of ammonia, in a suitably buffered solution, with sodium hypobromite reagent, and measurement of the excess reagent by titration of the iodine liberated by it from acidified potassium iodide, with a standard $\text{N}\text{500}$ sodium thiosulphate solution, using sodium starch glycollate indicator.Since sample size is relatively unrestricted and the final titration can measure 5 micrograms of nitrogen, the sensitivity of the method is very high.Reference is made to existing sub-micro methodes which, although sensitive, are time-consuming and specific in application.