Semiautomatic indirect titration of alkaline-earth ions with catalytic endpoint indication

A semiautomatic spectrophotometric method of endpoint indication for indirect catalytic titrations of microamounts of alkaline-earth ions is described. The manganese(II)-catalyzed autoxidation of 1,4-dihydroxyphthalimide dithiosemicarbazone is used as indicator reaction. Calcium and magnesium (10–150 μg), strontium (20–250 μg), and barium (20–450 μg) can be determined by adding a known excess of EDTA to the sample solution and back-titrating the unconsumed inhibitor agent with standard manganese(II) solution. This catalytic method was applied to determine the total concentration in calcium and magnesium (total hardness) in natural waters and milk. The method is fast, accurate (1–3%), precise (0.2–0.8%, relative standard deviation), and specially useful for the determination of microamounts where metallochromic indicator are ineffective (for concentrations ranges below 10^?4M).     

Rapid chelatometric determination of bismuth, titanium and aluminium using Semi-Xylenol Orange with visual end-point indication

A rapid and simple general complexometric method was presented for the determination of bismuth, titanium and aluminium in laboratory synthesized alloys similar to those of some bauxites, clay, ilmenite, Portland cements and ceramic products. The precision and accuracy attainable in successive titrations of Bi(3+), Ti(4+) and Al(3+) with 0.01 and/or 0.001M solutions of disodium ethylenediaminetetraacetate (Na(2)EDTA) and standard ZnCl(2) of the same concentration, using Semi-Xylenol Orange (SXO) as a metallochromic indicator with visual end-point indication were studied. For one aliquot Bi(3+) was at first directly titrated at pH 1-2 (HNO(3)) with Na(2)EDTA using SXO as indicator in the presence of L-ascorbic acid to reduce Fe(3+) to Fe(2+). At the bismuth end-point, an excess of Na(2)EDTA was added, the pH was adjusted with hexamine buffer (pH 5) and the excess of Na(2)EDTA was back-titrated with solution of standard zinc(II) chloride for both the simultaneous and consecutive titrations in the presence of (SXO) as indicator. For the simultaneous titration, fluoride was added to release the Na(2)EDTA combined with both Al(3+) and Ti(4+). For the consecutive titration, phosphate was added to release the Na(2)EDTA combined with Ti(4+) and then fluoride to release the Na(2)EDTA combined with Al(3+). The interference of various anions and cations in the determination of Bi(3+), Ti(4+) and Al(3+) was studied. A comparison of the accuracy of both the simultaneous and consecutive titration was also carried out. The proposed methods were applied successfully to some real samples of bauxites, clay, ilmenite, Portland cements and ceramic products and the results were satisfactory.     

Complexometric determination of citric acid with copper

A method is presented in which citrate is determined by complexation with excess of copper(II), followed by back-titration with EDTA. Small amounts of citrate can be determined by this method in the presence of large amounts of most organic acids present in natural products. Interfering reductants are removed by treatment with permanganate, amino-acids with nitrous acid, and metal ions with a cation-exchange resin. The indicator used for end-point detection is Szechromotrope, 4,4'-sulphonyl-bis(azobenzene) dichromotropic acid.     

Cation-exchange chromatography of some metal ions using aqueous NH4SCN-organic solvent mixtures

Summary Systematic cation-exchange studies of 19 metal ions have been made in various concentrations of NH₄SCN in 4060 organic solvent-water mixtures. The exchange behaviour of the ions depends on the solvent employed. Most of the metal ions show decreasing distribution coefficients with increasing concentration of ammonium thiocyanate in the solvent. Based on the variation of distribution coefficients as a function of NH₄SCN concentration, separations could be predicted and subsequently column chromatographic separations involving Zn, Hg(II), Mg, Mn(II), Co(II), Ni(II), Cd(II), Ce(III), Fe(III), La and Th(IV) were achieved.     

Complexometric determination of cadmium using 2-Mercaptoethanol as masking reagent

A complexometric method for the determination of cadmium(II) in presence of other metal ions is described based on the selective masking ability of 2-mercaptoethanol towards cadmium(II). Cadmium and other ions in a given sample solution are initially complexed with excess of EDTA and the surplus EDTA is titrated with lead nitrate solution at pH 5.0–6.0 (hexamethylentetramine), using xylenol orange as indicator. A known excess of 2-mercaptoethanol solution (10% alcoholic) is then added, the mixture is shaken well and the released EDTA from the Cd-EDTA complex is titrated against standard lead nitrate solution. The interferences of various ions are studied and the method is applied to the determination of cadmium in its complexes. Reproducible and accurate results are obtained for 3.5–25mg of Cd with relative errors 0.65% and standard deviations 0.06 mg.     

Complexometric determination of gallium with calcein blue as indicator

A metalfluorechromic indicator, Calcein Blue, has been used for the back-titration of milligram amounts of EDTA in presence of gallium complexes. The indicator was used in conjunction with an ultraviolet titration assembly equipped with a cadmium sulphide detector cell and a microammeter for enhanced end-point detection. The result is a convenient and rapid method with an accuracy approaching 0.1% and a relative standard deviation of about 0.4% for 10 mg of gallium.     

Complexometric determination of mercury(II) using Congo Red as indicator

Congo Red is suggested as an indicator for the direct titration of mercury(II) ions with EDTA or with potassium thiocyanate. An interference study of a number of cations has been made. The titration with thiocyanate is more advantageous than that with EDTA.     

Kinetic determination of trace cobalt(II) by visual autocatalytic indication

A highly sensitive and simple visual autocatalytic method has been developed for the determination of trace cobalt. The cobalt ion released by the oxidative decomposition of inert bis[2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropyl-amino-phenolato] cobaltate (Co(III)-5-Br-PAPS) with peroxomonosulfate acts as a catalyst for the oxidative degradation of the complex. Thus a definite time lapse of degradation is observed by the sudden disappearance of colored Co(III) complexes. The degradation time varies inversely with the logarithm of the initial concentration of cobalt(II). The determination range of cobalt(II) was from 3x10(-9) to 2x10(-7) M in the presence of 5x10(-6) M of 5-Br-PAPS. The relative standard deviation of the spot size method (10 mul) was 3.5% at 1x10(-7) M cobalt(II). This autocatalytic indicator reaction system has been successfully applied for the visual determination of urinary cobalt.     

Separation and determination of some trivalent metal ions using rhodamine B grafted polyurethane foam

The incorporation of rhodamine B into polyurethane foam matrix was prepared by mixing the rhodamine B with polyol (polyether) prior to the addition of diisocyanate reagent to form the polyurethane foam material. Rhodamine B grafted polyurethane foam (Rod.B-PUF) was found to be very suitable for the separation and preconcentration of trivalent metal ions e.g. bismuth (III), antimony (III) and iron (III) from thiocyanate solutions. Bismuth and antimony were separated from concentrated acid medium (1–6 M H₂SO₄). Iron (III) was separated from pH 1 to 3. The kinetics of sorption of the Bi (III), Sb (III) and Fe (III) onto the Rod.B-PUF was found to be fast, the extraction is accomplished from 5 to 10 min with average values of half-life of sorption (t_1/2) of 2.9 min. The average values of the Gibbs free energy (ΔG) for the sorption of metal ions onto Rod.B-PUF are ?6.6 kJ mol^?1, which reflect the spontaneous nature of sorption process. The sorption mechanism of the metal ion onto Rod.B-PUF was also discussed.     

Complexometric determination of molybdenum(VI)

In acidic medium molybdenum(VI) forms a stable complex on boiling with excess of DCTA and hydroxylamine hydrochloride. Molybdenum can then be determined by back-titration of the excess of DCTA either with zinc chloride at pH 5-5.5 or with thorium nitrate at pH 3-4.5, Xylenol Orange being used as indicator in both cases. A simple method for the determination of molybdenum in the presence of moderate amounts of tungsten is also described.     

Differential spectrophotometric determination of micro amounts of metal ions in mixtures

A differential spectrophotometric method is described for the simultaneous determinations of iron and molybdenum, iron and titanium, iron and uranium, molybdenum and titanium, and molybdenum and uranium in mixtures, in a single solution at room temperature. The general method consists in treating the mixture with 5 ml of 1 M sodium acetate and 1 ml of 1% pyrocatechol in 25-ml volumetric flasks. The optical density of color of mixed complexes is determined at the corresponding pair of wavelengths suggested. From the optical density and molar extinction coefficient, the concentration of each ion in mixtures has been calculated. By this procedure, the metal ions can be determined even if they differ by large ratios. Procedures have been extended for the analysis of mixtures containing iron, molybdenum, and titanium (or uranium). These procedures can be applied for the analysis of any type of materials, like minerals, rocks, ores, alloys, steels and refractory materials. Spectra of each complex and their Beer's law were studied in detail. Experiments were also made to show that the calculated and observed optical density of mixture complexes is the same, thereby the additive of optical density of mixtures at each pair of wavelengths suggested for individual determinations of ions have been verified.     

Simultaneous determination and validation of some binary mixtures of antihypertensive drugs using ratio derivative spectrophotometric method

Ratio derivative spectrophotometric technique is presented for the rapid, accurate and precise simultaneous determination of olmesartan medoxomil (OLM), hydrochlorothiazide (HCT), and zofenopril (ZOF) as well as HCT binary mixtures in their dosage forms. First derivative of the ratio spectra (DD1) by measurements using different amplitudes was used and calibration graphs were established for 0.5–12 mg/mL HCT and 0.5–20 mg/mL OLM and ZOF. This method depends on first derivative of the ratio spectra by division of the absorption spectrum of the binary mixture by a standard spectrum of one of the components and then calculating the first derivative of the ratio spectrum. The first derivative of the ratio amplitudes at 250.4 and 291.5 nm for OLM, 250.4 and 298.1 nm for ZOF and 231.8, 332.2, 232.3 and 280.4 nm for HCT were selected for the determination. The proposed methods were successfully applied for determining of both drug combinations (ZOF-HCT and OLM-HCT) in their synthetic mixtures and in pharmaceutical dosage forms. The described procedures are extensively validated, non-destructive and do not require any separation steps.     

Complexometric determination of palladium(II) using thioacetamide as a selective masking agent

A simple, rapid and accurate complexometric method for the determination of palladium(II) is proposed, based on the selective masking property of thioacetamide towards palladium(II). In the presence of diverse metal ions, palladium(II) is complexed with excess of EDTA and the surplus EDTA is back titrated at pH 5-5.5 (acetic acid-sodium acetate buffer) with standard lead nitrate solution using xylenol orange as indicator. An excess of a 0.5% aqueous solution of thioacetamide is then added to displace EDTA from Pd(II)-EDTA complex. The released EDTA is titrated with the same standard lead nitrate solution as before. Reproducible and accurate results are obtained in the concentration range 0.5 mg - 17.80 mg of palladium with relative error of +/- 0.16% and coefficient of variation not exceeding 0.26%. The effect of diverse ions is studied. The method is used for the determination of palladium in its complexes, catalysts and synthetic alloy mixtures.     

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.

     

Simultaneous spectrophotometric determination of Fe and Ni with xylenol orange using principal component analysis and artificial neural networks in some industrial samples

Artificial neural networks (ANNs) are among the most popular techniques for nonlinear multivariate calibration in complicated mixtures using spectrophotometric data. In this study, Fe and Ni were simultaneously determined in aqueous medium with xylenol orange (XO) at pH 4.0. In this way, after reducing the number of spectral data using principal component analysis (PCA), an artificial neural network consisting of three layers of nodes was trained by applying a back-propagation learning rule. Sigmoid transfer functions were used in the hidden and output layers to facilitate nonlinear calibration. Adjustable experimental and network parameters were optimized, 30 calibration and 20 prediction samples were prepared over the concentration ranges of 0-400 mug l(-1) Fe and 0-300 mug l(-1) Ni. The resulting R.S.E. of prediction (S.E.P.) of 3.8 and 4.7% for Fe and Ni were obtained, respectively. The method has been applied to the spectrophotometric determination of Fe and Ni in synthetic samples, some Ni alloys, and some industrial waste waters.     

Formation of orange oil-in-water nanoemullsions using nonionic surfactant mixtures by high pressure homogenizer

The formation of nanoemulsions depends on the size of the droplets formed, the polydispersity and the difference in solubility and/or chemical potential between the small and large droplets. This article reports experiments to evaluate the formation of orange oil/water nanoemulsions in the presence of mixtures of nonionic surfactants, prepared in a high-pressure homogenizer. The surfactant mixtures were prepared to have different HLB values, by varying their type and concentration. The formation and stability of the nanoemulsions were evaluated as a function of the surfactant mixture used and also the processing conditions in the homogenizer. The size and distribution of the droplets formed, along with their stability, were determined in a Zetasizer Nano ZS particle size analyzer. The results showed that the optimal HLB range of the surfactant mixtures to obtain stable o/w nanoemulsions, independent of the processing conditions, is between 11 and 12. Better results were obtained with Unitol®L20/Unitol®L100 mixtures, in which the hydro-phobic surfactant causes a reduction in the interfacial tension and the hydrophilic surfactant promotes steric stabilization of the system.