Spectrophotometric determination of H(2)-receptor antagonists via their oxidation with cerium(IV)

A simple, accurate and sensitive spectrophotometric method has been developed and validated for determination of H(2)-receptor antagonists: cimetidine, famotidine, nizatidine and ranitidine hydrochloride. The method was based on the oxidation of these drugs with cerium(IV) in presence of perchloric acid and subsequent measurement of the excess Ce(IV) by its reaction with p-dimethylaminobenzaldehyde to give a red colored product (lambda(max) at 464nm). The decrease in the absorption intensity of the colored product (DeltaA), due to the presence of the drug was correlated with its concentration in the sample solution. Different variables affecting the reaction were carefully studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients (0.9990-0.9994) were found between DeltaA values and the concentrations of the drugs in a concentration range of 1-20microgml(-1). The assay limits of detection and quantitation were 0.18-0.60 and 0.54-1.53microgml(-1), respectively. The method was validated, in terms of accuracy, precision, ruggedness and robustness; the results were satisfactory. The proposed method was successfully applied to the determination of the investigated drugs in pure and pharmaceutical dosage forms (recovery was 98.3-102.6+/-0.57-1.90%) without interference from the common excipients. The results obtained by the proposed method were comparable with those obtained by the official methods.     

Spectrophotometric determination of cerium(IV) with tetraethylenepentaamineheptaacetic acid (TPHA)

Tetraethylenepentaamineheptaacetic acid (TPHA) combines with cerium(IV) to form an intensely yellow chelate having a molar absorptivity of 4.5 × 10⁴ mol⁻¹ · cm⁻¹ · liter at 304 nm. The chelate contains 1 mol of TPHA coordinated to a cerium(IV) atom. Beer's law is followed from 0.05 to 0.5 ppm cerium (1.00-cm cells). Of many ions tested at the 1-ppm level and the 100-ppm concentration, only iron(III) produces little interference.     

Spectrophotometric determination of cerium(IV) using a phenothiazine derivative.

A simple, rapid and sensitive spectrophotometric method has been proposed for the determination of cerium(IV) using a phenothiazine derivative, propionyl promazine phosphate (PPP). This method is based on the formation of a red-colored radical cation upon a reaction of PPP with cerium(IV) in a phosphoric acid medium having maximum absorbance at 513 nm. Beer's law is valid over the concentration range of 1-11 microg/ml with a Sandell's sensitivity value of 16.14 ng/cm2. The proposed method has been successfully applied to the analysis of magnesium-base cerium alloys and synthetic mixtures corresponding to various cerium alloys. Other phenothiazine derivatives viz. butaperazine dimaleate and propericiazine were also used for the determination of cerium(IV).     

Titrimetric determination of octacyanotungstate(IV) ions with N-bromosuccinimide

Summary N-Bromosuccinimide has been successfully applied in the determination of 1–50 mg of W(CN)₈ ^4–in approximately 6 M hydrochloric acid using Naphthol Blue Black indicator. The average error is ±0.42% and the average standard deviation is ±0.06 mg. The method is not applicable to the determination of Mo(CN) ₈ ^4– ions. Tetrakis-(N-hydro-2-carbocyclic acid-pyridinium)octacyanotungstate(IV) and -molybdate(IV) were used as primary standards for the preparation of standard Mo(IV) and W(IV) solutions. The composition of the latter compounds was verified by analysis and single crystal X-ray data were obtained.

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Titrimetrische Bestimmung von Octacyanowolframat(IV)-ionen mit N-Bromsuccinimid

Zusammenfassung N-Bromsuccinimid wurde mit Erfolg zur Bestimmung von 1–50 mg W(CN)₈ ^4–-Ionen in ungefähr 6 M Salzsäure mit Naphthol-Blau-Schwarz als Indicator verwendet. Der mittlere Fehler beträgt ±0,42 %, die mittlere Abweichung ±0,06 mg. Die Methode ist nicht brauchbar für die Bestimmung von Mo(CN)₈ ^4–-Ionen. Tetrakis(N-hydro-2-carbonylsäure-pyridinium) octacyanowolframat(IV) und -molybdat(IV) wurden als Primärstandards für die Herstellung von Standard-Mo(IV)- und -W(IV)-Lösungen benutzt. Die Zusammensetzung dieser Verbindungen wurde durch Analyse kontrolliert und die Einkristall-Röntgen-Daten wurden festgestellt.

     

Spectrofluorometric determination of ketorolac tromethamine via its oxidation with cerium(IV) in pharmaceutical preparations and biological fluids

A simple and sensitive fluorometric method for determination of ketorolac tromethamine was studied. The method depends on oxidation of the drug with cerium(IV) and subsequent monitoring of the fluorescence of the induced cerium(III) at lambda(em) 365 nm after excitation at 255 nm. Different variables affecting the reaction conditions, such as the concentrations of cerium(IV), sulfuric acid concentration, reaction time, and temperature, were carefully studied and optimized. Under the optimum conditions, a linear relationship was found between the relative fluorescence intensity and the concentration of the investigated drug in the range of 0.1-0.8 microg/mL. No interferences could be observed from the excipients commonly present in dosage forms. The proposed method was successfully applied to the analysis of the investigated drug in its pure form, pharmaceutical preparations, and biological fluids with good accuracy and precision. The recoveries for pharmaceutical formulations ranged from 99.8-101.0 +/- 0.6% for tablets, 98.5-101.0 +/- 1.0% for ampoules, and 99.0-100.5 +/- 0.7% for eye drops. The results obtained by the proposed method were satisfactory compared with those obtained by the official method. The recoveries for biological fluids were 99.1-100.4 +/- 0.7 and 99.0-100.0 +/- 0.5% for plasma and urine, respectively.     

Kinetics of the oxidation of oxalic acid by cerium(IV) sulfate in dilute sulfuric acid

The kinetics of the oxidation of oxalic acid by cerium(IV) in sulfuric acid medium has been studied voltammetrically. The specific reaction rate is 132±4.0 M^–1s^–1 at 25.0 °C. The energy of activation is 62.6±3.0 kJ mol^–1. The entropy of activation is –2.7 J mol^–1K^–1. The specific reaction rate is influenced by complexation and also by ionic strength (). The most likely mechanism has been suggested.

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(IV) . 132±4,0 M^–1c^–1 25,0 °C. 62,6±3,0 ·M^–1. –2,7 ·K^–1M^–1. , (). .

     

Spectrophotometric determination of cerium(IV), arsenic(III), and nitrite with promazine hydrochloride

Promazine hydrochloride is proposed as a new reagent for the spectrophotometric determination of cerium(IV), arsenic(III), and nitrite. The reagent forms a red-colored radical with cerium(IV) instantaneously in 0.5?2 M sulfuric acid or 0.5?2.5 M phosphoric acid solution. The red radical exhibits maximum absorbance at 505 nm. An 11-fold molar excess of the reagent is necessary for the full development of the color intensity. Beer's law is valid over the concentration range 0.5–15 ppm in sulfuric acid and 0.5–21 ppm in phosphoric acid. The sensitivities of the reaction in sulfuric and phosphoric acid media are 0.022 and 0.019 μg/cm², respectively. The effects of acidity, time, order of addition of reagents, temperature, reagent concentration, and diverse ions are reported. The proposed method offers the advantages of good sensitivity, simplicity, rapidity, selectivity, and a wider range of determination without the need for extraction. Arsenic(III) and nitrite are indirectly determined.     

Continuous-flow chemiluminescence determination of isoniazid by oxidation with N-bromosuccinimide

A rapid and precise continuous-flow method is described for the determination of isoniazid (0.050-20.0 micrograms ml(-1)) based on the chemiluminescence produced during its reaction with N-bromosuccinimide in alkaline medium. The emission intensity is greatly enhanced by the presence of ammonia. The procedure is automated and samples can be analysed at a rate of 112 solutions per hour with a relative error of about 2%. When applied to tablets, the method is relatively free from interferences from common excipients and co-existing compounds. The results obtained for the assay of commercial preparations compared well with those obtained by an official chemical method and demonstrated good accuracy and precision.     

Simultaneous spectrofluorimetric determination of cerium(III) and cerium(IV) by flow injection analysis

Cerium(III) (1–100 μg l^?1) is determined by injection into a carrier stream of hydrochloric, perchloric or sulphuric acid, and monitoring its native fluorescence. Cerium(IV) can be determined similarly by incorporating a zinc reductor minicolumn into the system. Splitting the injection sample so that only part passes through the reductor, and the remainder by-passes it, allows total cerium and cerium(III) to be detected from the two sequential fluorescence peaks obtained.     

Indirect spectrophotometric determination of cerium(IV)

A simple and very fast photometric method for the determination of trace levels of cerium(IV) has been developed. Use has been made of the reaction in which iron (II), on oxidation with cerium(IV), gives iron(III) which is complexed with tiron, in acidic medium, to form a stable blue color, the intensity of which is in direct proportion to the amount of cerium(IV) originally present in the sample solution. In addition, the method has a wide range of determination and reasonable sensitivity, and it avoids both temperature control and the tedious extraction step.     

Kinetics and mechanism of ruthenium(III) catalyzed oxidation of tellurium(IV) by cerium(IV)

The reaction is zero order in cerium(IV), fractional order in tellurium(IV) and first oder in ruthenium(III). While the ionic strength has no effect, the rate increases with increasing [H⁺], and decreases with increasing [HSO ₄ ^– ]. H and S are 54.4 kJ mol^–1 and –60.3 JK^–1 mol^–1, respectively. A suitable mechanism is proposed.

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(IV), (IV) (III). , [H⁺] [HSO ₄ ^– ]. H S 54,4 ^–1 –60,3 ·^–1·^–1, . .