Spectrophotometric assay of cephalosporins in pharmaceutical products,using chromotrope 2B and chromotrope 2R

A simple, rapid and sensitive Spectrophotometric method is proposed for the determination of cephadroxil (I), cephalexin (II) and cephradine (III). The method is based on ion-pair complex formation between these derivatives and Chromotrope 2B (C2B) or Chromotrope 2R (C2R), to give a highly coloured radical anion. The coloured products are quantified spectrophotometrically at 542 and 564 nm for C2B and C2R, respectively. The optimization of the experimental conditions is described. The method has been used for the determination of 0.4–15, 0.4–14 and 0.4–18 g/ml of drugs I, II and III, respectively. The accuracy of the method is indicated by the excellent recovery (100.0±1.7%) and the precision is supported by the low relative standard deviations 1.5%. The sensitivity of the method is discussed and the results are compared with the official method. The interference from common degradation products and excipients was also studied. The proposed method was applied successfully to the determination of the different cephalosporins in dosage forms, with good precision and accuracy. The results were compared with those given by the official B.P. 1993 method.     

Synthesis and Dynamic NMR Study of Functionalized 1-(3-Furyl)-1H-indole-2,3-diones

Protonation of the highly reactive 1:1 intermediates produced in the reaction between alkyl(aryl) isocyanides and dibenzoylacetylene by isatin, leads to vinylnitrilium cations, which undergo carbon-centered Michael-type addition with the conjugate base of the NH-acid to produce highly functionalized 1-(3-furyl)-1H-indole-2,3-diones. A dynamic NMR effect is observed in the ¹H NMR spectra of these compounds as a result of restricted rotation around the single bond linking the indole moiety and the furan system. The free-energy of activation (ΔG ^#) for this process is 69–71 ± 2 kJ mol⁻¹.     

Spectrophotometric determination of palladium using arsenazo I

A new simple rapid method for the spectrophotometric determination of palladium using arsenazo I is given. The optimum conditions favoring the formation of the complex are extensively investigated; the molecular structure was found to be 1:1. Beer's law is obeyed for the ranges 1.0–10.6 or 0.64–6.39 ppm of Pd.     

Carbon Paste Electrode for the Potentiometric Flow Injection Analysis of Drotaverine Hydrochloride in Serum and Urine

A carbon paste electrode for drotaverine hydrochloride (DvCl) was prepared and fully characterized in terms of composition, life span, usable pH range, response time and temperature. The electrode was applied to the potentiometric determination of drotaverinium ions in pharmaceutical preparations and biological fluids in steady state and flow injection conditions (FIA). The electrode is based on a mixture of two ion exchangers, namely, drotaverinium-silicotungestate and drotaverinium-tetraphenylborate dissolved in tricresyl phosphate as pasting liquid. The modified electrode showed a near-Nernstian slope of 59.34±2mV over the concentration range of 5.0×10^–7–1.0 × 10^–2M. The electrode exhibits good selectivity for DvCl with respect to a large number of inorganic cations, organic cations, sugars and amino acids. Potentiometric titrations of DvCl with several titrants have been monitored using this modified carbon paste electrode as an end-point indicator electrode. The proposed electrode offers the advantages of simplicity, accuracy, automation feasibility and applicability to turbid and colored samples.     

Application of Alizarine Derivatives as Chromogenic Reagents for the Spectrophotometric Determination of Some Sulfa Drugs

A spectrophotometric procedure for the determination of six pharmaceutical sulfonamides containing a primary aromatic amino group using alizarine (I), alizarine blue (II), alizarine red (III), and quinalizarine (IV), that offers advantages of simplicity, rapidity, sensitivity, precision, and stability, has been developed. The proposed method is based on the formation of colored products with the chromogenic reagents (I-IV). A linear correlation was found between absorbance at λ_max and the concentration. For more accurate results, Ringbom optimum concentration ranges are evaluated. The molar absorptivities (ε), absorptivities (a), and Sandell sensitivities for all sulfonamides derivatives with the chromogenic reagents tested were calculated. The procedures developed are applied for bulk sulfa drugs and some of their dosage forms.     

A synthesis of pyrrolo[2,1-a]isoquinolines through the reaction of activated acetylenes and isoquinoline in the presence of ethyl bromopyruvate

Isoquinoline reacts with ethyl bromopyruvate in the presence of dialkyl acetylenedicarboxylates or diaryloylacetylenes to produce dialkyl 1-(2-ethoxy-2-oxoacetyl)pyrrolo[2,1-a]isoquinoline-2,3-dicarboxylates or ethyl 2-[2,3-diaryloylpyrrolo[2,1-a]isoquinoline-1-yl]-2-oxoacetates in good yields.     

Oxidations with alkaline permanganate using monovalent thallium for the back-titration: Determination of iodate,iodide and ferrocyanide

Iodate, iodide, iodine and ferrocyanide can be estimated by oxidation with KmnO₄ in alkaline media; the excess is back-titrated with TI⁷. I^- and I₂ are oxidized to IO₄^- in the presence of Ba⁺² ions but only to IO₃^- in absence of such ions. The direct titration of IO₃^-, I^- with KmnO₄ proved valueless.Ferrocyanide is oxidized by KmnO₄ in alkaline solutions and MnO₂ is formed. In the presence of telluric acid and 0.025–0.1 N NaOH satisfactory results are obtained. Reduction of MnO₄^- with ferrocyanide gives MnO₄^-2 and the results are variable, depending on the rate of adding the ferrocyanide.     

Influence of solvent polarity and medium acidity on the UV-Vis spectral behavior of 1-methyl-4-[4-amino-styryl] pyridinum iodide

Electronic absorption, and excitation spectra of 1-methyl-4-[4-aminostyryl] pyridinum iodide (M-NH2) were measured in solvents of different polarity. The (M-NH2) dye exhibits negative solvatochromism, i.e. a hypsochromic band shift as the solvent polarity increases. The fluorescence quantum yield is also sensitive to the polarity and viscosity of the medium. The ground and excited state protonation constants were calculated and amount to 3.35 and 0.62, respectively. The effect of micellization on the emission spectrum of (M-NH2) are also studied in sodium dodecyl sulphate (SDS). The fluorescence intensity increases as the concentration of SDS increases with an abrupt change at cmc. The quantum yield of the cis trans photoisomerization is also determined in aqueous buffer solution of pH 1.1.     

A new synthesis of highly functionalized 2H-pyran derivatives

Ethyl oxo-(2-oxo-cycloalkyl)-ethanoates undergo a smooth reaction with triphenylphosphine and dialkyl acetylenedicarboxylates via intramolecular Wittig reaction to produce spiro-cyclobutene derivatives. These spiro systems undergo electrocyclic ring opening reaction to produce electron-deficient 1,3-dienes, which spontaneously cyclize to 2H-pyran derivatives.