Sequential injection technique employed for stoichiometric studies, optimization and quantitative determination of some fluoroquinolone antibiotics complexed with iron(III) in sulfuric acid media

A sequential injection spectrophotometric method for stoichiometric studies, optimization and quantitative determination of ciprofloxacin and norfloxacin was developed. The work is based on the complexation reaction of ciprofloxacin and norfloxacin with iron(III) in sulfuric acid media and a spectrophotometric measurement of absorbances of the corresponding complexes at 447 and 430 nm respectively. The stoichiometries and formation constants were determined. A 1:2 iron(III) to drug mole ratio was found to give the most predominant complexes for both drugs with 5.00 x 10(-3) M H(2)SO(4) and at 0.20 M ionic strength utilizing Job's method and the molar ratio method. A numerical method was utilized for the calculation of the formation constants, the logarithms of which were found to be 7.756 +/- 0.121 and 7.839 +/- 0.056, for ciprofloxacin and norfloxacin respectively. A factorial design together with the all-model-search method was utilized for the optimization of the concentration and aspiration volume of iron(III) as these were the variables which most affected peak absorbance. Working dynamic ranges of 50-500 ppm and 50-400 ppm were obtained for ciprofloxacin and norfloxacin respectively. The method was found to be suitable for the determination of these compounds in pharmaceutical preparations.     

Sequential Injection Method for the Determination of Oxprenolol in Pharmaceutical Products Using Chemometric Methods of Optimization

A sequential injection (SI) spectrophotometric method for the determination of oxprenolol in pharmaceutical products was developed. The method is based on the oxidation of oxprenolol on-line with Ce(IV) in sulfuric acid medium and the subsequent monitoring of the absorbance of the oxidized form of the drug at 480 nm. The procedure was optimized by the orthogonal array design at two and four levels. The factors included in the optimization were Ce(IV) concentration, sulfuric acid concentration, and the stop time of the composite zone at the reaction coil. The optimized SI system with a linear dynamic range of 50–400 ppm was found to be suitable for the assay of oxprenolol in pharmaceutical products.     

Enhancement of the chemiluminescence of penicillamine and ephedrine after derivatization with aldehydes using tris(bipyridyl)ruthenium(II) peroxydisulfate system and its analytical application

A novel sequential injection (SI) method was developed for the determination of penicillamine (PA) and ephedrine (EP) based on the reaction of these drugs with tris(bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) and peroxydisulfate (S₂O₈²⁻) in the presence of light. Derivatization of PA and EP with aldehydes has resulted in a significant enhancement of the chemiluminescence emission signal by at least 25 times for PA and 12 times for EP, leading to better sensitivities and lower detection limits for both drugs. The instrumental setup utilized a syringe pump and a multiposition valve to aspirate the reagents, (Ru(bpy)₃²⁺ and S₂O₈²⁻), and a peristaltic pump to propel the sample. The experimental conditions affecting the derivatization reaction and the chemiluminescence reaction were systematically optimized using the univariate approach. Under the optimum conditions linear calibration curves between 0.2–24 μg mL⁻¹ for PA and 0.2–20 μg mL⁻¹ for EP were obtained. The detection limits were 0.1 μg mL⁻¹ for PA and 0.03 μg mL⁻¹ for EP. The procedure was applied to the analysis of PA and EP in pharmaceutical products and was found to be free from interferences from concomitants usually present in these preparations.     

Studies on the reaction of N‐(3‐carbethoxy‐4,5,6,7‐tetrahydrobenzo[b]thien‐2‐yl)‐N′‐phenylthiourea with hydrazine hydrate (Part 1)

The reaction of N‐(3‐carbethoxy‐4,5,6,7‐tetrahydrobenzo[b]thien‐2‐yl)‐N′‐phenylthiourea ( 1 ) with hydrazine hydrate in 1‐butanol afforded a mixture of compounds 2, 3 and 4 . Treatment of 3 and 4 with nitrous acid gave 6 and 8 respectively, while reactions of 3 with acetylacetone gave 7 . Synthesis of tetracyclic compounds 9a‐f and 11 from the reactions of 3 with ethyl orthoformate or appropriate acids, acid chloride, carbon disulphide and/or ethyl chloroformate. Also its reaction with isothiocyanate derivatives gave the corresponding thiosemicarbzides 12a,b which on, refluxing in alcoholic KOH gave the unexpected tetracyclic products 14a,b . Similarly the tetracyclic compounds 16a‐e and 19 were obtained by cyclization of 4 and 18 respectively.     

Fluorescence enhancement of coumarin-6-sulfonyl chloride amino acid derivatives in cyclodextrin media.

Coumarin-6-sulfonyl (6-CS) amino acid derivatives form inclusion complexes with a- and /-cyclodextrins (CD) in aqueous solution. The stoichiometry of the inclusion complex and the equilibrium constant were investigated. Using a fluorescence technique and alanine-beta-CD as a model, a 1:2 guest-host complex was established, and K = 4.7 x 10(5) mol(-2) l(2) was obtained. Fluorescence enhancement was observed for all derivatives studied, with glycine exhibiting a greater enhancement, and tyrosine showing the least. The stability of the inclusion complex was found to depend on the respective sizes of the guest-host complex and their interaction.     

Semidefinite programming for the educational testing problem

Methods for solving the educational testing problem which arises from statistics are considered. The problem is to find lower bounds for the reliability of the total score on a test (or subtests) whose items are not parallel using data from a single test administration. We formulate the problem as an optimization problem with a linear objective function and semidefinite constraints. We maintain exact primal and dual feasibility during the course of the algorithm. The search direction is found using an inexact Gauss–Newton method rather than a Newton method on a symmetrized system. Computational results illustrating the robustness of the algorithm are successfully exploited. Research supported by King Fahd University of Petroleum and Minerals under Project FT/2005–2007.     

Noncoercive mixed equilibrium problems under pseudomonotone perturbations and applications to nonlinear evolution equations with lack of coercivity

In this paper, we study the existence of solutions for noncoercive mixed equilibrium problems which are described by the sum of a maximal monotone bifunction and a pseudomonotone (or quasimonotone) bifunction in the sense of Brézis. Our approach is based on recession analysis and on recent results established by the authors for the existence of solutions of mixed equilibrium problems under pseudomonotone perturbations. As an application, we study the existence of solutions for nonlinear evolution equations associated with a noncoercive time-dependent pseudomonotone (or quasimonotone) operator.     

Capillary electrophoretic separation and computational modeling of inclusion complexes of β‐cyclodextrin and 18‐crown‐6 ether with primaquine and quinocide

The antimalarial drug primaquine (PQ) and its contaminant, the positional isomer quinocide (QC) have been successfully separated using capillary electrophoresis with either β‐cyclodextrin (β‐CD) or 18‐crown‐6 ether (18C6) as chiral mobile phase additive. The interactions of the drugs with cyclodextrins and 18C6 were studied by the semiempirical method (Parametric Model 3) PM3. Theoretical calculations for the inclusion complexes of PQ and QC with α‐CD, β‐CD and 18C6 were performed. Data from the theoretical calculations are correlated and discussed with respect to the electrophoretic migration behavior. More stable complexes are predicted for the PQ–β‐CD and PQ–18C6 complexes. The coelution of PQ and QC when α‐CD was used as buffer additive can be explained by their comparable stabilities of the inclusion complex formed, while significant differences in the complexation stabilities of the drugs with β‐CD is responsible for their separation. The stronger hydrogen bonding in PQ–18C6 system is responsible for the separation between PQ and QC when 18C6 was used as chiral mobile phase additive. Copyright © 2009 John Wiley & Sons, Ltd.