Simultaneous determination of ofloxacin,tetrahydrozoline hydrochloride,and prednisolone acetate by high-performance liquid chromatography

A simple, specific, and precise high-performance liquid chromatographic method has been developed for the simultaneous determination of ofloxacin (OFX), tetrahydrozoline hydrochloride (THC), and prednisolone acetate (PAC) in ophthalmic suspension using propylparaben (POP) as the internal standard. The mobile phase consists of 0.05 M phosphate buffer-acetonitrile (65:35, v/v), and the pH is adjusted to 2.7 with orthophosphoric acid. A column containing octadecyl silane chemically bonded to porous silica particles (Waters Spherisorb, 5 microm ODS 1, 4.6 x 150 mm) is used as the stationary phase. The detection is carried out using a variable wavelength UV-vis detector set at 210 nm for OFX and THC and 254 nm for POP (internal standard) and PAC. The solutions are chromatographed at a constant flow rate of 1.2 mL/min. Retention times for OFX, THC, POP, and PAC are approximately 2.5, 4.5, 7.8, and 9.5 min, respectively. The relative retention times are approximately 0.14 min for OFX, 0.35 min for THC, 1.00 min for POP, and 1.22 min for PAC. The linearity range and percent recoveries for OFX, THC, and PAC are 24-120, 4-16, and 16-80 microg/mL and 100.48%, 100.34%, and 100.21%, respectively.     

Adsorption characteristics and the kinetics of the cation exchange of rhodamine-6G with Na+-montmorillonite

The adsorption and the kinetics of the cation exchange of rhodamine-6G (Rh-6G) with Na(+)-montmorillonite (Na(+)-MMT) have been studied. The binding parameters of Rh-6G have been determined by applying Freundlich and D-R isotherms. The enthalpy and the entropy of adsorption have been determined. The isosteric heat of adsorption has also been determined and decreases with increasing the concentration of Rh-6G. Increasing the concentration of Rh-6G led to a decrease in the adsorption capacity, which attributed to the formation of Rh-6G aggregates. Kinetic measurements of the cation exchange were followed up using a stopped-flow electrical conductivity detection unit. The cation-exchange process exhibited first-order kinetics with respect to the dye concentration and inversely proportional to the clay concentration. The measurements were accomplished at different temperatures and the activation parameters were determined. Increasing the Na(+)-MMT concentration led to a decrease in the rate constant. The latter is also affected by changing the exchangeable cation.     

Cobalt determination with FI-FAAS after on-line sorbent preconcentration using 1-nitroso-2-naphthol

The suitability of 1-nitroso-2-naphthol (NN) as a complexing agent for on-line preconcentration of cobalt using C(18) microcolumn with FI-FAAS system has been tested. Various parameters affecting the complex formation and its elution were optimized. Reagent solution (2.5x10(-3) mol l(-1)) and aqueous sample solution acidified with 0.1% (v/v) nitric acid were on-line mixed in a reaction coil set at 65+/-1 degrees C and flowed through the microcolumn for 30 s. The pH of the mixed solution was adjusted to 3 approximately 4 by adding HNO(3) (1 mol l(-1)) or NaOH (1 mol l(-1)) in the reagent solution. The adsorbed complexes in the microcolumn were eluted with ethanol (acidified to 1% nitric acid) in 10 s into the nebulizer of FAAS. A good precision (1.6% for 100 mug l(-1) Co(II), n=10), high enrichment factor 17.2, with detection limit (3sigma) 3.2 mug l(-1), and sample throughput (90 h(-1)) were obtained. The method was applied on the certified reference materials (CRMs) i.e. NBS-362 and NBS-364 (special low alloy steel), for the determination of cobalt and the results were in good agreement with the certified values.     

A dithienylethene-tethered beta-cyclodextrin dimer as a photoswitchable host

The binding of TSPP by a dithienylethene-tethered beta-cyclodextrin dimer can be altered reversibly by irradiation with light.     

A convergent approach to 3-substituted-5-methoxyindoles. Application to the synthesis of melatonin [correction

A convergent, radical based synthesis of 5-methoxyindoles including melatonin is described.     

One-step SFE-plus-C(18) selective extraction of low-polarity compounds,with lipid removal,from smoked fish and bovine milk

Co-extraction of lipid materials is the major source of interference in determinations of low-polarity compounds in many biological matrixes. "SFE-plus-C(18)", a recently developed supercritical fluid extraction method employing C(18) adsorbent in the extraction chamber, can enable selective extraction of low-polarity compounds in lipid-rich biological matrixes without a cleanup step. This study reports the application of the SFE-plus-C(18) method to the quantification of: 1. polycyclic aromatic hydrocarbons (PAH) in commercially purchased smoked fish; and 2. anti-cancer agents cyclophosphamide (CP) and suberoylanilide hydroxamic acid (SAHA) spiked into homogenized whole bovine milk.Over the course of SFE-plus-C(18)extraction, indigenous lipids are preferentially retained on the C(18) adsorbent. Compared with the conventional method, only 8-15% of the lipids in the smoked fish sample, and only 6-18% of the lipids in the milk sample, were co-extracted by SFE-plus-C(18). This reduction in the quantity of background lipids significantly improved chromatographic separations, retarded deterioration of the column, and dramatically improved the ability to quantify PAH present at trace levels in smoked fish by GC-MS. Using the SFE-plus-C(18) method, ten targeted PAH were detected in the range 9.5-13.5 ng g(-1) in the smoked fish sample. Compared with these levels, PAH extractions by use of conventional SFE gave values that were lower by 38-86%. Recoveries of CP and SAHA spiked into milk were close to 100% in both SFE-plus-C(18)and conventional SFE, where the lipid background during the chromatographic elution of CP and SAHA was not so severe.     

Evidence for nearby supernova explosions

Supernova (SN) explosions are one of the most energetic---and potentially lethal---phenomena in the Universe. We show that the Scorpius-Centaurus OB association, a group of young stars currently located at approximately 130 pc from the Sun, has generated 20 SN explosions during the last 11 Myr, some of them probably as close as 40 pc to our planet. The deposition on Earth of (60)Fe atoms produced by these explosions can explain the recent measurements of an excess of this isotope in deep ocean crust samples. We propose that approximately 2 Myr ago, one of the SNe exploded close enough to Earth to seriously damage the ozone layer, provoking or contributing to the Pliocene-Pleistocene boundary marine extinction.     

Influence of attenuation on the behavior of refracted elastic waves at the interface between anisotropic media

During the ultrasonic non-destructive evaluation of complex materials, like multilayer or composite materials, the behavior of the ultrasonic waves at the interface of samples is strongly dependent upon the anisotropy as well as the attenuation characteristics of the propagation media. In the generally arbitrary case, the incident wave is assumed to be inhomogeneous. Therefore the application of the Snell-Descartes laws requires to consider the real as well as the imaginary parts of all the quantities encountered during the study. In that aim, we use a representation of the complex slowness curves so-called slowness interface curves which point out the evolution of the interaction of the waves at the interface with the inhomogeneity factors, i.e. the imaginary part of the slowness vectors. The continuous distortion of the curves with the inhomogeneity factor increasing is an interesting approach of these complicated phenomena.     

Use of a microelectromechanical mirror for adaptive optics in the human eye

Ophthalmic instrumentation equipped with adaptive optics offers the possibility of rapid and automated correction of the eye's optics for improving vision and for improving images of the retina. One factor that limits the widespread implementation of adaptive optics is the cost of the wave-front corrector, such as a deformable mirror. In addition, the large apertures of these elements require high pupil magnification, and hence the systems tend to be physically large. We present what are believed to be the first closed-loop results when a compact, low-cost, surface micromachined, microelectromechanical mirror is used in a vision adaptive-optics system. The correction performance of the mirror is shown to be comparable to that of a Xinetics mirror for a 4.6-mm pupil size. Furthermore, for a pupil diameter of 6.0-mm, the residual rms error is reduced from 0.36 to 0.12 microm and individual photoreceptors are resolved at a pupil eccentricity of 1 degrees from the fovea.     

Implications of $B \to \rho \gamma$ measurements in the standard model and supersymmetric theories

We study the implications of the recently improved upper limits on the branching ratios for the decays , expressed as . We work out the constraints that the current bound on implies on the parameters of the quark mixing matrix in the standard model (SM). Using the present profile of the unitarity triangle, we predict this ratio to lie in the range (at 95% C.L.), with the central value . We also work out the correlations involving , the isospin-violating ratio , and the direct CP-violating asymmetry in decays in the SM, in the minimal supersymmetric extension of the SM (MSSM), and in an extension of the MSSM involving an additional flavor-changing structure in transitions. Received: 19 August 2002 / Published online: 18 October 2002 RID="a" ID="a" e-mail: ali@mail.desy.de RID="b" ID="b" e-mail: lunghi@mail.desy.de