Development and validation of a fast isocratic liquid chromatography method for the simultaneous determination of norfloxacin,lomefloxacin and ciprofloxacin in human plasma

A simple and fast liquid chromatographic method coupled with fluorescence detection (LC‐FD) is reported, for the first time, for the simultaneous quantification of norfloxacin (NOR), ciprofloxacin (CIP) and lomefloxacin (LOM) in human plasma, using levofloxacin as internal standard (IS). Sample preparation consists of a single‐step precipitation of plasma proteins followed by vortex‐mixing and centrifugation. Chromatographic separation was achieved within 7 min on a reversed‐phase C₁₈ column with a mobile phase consisting of 0.1% aqueous formic acid (pH = 3.0, triethylamine)–methanol (82:18, v/v) pumped isocratically at 1.2 mL/min. The detector was set at excitation/emission wavelengths of 278/450 nm. Calibration curves were linear (r² ≥ 0.994) in the range of 0.02–5.0 µg/mL, and the limit of quantification was established at 0.02 µg/mL for all analytes (NOR, CIP and LOM). The overall precision did not exceed 8.19% and accuracy was within ±10.91%. NOR, CIP and LOM were extracted from human plasma with an overall mean recovery ranged from 90.1 to 111.5%. No interferences were observed at the retention times of the analytes and IS. This novel LC‐FD method enables the reliable determination of NOR, CIP and LOM in a single chromatographic run, which may be suitable to support human pharmacokinetic‐based studies with those antimicrobial agents. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and electrical properties of double borates Ba<Subscript>3</Subscript>R(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>, R = Ho,Yb, Sc

Polycrystalline samples of double barium borates of the composition Ba₃R(BO₃)₃, R = Ho, Yb, Sc, were synthesized by the method of solid-phase reactions. The temperature dependence of the electrical conductivity of the compounds obtained was studied at 200–500°C.     

Functionalized carbon dots as sensors for gold nanoparticles in spiked samples: Formation of nanohybrids

This paper reports the synthesis, passivation and functionalization of luminescent carbon dots (CDs) possessing surface thiol ending groups. A simple procedure involving amidation of passivated carbon dots (p-CDs) with cysteamine boosts their photoluminescent properties and enables their use as easily controlled fluorescent nanosensors for determining citrate–gold nanoparticles (AuNPs). The mechanism behind the quenching phenomenon was established from fluorescence measurements at high temperatures and lifetime tests, and found to involve static quenching leading to the formation of CD–AuNP nanohybrids. A method for determining AuNPs in complex matrices was developed and validated by application to spiked drinking water and mussel tissues. The limits of detection and quantitation for AuNPs thus obtained were 0.20 and 0.66 nmol L^–1, respectively.     

Comparative properties of Amazonian oils obtained by different extraction methods

Pequi (Caryocar brasiliense Camb.), baba?u (Orbignya phalerata Mart.), buriti (Mauritia flexuosa), and passion fruit (Passiflora edulis) oils were studied to determine their antibacterial, antioxidant and cytotoxic activities, as well as their total phenol and carotenoid contents. The fatty acid contents were determined by GC-MS. The three types of passion fruit oils studied were refined, cold pressed or extracted from seeds in a Soxhlet apparatus. The oils thus obtained showed differences in antioxidant activity and carotenoid content, but were similar in regard to total phenols. Buriti and pequi had the highest carotenoid contents, while refined and cold pressed passion fruit oil displayed the highest antioxidant activity. Pequi oil was the only oil to display antibacterial and cytotoxic activity.     

Identification and characterization of impurities of tetracosactide by capillary electrophoresis and liquid chromatography coupled to time-of-flight mass spectrometry

Tetracosactide is a synthetic peptide analogue of the human adrenocorticotropic hormone that stimulates the production of cortisol in the adrenal cortex. The medical use of the compound is primarily the diagnosis of the adrenal cortex function. In order to characterize impurities of the drug, tetracosactide samples were analysed by both liquid chromatography and capillary electrophoresis coupled to a quadrupole time-of-flight mass spectrometer. The identification of the impurities was carried out based on accurate mass determination and fragment ion spectra. The presence of several peptides of lower and higher masses than tetracosactide could be shown, including N- and C-terminally truncated peptides as well as peptides which still contained protecting groups or additional amino acids. Furthermore, a semi-quantitative estimation of the relative amounts of the impurities in different samples as well as a commercial preparation revealed that the number and the type of the impurities varied between the samples. Comparing the selectivity of liquid chromatography and capillary electrophoresis regarding the separation of tetracosactide impurities, it can be stated that capillary electrophoresis showed a higher suitability for the separation of tetracosactide fragments (smaller peptides) while the larger peptides, i.e. those wearing protecting groups, were separated more efficiently by liquid chromatography.     

The Influence of Nd and Sm on the Structure and Properties of Sol-Gel-Derived TiO2 Powders

TiO₂ nanopowders modified by Nd and Sm were prepared using the sol-gel technique. It was found by XRD analysis that the samples containing Sm are amorphous up to 300 °C, while those with Nd preserve a mixed organic-inorganic amorphous structure at higher temperatures (400 °C). The TiO₂ (rutile) was not detected up to 700 °C in the presence of both modified oxides. TiO₂ (anatase) crystals found at about 400 °C in the Sm-modified sample exhibited an average crystallite size of about 25–30 nm, while doping with Nd resulted in particles of a lower size—5–10 nm. It was established by DTA that organic decomposition is accompanied by significant weight loss occurring in the temperature range 240–350 °C. Photocatalytic tests showed that the samples heated at 500 °C possess photocatalytic activity under UV irradiation toward Malachite green organic dye. Selected compositions exhibited good antimicrobial activity against E. coli K12 and B. subtilis.     

Synthesis of N-(2-Hydroxyalkyl)trimethylsilylpropynamides

A number of previously unknown N-(2-hydroxyethyl)trimethylsilylpropynamides were synthesized by reactions of 2-aminoethyl trimethylsilyl ethers with trimethylsilylpropynoyl chloride. 2-Hydroxyethylamine reacts with trimethylsilylpropynoyl chloride at both nitrogen and oxygen atoms to afford 2-(3-trimethylsilylpropynoylamino)ethyl trimethylsilylpropynoate.     

Initial-layer theory and model equations of Volterra type

^** Email: amb16{at}nyu.edu It is demonstrated here that there exist initial layers to singularlyperturbed Volterra equations whose thicknesses are not of theorder of magnitude of O(), 0. It is also shown that the initial-layertheory is extremely useful because it allows one to constructthe approximate solution to an equation, which is almost identicalto the exact solution.