On-line sample cleanup and enrichment chromatographic technique for the determination of ambroxol in human serum

A sensitive and efficient on-line clean up and pre-concentration method has been developed using column-switching technique and protein-coated μ-Bondapak CN silica pre-column for quantification of ambroxol (AM) in human serum. The method is performed by direct injection of serum sample onto a protein-coated μ-Bondapak CN silica pre-column, where AM is pre-concentrated and retained, while proteins and very polar constituents are washed to waste using a phosphate buffer saline (pH 7.4). The retained analyte on the pre-column is directed onto a C(18) analytical column for separation, with a mobile phase consisting of a mixture of methanol and distilled deionized water (containing 1% triethylamine adjusted to pH 3.5 with ortho-phosphoric acid) in the ratio of 50:50 (v/v). Detection is performed at 254 nm. The calibration curve is linear over the concentration range of 12-120 ng/mL (r(2) = 0.9995). The recovery, selectivity, linearity, precision, and accuracy of the method are convenient for pharmacokinetic studies or routine assays.     

Determination of memantine in rat plasma by HPLC-fluorescence method and its application to study of the pharmacokinetic interaction between memantine and methazolamide

A sensitive high-performance liquid chromatographic method with fluorescence detection was developed to determine memantine (MT) in rat plasma. The method consists of pre-column labeling of MT with 4-(4,5-diphenyl-1H-imidazol-2-yl)benzoyl chloride (DIB-Cl) and a clean-up step with solid-phase extraction. A good separation of DIB-MT was achieved within 12 min on an octadecylsilica (ODS) column (150 × 4.6 mm i.d.; 5 μm) with a mobile phase of acetonitrile-water (70:30, v/v). The calibration curve prepared with fluoxetine as an internal standard showed good linearity in the range of 10-400 ng/mL (r = .999). The limits of detection and quantitation at signal-to-noise ratios of 3 and 10 were 2.0 and 6.6 ng/mL, respectively. The method was shown to be reliable with precisions of <5% for intra-day and <9% for inter-day as relative standard deviation. The fluorescence property and reaction yield of authentic DIB-MT were also examined. The proposed method was successfully applied to study the pharmacokinetic interaction between MT and methazolamide.     

Steric and Inductive Effects on Ionic Association in Aqueous Solutions Using an ion Selective Electrode Technique. II. Magnesium Salts

The stoichiometric association constants, K, the thermodynamic association constants, K_A, and the thermodynamic parameters ΔS°, ΔH°, ΔG° for the association between Mg(II) ion with o-, m and p-toluates,o-,m, and p-chlorobenzoates, and o-, m- and p-bromobenzoates have been determined at 15°C, 25°C, 35°C and 45°C in aqueous media. Ion selective electrodes were used to measure the Mg^{2 +} activities. The trends in the association behavior of Mg(II) salts of aromatic acids connot be explained on the basis of steric effects but can be explained according to the trend of the pKa of the parent organic acids, and the Hammett function, σ, of the salts themselves relative to the corresponding benzoate salt.     

The polarographic behaviour of ketoprofen and assay of its capsules using spectrophotometric and voltammetric methods

The quantitative determination of ketoprofen using spectrophotometric and voltammetric methods are described. The spectrophotometric procedure depends upon the reaction of ketoprofen with N-bromosuccinimide (NBS). The residual reagent is then determined by formation of violet colour with 2,2-diphenyl-l-picryl hydrazine (DPPH(2)). The consumed NBS would correspond to ketoprofen. Beer's law is valid over the concentration range 5-80 mug/ml of the drug. Direct current (DC) polarography allows to study the reduction behaviour of ketoprofen at the dropping mercury electrode (DME) using different supporting electrolytes at different pH values. Direct current stripping voltammetry (DCSV) was used for the quantitative measurements of the drug. The calibration graph of peak current vs concentration was linear from 0.254 x 10(-2) to 0.254 mug/ml. In model solutions as little as 5.08 x 10(-4) ng/ml ketoprofen can be detected by DCSV. Both methods were applied successfully for the determination of ketoprofen either in pure or dosage forms.     

Synthesis and spectroscopic studies of new binuclear transition metal complexes of Schiff bases derived from 4,6-diacetylresorcinol

Two new series of copper(II), nickel(II), cobalt(II), zinc(II), iron(III), chromium(III), vanadyl(IV) and uranyl(VI) complexes with two bifunctional tridentate Schiff base, H₄L¹ and H₂L² ligands have been prepared. The Schiff base, H₄L¹ and H₂L², ligands were synthesized by the condensation of 4,6-diacetylresorcinol with o-aminophenol or o-phenylenediamine. The ligands are either di- or tetra-basic with two symmetrical sets of either OON or NNO tridentate chelating sites. The ligands and their metal complexes have been characterized by elemental analysis, ¹H-n.m.r., FT-IR, mass, electronic, esr spectra and thermal gravimetric analysis and magnetic susceptibility. With the exception of Co^II ion with H₂L² which afforded a trinuclear complex, a variety of binuclear complexes for the rest of the metal complexes were obtained with the ligands in its di- or tetra-deprotonated forms. The bonding sites are the azomethine and amino nitrogen atoms, and phenolic oxygen atoms. The metal complexes exhibit different geometrical arrangements such as square planar, tetrahedral, square pyramid and octahedral arrangement.     

Determination of phenyltoloxamine salicylamide, caffeine, paracetamol, codeine and phenacetin by HPLC

A reversed-phase high-performance liquid chromatographic method for the determination of six common analgesics (phenyltoloxamine dihydrogen citrate, salicylamide, caffeine, paracetamol, codeine phosphate and phenacetin) is presented. The method is specific for detection and determination of each of these compounds in a complex mixture, without pretreatment. A 10-mum C(18) silica gel stationary phase is used with a methanol-acetonitrile-water-tetrahydrofuran mixture (20:20:55:5 v/v) and spectrophotometric detection at 254 nm. All six components are eluted within 7 min. The method has given good results for three commercial products containing two, three and five active ingredients respectively. Phenacetin, a common analgesic which might be found in other formulations, is used as an internal standard.     

Validated Optimized Method for Simultaneous Analysis of Active Silymarin Components and Dimethyl-4,4′-dimethoxy-5,6,5′,6′-dimethylene Dioxybiphenyl-2,2′-dicarboxylate in a Pharmaceutical Preparation by Use of a Monolithic Silica C18 Column

A simple, rapid, and sensitive isocratic reversed-phase LC method using a monolithic column has been developed and validated for simultaneous analysis of the active components of silymarin [taxifolin, silydianin, silychristin, diastereomers of silybin (silybin A and B), and diastereomers of isosilybin (isosilybin A and B)] and dimethyl-4,4′-dimethoxy-5,6,5′,6′-dimethylene dioxybiphenyl-2,2′-dicarboxylate in a commercial formulation. The mobile phase was a 45:55 (v/v) mixture of methanol and 5 mM NaH₂PO₄ (adjusted to pH 2.75 with phosphoric acid) at a flow rate of 1.5 mL min^?1. UV detection was performed at 288 nm and quantification was based on peak area. The method was validated for linearity, accuracy, precision, selectivity, and robustness.     

Liquid chromatography determination of citalopram enantiomers using beta-cyclodextrin as a chiral mobile phase additive

A reliable and specific method for the determination of citalopram enantiomers was developed and validated. Chromatographic resolution of citalopram enantiomers was made on a Shim-pack (5 microm particle size) cyanopropyl column with beta-cyclodextrin (beta-CD) as an effective chiral mobile phase additive. The composition of the mobile phase was (90 + 10, v/v) aqueous 0.1% triethylammonium acetate buffer, pH 4.0 (adjusted with acetic acid), and acetonitrile, containing 12 mM beta-CD. The flow rate was 0.8 mL/min with ultraviolet detection at 240 nm. The effects of the mobile phase composition, concentration of beta-CD, and pH of the triethylammonium acetate buffer on peak shape and resolution of the enantiomers were investigated. The calibration graphs were linear (r = 0.9999, n = 8) in the range of 1-40 microg/mL for S(+) citalopram and R-(-) citalopram. The limit of detection values were 5.51 x 10(-3) and 4.35 x 10(-3) pg/mL, while the limit of quantification values were found to be 1.84 x 10(-2) and 1.45 x 10(-2) microg/mL for S-(+) citalopram and R-(-) citalopram, respectively.     

CHARACTERIZATION OF NANOSTRUCTURES:TOOLS AND CHALLENGES

Apart from long-known and applied nanostructures like carbon black for tyres or pigments for coatings nanotechnology has created highly sophisticated structures used for nano/molecular electronics,diagnostics,drug delivery, UV-absorbers etc.Often the main question to be solved analytically is the local determination of tiny amounts of chemicals resulting in an ever increasing need for highly sensitive as well as locally resolved techniques.Applications of techniques like mass spectroscopy,transmission el...