New method for the determination of four antiepileptic drugs in human plasma by high performance liquid chromatography

Summary The concurrent administration of several antiepileptic drugs for the treatment of seizure disorders has become common practice. Lamotrigine is a new antiepileptic given in combination with other antiepileptic drugs, but which is not routinely measured in clinical laboratories. An isocratic high-performance liquid chromatographic method is described for the simultaneous measuring lamotrigine, carbamazepine, phenobarbital and phenytoin within 10 minutes. The chromatographic system used an Hichrom Spherisorb CN column (20 cm×4 mm, i.d., 5 m particle size), a Bondapak CN precolumn, and a mobile phase consisting of methanol : acetonitrile : 5 mM sodium acetate (5:20:75: by volume, pH adjusted to 6.3 with acetic acid). BWA 725C was used as internal standard. The drugs were extracted from 200 l of plasma with ethyl acetate, acetonitrile and 5 mM sodium acetate. After evaporation of the organic layer and reconstitution in mobile phase, 25 l of extract was eluted with mobile phase at a flow rate of 1.2 ml/min. The eluted drugs were detected by their absorption at 205 nm and quantified from their peak heights. The method was found to be rapid, relatively simple to perform and sufficiently sensitive to determine each drug over its entire therapeutic range. Lower limits of detection varied from 50–100 ng/ml, absolute recoveries from 93–98%, and mean intra- and inter-assay CVs were <3.0%.     

Complexation-mediated crystallization. Crystallization of sodium acetate trihydrate needles from cyclohexane solution

The phenomenon of complexation-mediated crystallization is introduced and proposed as a new means for the preparation of novel forms of materials. Attempted crystallization of complexes of salts with crown ethers often results in the precipitation of the uncomplexed salt rather than the complex. In this study, a solution of the 15-crown-5 complex of sodium acetate in cyclohexane precipitated uncomplexed sodium acetate trihydrate as single crystals. The crystal morphology (long needles) of this crystalline sodium acetate stands in sharp contrast to the hexagonal plates known to form from aqueous solution. X-ray diffraction analysis revealed that sodium acetate as crystallized from cyclohexane solution adopted a crystal lattice identical to that in sodium acetate crystallized from aqueous solution. Possible origins of the change in crystal morphology are discussed.     

Slurry Sampling Electrothermal Atomic Absorption Spectrometric Determination of Sodium and Iron Impurities in Optical Crystals of Rubidium Titanyl Phosphate

A simple and rapid slurry sampling electrothermal atomic absorption spectrometric (ETAAS) method was developed for the determination of traces of sodium and iron in single crystals of rubidium titanyl phosphate (RTP). The finely ground crystal material was dispersed in 5mL of 2% (v/v) HNO₃, containing 0.005% (v/v) Triton-X-100. The fast furnace ETAAS analysis was performed using a pyrolytic platform coated with titanium carbide. No matrix interference was registered for either of the analytes in slurries containing 4 to 10mgmL^–1 of RTP, which permitted simple calibration against aqueous solutions. The precision was about 2% RSD. The results for sodium and iron content in RTP were in good agreement with those obtained by flame AAS after sample digestion.     

Catalytic Determination of Trace Formaldehyde with a Flow Injection System Using the Indicator Reaction between Crystal Violet and Bromate

A sensitive flow injection method is proposed for the determination of formaldehyde based on its catalytic action upon the redox reaction between crystal violet and potassium bromate in phosphoric acid medium. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of crystal violet injected at the maximum absorption wavelength of 600nm. A calibration graph from 0.018 to 1.400µgmL^–1 is obtained, and the detection limit is 0.007µgmL^–1 in a sample volume of 30µL. Up to 15 samples can be analyzed per hour with a relative standard deviation of 1.2 and 2.3%, respectively, for the determination of 1.0 and 0.1µgmL^–1 of formaldehyde. The method is free from most interference. This method has been applied to the determination of formaldehyde in air, decoration boards and paints, and the results compare well with those provided by iodimetry.     

Kinetic study of Pt-cytostatics reactions by HPLC

HPLC with DAD (diode array detector) was applied as rapid method for the analytical control of the purity and stability of carboplatin and oxocarboplatin as effective cytostatics of 2nd generation. The stability of carboplatin has been measured in some infusion media (sodium chloride, glucose, sodium citrate) and compared to the cisplatin (cytostatic of 1st generation) stability. In addition ligand-exchange reactions between cisplatin and carboplatin have been studied together with the influence of temperature, pH and the concentrations of reactants. A method was developed for the analysis of clinical samples using solid-phase extraction as a preseparation and preconcentration step. The detection limits were 5 g/ml serum for cisplatin, 0.16 g/ml for carboplatin and 0.23 g/ml for oxo-carboplatin.Dedicated to Professor J. F. K. Huber on the occasion of his 65th birthday     

Indirect complexometric determination of palladium(II) using sodium nitrite as a selective masking reagent

A selective complexometric method is described for the determination of palladium, sodium nitrite being used as masking reagent. Palladium(II) in a given sample solution is initially cornplexed with an excess of EDTA and the surplus EDTA is titrated with zinc sulfate solution at pH 4.5–5.5 (acetic acid-sodium acetate buffer), using xylenol orange as indicator. An excess of sodium nitrite is then added, the mixture is shaken well and the EDTA released from the Pd-EDTA complex is titrated with a standard zinc sulfate solution. Results are obtained for 2.5–27.5 mg of Pd with relative errors 0.5% and standard deviations 0.05 mg. The interferences of various ions are studied. The method is applied for the determination of palladium(II) in alloys and complexes.     

Spectrofluorimetric determination of guanethidine sulphate,guanfacine hydrochloride,guanoclor sulphate and guanoxan sulphate in tablets and biological fluids,using benzoin

A sensitive and rapid Spectrofluorimetric method for the determination of guanethidine sulphate, guanfacine hydrochloride, guanoclor sulphate and guanoxan sulphate in tablets and spiked human serum and urine samples is described. The method is based on the reaction of monosubstituted guanidino compounds in an aqueous potassium hydroxide solution with benzoin, in the presence of -mercaptoethanol and sodium sulphite. Highly fluorescent derivatives were obtained, with excitation and emission maximum wavelengths around 325 and 430 nm, respectively. In optimal reaction conditions, the linearity ranges were 0.04–0.28 g/ml, with relative standard deviations less than 2%. The method has been successfully applied to the determination of these drugs in tablets. The results are highly correlated with the B.P. method. Chloroform (or for guanoxan dichloromethane) was used to extract the drugs from serum and urine at basic pH, followed by the proposed fluorimetric method. The limit of detection is 0.02 g/ml for the selected drugs.     

Gas-liquid chromatographic resolution of free dichlorophenol isomers on new stationary liquid phases

Summary It is difficult to separate all the dichlorophenol isomers as free phenols by gas-liquid chromatography. However they were effectively separated on 4,4-dimethoxyazoxybenzene (liquid crystal), and all the isomers were separated appreciably well on sodium 1-naphthalenesulfonate, 2-naphthalenesulfonate and dodecylbenzenesulfonate.     

Transport processes in mixed conducting oxides: combining time domain experiments and frequency domain analysis

The conductivity relaxation (CR) method is often used for measuring the surface transfer rate, K_tr, and the bulk diffusion coefficient, for oxygen transport in mixed conducting oxides (MIECs). The time domain analysis of the obtained CR response is rather complex and is based on ideal behaviour for the diffusion process. It is quite favourable to perform the data analysis in the frequency domain, where non-ideal responses are easily recognised. Besides, frequency domain analysis (impedance spectroscopy) can yield reliable parameter estimates. Using a discrete Fourier-transform procedure, the time domain responses can be transformed to a frequency domain impedance-type expression. This approach can be applied to any system for which a driving force and a resulting flux can be defined.Presented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10–12 April 2003     

Complexation properties and characterization of four conformers of a [2.1.2.1]metacyclophane

Cone, partial cone, 1,2-alternate, and 1,4-alternate conformers of tetrakis[(ethoxycarbonyl)-methoxy] [2.1.2.1]metacyclophane (MCP,2) were isolated and characterized by¹H-NMR and an X-ray crystal structure analysis of the 1,4-alternate conformer. Of the four conformers, only the cone conformer2d forms a complex with alkali metals. The stability constants of2d with alkali metal ions were determined by the direct¹H-NMR method and UV spectra, and the order observed as potassium cesium, sodium ions.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

Synthesis and Heterocyclization of 3-Arylaminothiocrotonanilides

Reactions of acetylthioacetanilide with arylamines in acetic acid in the presence of sodium acetate give 3-arylaminothiocrotonanilides in good yields. When treated with -bromoacetophenone in acetone, these products are converted to substituted 4-hydroxy-²-thiazolinium bromides, one of which was dehydrated to obtain the corresponding thiazolium bromide. The structure of the heterocyclization products was confirmed by single crystal X-ray diffraction and NMR study of 2-acetonylidene-3,4-diphenyl-2,3-dihydrothiazole formed by dehydration of the corresponding ²-thiazolinium salt with simultaneous hydrolysis.     

Interaction of 1-(2-tetrahydrofuryl)-5-fluorouracil with sodium poly-α,L-glutamate

Summary The interaction of an anticancer drug, 1-(2-tetrahydrofuryl)-5-fluorouracil with sodium poly-,L-glutamate in aqueous solution was studied with a spectral method and viscosity measurement. From the binding data, the molar change in enthalpy, entropy and the number of binding sites on polymer were calculated. The standard affinity of 1-(2-tetrahydrofuryl)-5-fluorouracil is about –10 kcal/ol with sodium poly-,L-glutamate. The affinity is also very high.With 6 figures and 2 tables     

Piezoelectric enzyme sensor with improved temperature characteristics for determining urea in urine

Based on the conductivity change produced by the urea/urease reaction, a piezoelectric enzyme sensor is applied to the detection of urea in urine. The influence of the variation in solution temperature on frequency measurement is greatly reduced by using a buffer giving solution conditions with a near-zero frequency temperature coefficient for the sensor. The sum of the frequency shifts over the reaction time was used to increase the sensitivity of the determination. The linear range of the method is 1–30 g/ml for urea, with RSDs of 1–2.6%. The detection limit is 0.01 g/ml.     

Substoichiometric radiochemical determination of thallium with sodium isopropyl xanthate

A rapid radiochemical method for the determination of thallium(III) has been developed based on the substoichiometric extraction of its 13 complex with sodium isopropyl xanthate into chloroform from pH 9 ammonia buffer. The effect of foreign ions on the extraction was also studied. 10 g amounts of thallium were determined with an average error of 1.9%. The method has been successfully applied for the determination of thallium content present in sphalarite ores collected from Jawar Mines, Rajasthan (India).     

Bestimmung von Calciumgehalten im ppm-Bereich in Natriummetall mit Hilfe der R?ntgenfluorescenzanalyse

Zusammenfassung Eine Methode zur Bestimmung von Calcium in Natriummetall wird beschrieben. Das Natriummetall wird mit Methanol, H₂O und H₂SO₄ zu Na₂SO₄ umgesetzt, dieses in einem Platin-Tiegel zu Scheiben geschmolzen und diese direkt mit dem Röntgenfluorescenzgerät gemessen (Cr-Röhre, 55 kV, 36 mA; Analysatorkristall LiF; Ca-K-Linie, 113,01°). Die Nachweisgrenze dieser Methode liegt bei 4 ppm und gestattet daher noch eine sichere Aussage über die bei Na-Metall Reaktorqualität geforderte Spezifikation < 10 ppm Ca.

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Determination of ppm amounts of calcium in sodium metal by X-ray fluorescence analysis

The metal is converted to Na₂SO₄ by treatment with methanol, water and sulphuric acid. The salt is fused in a platinium crucible to form disks which can be directly measured in the X-Ray fluorescence apparatus (Cr tube, 55 kV, 36 mA; analyzing crystal LiF; Ca-K-line, 113.01°). The limit of detection of the method is as low as 4 ppm and thus permits reliable statements with regard to the specification < 10 ppm Ca required for reactor quality sodium metal.

     

Effects of Sodium Salts Organic Acids Modification on the Microstructure and Dispersion Behavior of Palygorskite Nano-Powder via High-Pressure Homogenization Process

High-pressure homogenization could disaggregate the crystal bundles of palygorskite and favor the adsorption of electrolyte ions onto its surface through the produced cavitation, shear, and turbulence forces, and has evident influences on the micromorphologies and properties of clay. In this work, a series of palygorskite samples modified with sodium citrate, sodium benzoate, sodium lactate, sodium acetate, and sodium propionate were obtained under the condition of high-pressure homogenization. The effects of type and concentration of sodium salts organic acids on the microstructure, morphology, surface charge, and physicochemical property of palygorskite were studied through x-ray diffraction (XRD), N₂ adsorption–desorption isotherm, field emission scanning electron microscopy, zeta potential, rotational viscosity, and rheological measurements. XRD results confirmed that the crystal structure of homogenized palygorskite was not changed after introduction of sodium salts organic acids, but the aggregates were effectively disaggregated. Modification of palygorskite with sodium citrate made the surface more negatively charged, and the samples exhibited higher specific surface area and rheological properties. This work provided a method to improve the rheological properties of palygorskite suspension through dispersion of clay in sodium citrate solution followed by homogenization at 30 MPa.      

Room temperature synthesis and solid-state structure of Ni2P2O6·12H2O

The synthesis and crystal structure of Ni₂P₂O₆·12H₂O are reported. The compound was synthesized from aqueous solutions of nickel chloride and sodium hypodiphosphate at room temperature. The space group is orthorhombic, Pnnm. Unit cell dimensions are , , and , Z=4. The product is unstable with respect to dehydration above room temperature.     

Flow Injection Chemiluminescence Determination of Hemin Using the Rhodamine B–H2O2–NaOH System

A flow injection chemiluminescence method has been developed and applied to the determination of hemin in tablets and animal blood. The proposed method is based on the luminescent properties of the Rhodamine B–H₂O₂–NaOH system and the addition of sodium dodecyl sulfonate (SDS) as emission-sensitizer. Hemin was determined over the concentration range of 8.6×10^–10–8.6×10^–7M with a detection limit of 8.6×10^–11M (3). The relative standard deviation (RSD) for seven independent detections of 1.72×10^–8M hemin was 3.0%. The proposed method was successfully applied to the analysis of hemin in pharmaceutical preparations and animal blood with a recovery of 96–108%. A possible CL mechanism of the present system was discussed, and free radicals were suggested to be involved in this reaction.     

A new chromatographic method for the separation of food dye mixtures on thin MgO layers

Summary A new effective TLC method has been developed for the separation of the five main watersoluble food dyes such as indige carmin, cochineal red, acid amaranth I, orange yellow S and tartrazine G. The chromatograms are developed by the ascending technique on thin MgO layers applied onto glass plates, previously activated at 130°C. A 82 mixture of 15% sodium citrate and methanol is used as the developing phase. This composition was selected on the basis of Snyder's theory and the polarity index which for this mixture is 8.3. The proposed method permits the full separation of the dye mixture from a 0.3l sample solution with concentrations of 1×10^–6 mole/liter.     

The reconstruction of atomic co-ordinates from a protein stereo ribbon diagram when additional information for sufficient sidechain positions is available

We describe the application of a method for the reconstruction of three-dimensional atomic co-ordinates from a stereo ribbon diagram of a protein when additional information for some of the sidechain positions is available. The method has applications in cases where the 3D co-ordinates have not been made available by any means other than the original publication and are of interest as models for molecular replacement, homology modelling etc. The approach is, on the one hand, more general than other methods which are based on stereo figures which present specific atomic positions, but on the other hand relies on input from a specialist. Its exact implementation will depend on the figure of interest. We have applied the method to the case of the -d-galactose-binding lectin jacalin with a resultant RMS deviation, compared to the crystal structure, of 1.5 Å for the 133 C positions of the -chain and 2.6 Å for the less regular -chain. The success of the method depends on the secondary structure of the protein under consideration and the orientation of the stereo diagram itself but can be expected to reproduce the mainchain co-ordinates more accurately than the sidechains. Some ways in which the method may be generalised to other cases are discussed.