Determination of carbohydrates in juices by capillary electrophoresis, high-performance liquid chromatography, and matrix-assisted laser desorption/ionization-time of flight-mass spectrometry

The objective of this work was to develop a sample preparation procedure for determination of the carbohydrate profiles in commercial juice samples by three principally different analytical methods: capillary electrophoresis (CE) with indirect detection, high-performance liquid chromatography (HPLC), and matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). The preparation and purification of juice samples prior to analysis is described. The method using Carrez reagents was found to be an efficient preparation tool for all three methods. The addition of Carrez reagents to the samples for mass analysis improved the quality of the mass spectra of oligosaccharides. The amounts of glucose, fructose, and sucrose as major carbohydrates in fruit juices measured by CE using a simple instrument are in good agreement with the HPLC values and the data declared by the producers of the juices. The results from both methods are critically evaluated and their impact for studies of authenticity is discussed. The decrease of sucrose amount during the storage of samples was explained by acid hydrolysis of this disaccharide.     

The mechanism of the electrochemical oxidation of thiourea

Cyclic voltammetry and potentiostatic coulometry were used to study the electrochemical oxidation of thiourea in aqueous solutions of nitric acid, nitric acid—ammonium nitrate, and ammonium nitrate—ammonium hydroxide and in acetonitrile. These studies were carried out at glassy carbon and/or platinum working electrodes. In acetonitrile, the cyclic voltammograms show one oxidation peak at + 0.6 V and a reduction peak at —0.1 V. In aqueous solutions up to about pH 6, there is a second oxidation peak at 1.3 V which is irreversible and its height is sensitive to acidity. These experiments have confirmed that in acidic and neutral solutions the oxidation of thiourea proceeds via a slow 1-e transfer reaction producing a radical [(NH₂)₂—C—S]⁺. Further direct oxidation of this radical takes place only at higher potentials (ca. 1.2 V) and involves hydration and protontransfer equilibria. Otherwise, C,C'-dithiodiformamidinium ion is formed by a fast dimerization reaction. Coulometric and chronopotentiometric measurements have shown that in strong acid the second oxidation step involves one electron, while at lower acidities the further oxidation involving three (and possibly five) electrons proceeds in two (or three) steps of very similar potential.     

Decomposition of nitrogen and dinitrogen oxides on copper and copper(I) oxide in elemental analysis by reaction gas chromatography

The decomposition of NO and N₂O on Cu and Cu₂O packings was studied in view of the simultaneous determination of N and S in organic compounds by the Pregl-Dumas method in a system of reaction gas chromatography, and the mass balance of the reactions taking place was carried out. The amounts of NO and N₂O that are decomposed on the reduction packing at temperatures within 883 and 1263 °K are quoted. The reduction activity of both packings toward NO decreases with increasing temperature, while both the reduction and sorption activity of Cu₂O is markedly lower than that of the Cu one. No significant sorption of NO was observed at temperatures within 883 and 923 °K and no sorption of gaseous N₂ and N₂O occurred on either packing.     

Determination of salbutamol using on-line solid-phase extraction and sequential injection analysis. Comparison of chemiluminescence and fluorescence detection

Determination of salbutamol using sequential injection analysis (SIA) with chemiluminescence and fluorescence detection has been devised. The chemiluminescence signal was emitted during the oxidation of salbutamol by potassium permanganate in sulfuric acid medium. Sodium polyphosphate was used as chemiluminescence enhancer. The fluorescence signal (excitation wavelength 230 nm) was also measured in sulfuric acid medium. Both detection techniques were compared with respect to the application of the methods to the determination of salbutamol in biological materials. The sample pre-treatment takes place directly in the SIA system, when salbutamol is adsorbed on the solid-phase (Baker-carboxylic acid) microcolumn integrated into the system. Sulfuric acid serves both as the reagent and the eluent. The lab-made SIA system consisted of a 2.5-mL Cavro syringe pump, ten-port Vici Valco selection valve and Spectra-Physics FS 970 fluorescence detector, which was lab-modified for chemiluminescence detection. The system was controlled by a PC using originally compiled LabVIEW-supported software. Concentrations, volumes of reagents and flow rates were optimised by a simplex method. Salbutamol was determined in the linear range 0.05-10 microg mL(-1) (RSD 1.53%), with the detection limit (3 sigma) 0.03 microg mL(-1) and sample throughput of 42 samples per hour with chemiluminescence detection in standard solutions. The fluorescence detection enabled the determination of salbutamol in standard solutions in the linear range 0.5-100 microg mL(-1) (RSD 2.69%), with the detection limit 0.2 microg mL(-1) and sample throughput of 24 h(-1). The proposed methods were applied to the determination of salbutamol in human serum and urine. However, serum is a very complicated matrix and the SIA-SPE analysis did not provide satisfactory results. It was possible to determine salbutamol in human urine using this technique. Better recovery was achieved with fluorescence detection.     

Structural peculiarities, and electrical and optical properties of 70TeO2·30PbCl2 glasses doped with Pr, prepared in Pt or Au crucibles

The influence of crucibles (Au or Pt) on the structure, electrical, dielectric and optical properties of 70TeO₂·30PbCl₂ glasses doped with Pr³⁺ added as a metal, chloride, or oxide, in concentrations of 500–1500 wt-ppm, is reported. The dc conductivity of ‘pure’ glasses prepared in Au crucibles is two orders of magnitude higher than that of those prepared in Pt crucibles. Upon doping, the dc conductivity of glasses prepared in Pt and Au crucibles increases or decreases, respectively. The static relative permittivity is equal to 33 ± 2. In the range of 640–700 nm, six photoluminescence (PL) peaks were observed, at 641.5, 647.1, 652.4, 660.8, 662.9, and 664.5 nm. In the range of 200–1200 cm⁻¹, seven Raman scattering (RS) peaks were observed at 184, 217, 321, 468, 654, 735 cm⁻¹, and a small peak at 650 cm⁻¹. Both spectra were deconvoluted using symmetrical Gaussian functions. Relative intensities of PL and RS bands depend on the concentration and chemical form of Pr³⁺ and on the material of the crucible. However, positions of these bands are independent of these conditions.     

Asset-liability management for Czech pension funds using stochastic programming

It is possible to model a wide range of portfolio management problems using stochastic programming. This approach requires the generation of input scenarios and probabilities, which represent the evolution of the return on investment, the stream of liabilities and other random phenomena of the problem and respect the no-arbitrage properties. The quality of the recommended capital allocation depends on the quality of the input scenarios and a validation of results is necessary. Appropriate scenario generation techniques and output analysis methods are described in the context of defined contribution pension fund and applied to the specific model of a Czech pension fund. The numerical results indicate various components that influence the recommended investment decisions and the fund’s achievements. In particular, the initial balance sheet position of the pension fund is important for the optimal investment strategy because of the accounting rules embedded in the model and tracking of both the market and purchasing value of assets.     

Inverse cationic ITP for separation of methadone enantiomers with sulfated β‐cyclodextrin as chiral selector

Chiral ITP of the weak base methadone using inverse cationic configurations with H⁺ as leading component and multiple isomer sulfated β‐CD (S‐β‐CD) as leading electrolyte (LE) additive, has been studied utilizing dynamic computer simulation, a calculation model based on steady‐state values of the ITP zones, and capillary ITP. By varying the amount of acidic S‐β‐CD in the LE composed of 3‐morpholino‐2‐hydroxypropanesulfonic acid and the chiral selector, and employing glycylglycine as terminating electrolyte (TE), inverse cationic ITP provides systems in which either both enantiomers, only the enantiomer with weaker complexation, or none of the two enantiomers form cationic ITP zones. For the configuration studied, the data reveal that only S‐methadone migrates isotachophoretically when the S‐β‐CD concentration in the LE is between about 0.484 and 1.113 mM. Under these conditions, R‐methadone migrates zone electrophoretically in the TE. An S‐β‐CD concentration between about 0.070 and 0.484 mM results in both S‐ and R‐methadone forming ITP zones. With >1.113 mM and < about 0.050 mM of S‐β‐CD in the LE both enantiomers are migrating within the TE and LE, respectively. Chiral inverse cationic ITP with acidic S‐β‐CD in the LE is demonstrated to permit selective ITP trapping and concentration of the less interacting enantiomer of a weak base.     

Sequential injection extraction based on restricted access material for determination of furosemide in serum

Restricted access material (RAM) column containing 25 microm C18 alkyl-diol support was integrated into the sequential injection analysis (SIA) manifold and the SIA-RAM system was tested for direct determination of furosemide in serum. LiChrospher ADS column based on restricted access material is proposed to direct injection of biofluids. The integration of RAM material into SIA enabled creation of a comprehensive on-line sample clean-up technique combined with fluorescence quantitation of analyte. Centrifuged and diluted serum sample was aspirated into the system and loaded onto the column using acetonitrile-water (2:98), pH 2.7. The analyte was retained on the column while proteins contained in the sample were removed to the waste without precipitation and clogging the column. Interfering substances complicating the detection were washed out by acetonitrile-water (15:85), pH 2.7 in the next step. The extracted analyte was eluted by means of acetonitrile-water (25:75), pH 2.3 to the fluorescence detector (emission filter 385 nm). The whole procedure comprising sample pre-treatment, analyte detection and column reconditioning took 20 min. The recoveries of furosemide from serum lay between 101.4 and 103.4% for three concentrations of analyte.     

Zur Acetylierung von nichtreduzierenden Oligosacchariden

Ohne Zusammenfassung     

A note on deterministic equivalents to stochastic linear programming problems

Summary Generalized inverse matrices are used as a tool for a study of two-stage linear program under uncertainty. For a special choice of M which represents an extension of the so-called complete problem, a deterministic equivalent is given in the explicite form.