Effect of method of solution on observed molecular weight distribution of barley starch and starch derivatives in size exclusion chromatography

Summary Samples of native barley starch and six starch derivatives were suspended (0.1% sample concentration) in four different solvents: the eluent (pH 11 buffer), dimethylsulfoxide, 0.1 M NaOH or 0.5 M NaOH and kept in a boilling water bath for 5 to 60 minutes or shaken for 60 minutes. The average molecular weight values , and the polydispersity value were determined with a TSK PW-type column using narrow standard calibration. Only a small part of the samples dissolved in the eluent. The dissolution of sample in dimethylsulfoxide was dependent on sample type. Of the NaOH solutions, 0.5 M NaOH was the only one that dissolved all the samples. Therefore, 0.5 M NaOH appears to be the solvent of choice for starch molecules.     

Degradative analysis of aquatic fulvic acid: CuO oxidation versus pyrolysis after tetramethylammonium hydroxide treatments in air and helium atmospheres

The structural composition of Nordic aquatic reference fulvic acid was investigated using chemical and thermal degradation methods: alkaline CuO oxidation and analytical pyrolysis after tetramethylammonium hydroxide (TMAH) pretreatment. Off-line procedures of the TMAH treatments were carried out under both air and helium atmospheres, with the aim of clarifying the effect of oxygen. Irrespective of the fact that the chemical and thermal degradation methods gave qualitatively quite similar basic products (mainly phenols and phenolic acids together with aromatic and aliphatic carboxylic acids), they also revealed their unique selectivity and efficiency for releasing different kinds of structural constituents. The results verify the formation of additional carboxyl functionality in the CuO oxidation. However, some similar oxidative reactions also appeared to take place during the pretreatment procedures of strongly basic TMAH, especially under an air atmosphere. The use of inert and protective atmosphere during the TMAH pretreatment is therefore recommended for producing more relevant structural information about the complex composition of humic substances.     

Determination of biogenic amines in wine by multidimensional liquid chromatography with online derivatisation

An online multidimensional liquid chromatographic system was developed for online clean-up, derivatisation and separation of biogenic amines in wines. The system consists of a cation-exchange precolumn, a derivatisation coil and an analytical column, and a column-switching valve. The entire system can be easily automated. The method proved to be quantitative and sensitive. Limits of detection were below 0.05 mg l(-1) for all amines and linearity was preserved over the tested range (0.05-15 mg l(-1)). The method was applied to the analysis of red wines of different origin.     

Micellar electrokinetic capillary chromatography method for direct determination of glucuronides of entacapone and its (Z)-isomer in human urine

This paper describes the validation of a micellar electrokinetic capillary chromatography method for the direct determination of the 3-O-glucuronides of entacapone and its (Z)-isomer, the main urinary metabolites of entacapone in humans. Entacapone is a novel drug which, as a potent inhibitor of catechol-O-methyltransferase (COMT), is used as an adjunct in the standard therapy of Parkinson's disease. The 3-O-glucuronide of another COMT inhibitor, nitecapone, was used as internal standard (I.S.). The validation experiments were performed by using spiked urine samples that were extracted with Sep-Pak C18 cartridges before analysis. Determinations were carried out in a buffer of pH 7.0 containing 25 mM of phosphate, 50 mM of borate and 20 mM of sodium dodecyl sulfate, and by applying 15 kV over a 67 cm (60 cm to the detector) x 75 microns fused-silica capillary. UV detection was at 335 nm. The validity of the method was assessed by investigating the identity of the analytes, selectivity, limit of quantitation, linearity, within-day precision, extraction recovery, between-day precision and accuracy, electroosmotic flow stability and analyte stability. The method proved to be reproducible, sufficiently selective and accurate. Extraction recoveries of the analytes were > 94%. The limit of quantitation (LOQ) was 2 micrograms/ml and the assay was linear in the range 2-150 micrograms/ml with correlation coefficients better than 0.999 for both glucuronides. The repeatability of the method, expressed as the ratio of corrected peak area of the analytes to that of I.S., gave RSD values of < 5% even at the LOQ. Between-day precision (RSD) was < 7.5% for both glucuronides at 7.5 micrograms/ml. Determination of the glucuronide concentrations in urine samples of 34 patients treated with entacapone either orally (200 mg) or intravenously (25 mg) showed the method to be suitable for monitoring the concentrations of the glucuronide of entacapone after both oral and intravenous administration and those of the glucuronide of its (Z)-isomer after oral administration. The limited long term stability of the system requires, however, frequent recalibration in applications involving long sample series.     

Migration behaviour and separation of tramadol metabolites and diastereomeric separation of tramadol glucuronides by capillary electrophoresis

Capillary electrophoresis with UV detection was used to separate tramadol (TR), a centrally acting analgesic, and its five phase I (M1, M2, M3, M4, M5) and three phase II metabolites (glucuronides of M1, M4 and M5). Several factors were evaluated in optimisation of the separation: pH and composition of the background electrolyte and the influence of a micellar modifier, sodium dodecyl sulfate. Baseline separation of TR and all the analytes was obtained with use of 65 mM tetraborate electrolyte solution at pH 10.65. The lowest concentrations of the analytes that could be detected were below 1 microM for the O-methylated, below 2 microM for the phenolic and ca. 7 microM for the glucuronide metabolites. The suitability of the method for screening of real samples was tested with an authentic urine sample collected after a single oral dose (50 mg) of TR. After purification and five-fold concentration of the sample (solid-phase extraction with Oasis MCX cartridges), the parent drug TR and its metabolites M1, M1G, M5 and M5G were easily detected, in comparison with standards, in an interference-free area of the electropherogram. Diastereomeric separation of TR glucuronides in in vitro samples was achieved with 10 mM ammonium acetate-100 mM formic acid electrolyte solution at pH 2.75 and with basic micellar 25 mM tetraborate-70 mM SDS electrolyte solution at pH 10.45. Both separations showed that glucuronidation in vitro produces glucuronide diastereomers in different amounts. The authentic TR urine sample was also analysed by micellar method, but unambiguous identification of the glucuronide diastereomers was not achieved owing to many interferences.     

Route to broadband blue-light generation in microstructured fibers

We explore theoretically the possibility of generating broadband blue light by copropagating a short soliton pump pulse and a broader signal pulse in a microstructured fiber with a zero-dispersion wavelength located between the center wavelength of the pump and the signal pulses. We show that the unique properties of microstructured fibers should allow for broadening of the signal pulse's spectrum by as much as a factor of 50 through the conjugate action of cross-phase modulation and a soliton self-frequency shift. The physical mechanism that leads to this large spectral broadening is analyzed by use of an extended nonlinear Schr?dinger equation.     

Generalized entropy in expanded semigroups and in algebras with neutral element

The complex product of (non-empty) subalgebras of a given algebra from a variety \(\mathcal{V}\) is again a subalgebra if and only if the variety \(\mathcal{V}\) has the so-called generalized entropic property. This paper is devoted to algebras with a neutral element or with a semigroup operation. We investigate relationships between the generalized entropic property and the commutativity of the fundamental operations of the algebra. In particular, we characterize the algebras with a neutral element that have the generalized entropic property. Furthermore, we show that, similarly as for n-monoids and n-groups, for inverse semigroups, the generalized entropic property is equivalent to commutativity.     

Theoretical investigation of photoelectron spectra and magnetically induced current densities in ring-shaped transition-metal oxides

The molecular structures of cyclic group 6 transition-metal (M = Cr, Mo, W, Sg) oxides (M ₃O ₉ ^0/1?/2? ) species have been optimized at density functional theory (DFT) levels. The photoelectron spectra (PES) of M ₃O ₉ ^? (M = Cr, Mo, W) were calculated at the time-dependent DFT and approximate coupled-cluster singles doubles (CC2) levels and compared with experimental results. The CC2 calculations did not yield any reliable PES, whereas the molecular structures can be identified by comparing PES obtained at the DFT level with experiment. Magnetically induced current densities were calculated at the DFT level using the gauge-including magnetically induced current (gimic) approach. The current strengths and current pathways of the neutral M₃O₉ and the dianionic M₃O ₉ ^2? (M = Cr, Mo) oxides were investigated and analyzed with respect to a previous prediction of d-orbital aromaticity for Mo₃O₉ anions. Current-density calculations provide ring-current strengths that are used to assess the degree of aromaticity. Comparison of current-density calculations and calculations of nucleus-independent chemical shifts (NICS) shows that NICS calculations are not a reliable tool for determining the degree of aromaticity of the metal oxides.     

The gauge including magnetically induced current method

An overview of applications of the recently developed gauge including magnetically induced current method (GIMIC) is presented. The GIMIC method is used to obtain magnetically induced current densities in molecules. It provides detailed information about electron delocalization, aromatic character, and current pathways in molecules. The method has been employed in aromaticity studies on hydrocarbons, complex multi-ring organic nanorings, M?bius twisted molecules, inorganic and all-metal molecular rings and open-shell species. Recent studies on hydrogen-bonded molecules indicate that GIMIC can also be used to estimate hydrogen-bond strengths without fragmentation of the system. Preliminary results are presented on the applicability of GIMIC for investigating current transport in molecules attached to clusters simulating molecular conductivity measurements. Advantages and limitations of the GIMIC method are reviewed and discussed.     

Phenols in whisky

Summary Twelve volatile phenols were identified in whisky by combined gas chromatography-mass spectrometry. Of these phenols 2,4-dimethylphenol was found for the first time in the aroma of whisky. The content of phenol, o-, m-, and p-cresol, guaiacol, p-ethylphenol, p-ethylguaiacol and eugenol in whiskies originating from different countries was determined by gas chromatography as their 2,4-dinitrophenyl ethers using electron capture detection. The results show that Scotch whiskies differ from others in the content of o-, m-, and p-cresol. The odour threshold values of phenols studied were determined in a 10% (v/v) ethanol-water mixture and in some cases also in the whiskies. Cresols have been found to make contribution to the aroma of Scotch whisky.Presented at the 14th International Symposium on Chromatography London, September, 1982