Development of monolithic enzymatic reactors in glass microchips for the quantitative determination of enzyme substrates using the example of glucose determination via immobilized glucose oxidase

A one-step procedure for the immobilization of glucose oxidase in fused-silica capillaries and in glass microchips was developed based on enzyme entrapment in a polyacrylamide-based monolithic column. The inner capillary surface was silanized with gamma-methacryloxypropyltrimethoxysilane (gamma-MAPS) to allow covalent binding of the gel to the surface. The composition of the polymer was optimized to prevent the formation of bubbles, allow liquid transportation by electroosmotic flow and to maintain the enzymatic activity. These requirements resulted in the addition of polyethylene glycol and poly(acrylic acid) to the acrylamide mixture. The gel containing the enzyme was formed in situ in the capillaries, respectively, in one channel of the microchip. In the microchip, it was limited to the sample injection channel by accordingly controlled silanization of the inner capillary surface. Glucose was detected via the amperometric determination of hydrogen peroxide. A linear correlation between signals and glucose concentration was observed from 0.05 to 1.1 mM glucose with a correlation coefficient of 0.999. The enzymatic monolithic microreactor showed no loss of activity during 8 h of continuous use and during storage in the running buffer at 4 degrees C for about 2 months. Interferents, such as ascorbic acid, were separated from the analyte electrophoretically, so that glucose could be quantified in diluted juices.     

Die fluorimetrische Bestimmung des Gesamtcatecholamingehaltes im Urin

Ohne Zusammenfassung     

Strong field quantum path control using attosecond pulse trains

We show that attosecond pulse trains have a natural application in the control of strong field processes. In combination with an intense infrared laser field, the pulse train can be used to microscopically select a single quantum path contribution to a process that would otherwise consist of several interfering components. We present calculations that demonstrate this by manipulating the time-frequency properties of high order harmonics at the single atom level. This quantum path selection can also be used to define a high resolution attosecond clock.     

Gas-phase thermolysis of sulfur compounds. Part VIII. Chloromethyl allyl,cyanomethyl allyl, 1-cyanoethyl allyl and neopentyl allyl sulfides

The pyrolyses of four alkyl allyl sulfides with substituents on the α? C atom of the alkyl moiety have been studied in a stirred-flow system over the temperature range 340-400°C and pressures between 2 and 12 torr. The only products formed are propene and thioaldehydes. The reactions showed first-order kinetics with the rate coefficients following the Arrhenius equations: Chloromethyl allyl sulfide: Cyanomethyl allyl sulfide: 1-cyanoethyl allyl sulfide: Neopentyl allyl sulfide: The effects of these and other substituents on the reactivity is discussed in relation with the stabilization of a polar six-centered transition state. The results support a non-concerted mechanism where the 1–5 α? H atom shift is assisted by its acidic character.     

Die Bestimmung der 17-Ketosteroide im Plasma

Ohne Zusammenfassung     

Zur colorimetrischen Sulfatbestimmung

Ohne Zusammenfassung     

Determination of biogenic halogenated methyl-phenyl ethers (halogenated anisoles) in the picogram m -3 range in air

Halogenated anisoles (methyl-phenyl ethers) appear to be ubiquitous organic trace compounds in the environment. An analytical method is presented for analyzing the altogether 134 congeners of chloro-, bromo- and mixed bromochloro-anisoles on an isomer-specific basis in air. High volume sampling (20 m³ per hour) is carried out by adsorption, using a mixture of silica gel 60 and ENVI-Carb. The preseparation of the anisoles is achieved by NP-LC on Florisil (a magnesium silicate). The interference by volatile n-alkyl nitrates in the electron-capture detection can be avoided by a LC-preseparation on a carboneous phase. The isomer-specific separation and detection is performed by HRGC-ECD and HRGC-MS-SIM. A structure-specific systematic numbering of the 134 congeners of the chloro-, bromo- and bromochloro-anisoles is suggested. The retention data are given of 16 chloroanisoles, 10 bromoanisoles and 27 bromo-chloroanisoles on three stationary phases with different polarity.