Microfluidic devices have been fabricated on poly(methyl methacrylate) substrates by two independent imprinting techniques. First-generation devices were fabricated using a small-diameter wire to create an impression in plastics softened by low-temperature heating. The resulting devices are limited to only simple linear channel designs but are readily produced at low cost. Second-generation devices with more complex microchannel arrangements were fabricated by imprinting the plastic substrates using an inverse three-dimensional image of the device micromachined on a silicon wafer. This micromachined template may be used repeatedly to generate devices reproducibly. Fluorescent analtyes were used to demonstrate reproducible electrophoretic injections. An immunoassay was also performed in an imprinted device as a demonstration of future applications.

We describe specifications for high-purity 4-nitrophenol, which is suitable for spectrophotometric standardization. Such a reference material is needed in clinical enzymology to establish the proper molar absorptivity of 4-nitrophenol under final reaction conditions, particularly for measuring alkaline phosphatase activity in human serum. Some lots of 4-nitrophenol available commercially met these specifications, but several did not. The latter can be purified to meet our specifications by recrystallization or sublimation. The molar absorptivity of 4-nitrophenol (35 μmol/L) IN 10 mmol/L NaOH at 25 °C at 401 nm is 18380 +/− 90 L.mol−1.cm−1.

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A simple, rapid and selective method for the determination of Crlll and Crvl in natural waters by ion-pairing high-performance liquid chromatography (HPLC) with flame atomic absorption spectrometry (FAAS) as the method of detection is described. The samples and standards are acidified with glacial acetic acid to a pH of 3.1-3.2. The eluent consists of dilute tetrabutylammonium phosphate also acidified to a pH of 3.1-3.2.Separation is accomplished on a 4 cm long column packed with polymeric CI8 material. The effluent from the column is fed directly into the atomic absorption spectrometer.Chromium(V1) added to pond water began to decay to CrIll immediately upon addition. The rate of decay depended on the level of suspended organic material in the water. The recovery of the sum of both Ct -111 and CrVl species in 65 spiked water samples was 100.9% with a standard deviation of 6.Z0/&.

The molecular theory of rubber elasticity assumes the free energy to consist of two parts: a liquidlike free energy that is governed by intermolecular interactions and is independent of strain at constant volume and an intramolecular interaction free energy equal to the sum of the free energies of the chains making up the network. The volume increases of rubber samples as a function of their length were found to be considerably larger than predicted by the molecular theory. Therefore, contrary to common belief, the values of (∂E/∂L)V,T might not be related solely to changes in intramolecular interactions with extension. Also, the usual procedure to obtain values of (∂E/∂L)V,T from measurements of (∂f/∂T)p,L with the aid of the molecular theory is not correct.