PubMed · 8746677
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K D Altria. 1996. Method development/optimization.. https://doi.org/10.1385/0-89603-315-5%3A29
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Polypyrrole (PPY) and poly-N-phenylpyrrole (PPPY) films were prepared and applied for solid-phase microextraction (SPME). The extraction properties of the new films to volatile organic compounds were examined using an SPME device coupled with GC-flame ionization detection. A PPY-coated capillary was applied for in-tube SPME to evaluate its extraction efficiency towards less volatile compounds and ionic species. The porous surface structures of the films, revealed by scanning electron microscopy, provided high surface areas and allowed for high extraction efficiency. Compared with commercial SPME stationary phases, the new phases showed better selectivity and sensitivity toward polar, aromatic, basic and anionic compounds, due to their inherent multifunctional properties. In addition, PPY and PPPY films showed different selectivity to various groups of compounds studied, indicating that the selectivity of the films could be modified by introducing a new functional group (phenyl in PPPY) into the polymer. For in-tube SPME, the PPY-coated capillary showed superior extraction efficiency to commercial capillaries for a variety of compounds, demonstrating its potential applications for a wide range of analytes when coupled with HPLC. The sensitivity and selectivity of the films for SPME could be tuned by changing the film thickness. These results are in line with both the theoretical expectations and the results obtained by other methods, which indicate not only that PPY films can be used as new stationary phases for SPME. but also that SPME method may provide an alternative tool for studying materials like polypyrrole.
Volatile components of uncooked Khao Dawk Mali 105 brown rice were extracted using indirect steam distillation under reduced pressure and controlled temperature in order to prevent cooking. Analysis of the fresh extract by capillary gas chromatography-mass spectrometry revealed that there were >140 volatile constituents. Among these, 70 volatiles were identified, including 2-acetyl-1-pyrroline (2AP), a key aroma compound of cooked rice. Further study concentrated on an improved method for the quantification of 2AP in uncooked brown rice. The method was simplified by utilizing a solvent extraction procedure. Quantitative analysis was performed using a capillary gas chromatographic system employing a flame ionization detector with the aid of a more selective column, CP-Wax 51, for amines. This improved chromatographic system had remarkable detection sensitivity for 2AP in the rice extracts so that 2AP in an extract of only 0.5 g of uncooked Khao Dawk Mali 105 brown rice could be detected.
This article is devoted to an overview, comparison and discussion of recent results (both theoretical and experimental) about lateral capillary forces. They appear when the contact of particles or other bodies with a fluid phase boundary causes perturbations in the interfacial shape. The capillary interaction is due to the overlap of such perturbations which can appear around floating particles, vertical cylinders, particles confined in a liquid film, inclusions in the membranes of lipid vesicles or living cells, etc. In the case of floating particles the perturbations are due to the particle weight; in this case the force decreases with the sixth power of the particle size and becomes immaterial for particles smaller than approximately 10 microm. In all other cases the interfacial deformations are due to the particle wetting properties; the resulting 'immersion' capillary forces can be operative even between very small particles, like protein globules. In many cases such forces can be responsible for the experimentally observed two-dimensional particle aggregation and ordering. An analogy between capillary and electrostatic forces enables one to introduce 'capillary charges' of the attached particles, which characterize the magnitude of the interfacial deformation and could be both positive and negative. Moreover, the capillary interaction between particle and wall resembles the image force in electrostatics. When a particle is moving bound to an interface under the action of a capillary force, one can determine the surface drag coefficient and the surface viscosity supposedly the magnitude of the capillary force is known. Alternative (but equivalent) energy and force approaches can be used for the theoretical description of the lateral capillary interactions. Both approaches require the Laplace equation of capillarity to be solved and the meniscus profile around the particles to be determined. The energy approach accounts for contributions due to the increase of the meniscus area, gravitational energy and/or energy of wetting. The second approach is based on calculating the net force exerted on the particle, which can originate from the hydrostatic pressure, interfacial tension and bending moment. In the case of small perturbations, the superposition approximation can be used to derive an asymptotic formula for the capillary forces, which has been found to agree well with the experiment. Capillary interactions between particles bound to spherical interfaces are also considered taking into account the special geometry and restricted area of such phase boundaries. A similar approach can be applied to quantify the forces between inclusions (transmembrane proteins) in lipid membranes. The deformations in a lipid membrane, due to the inclusions, can be described theoretically in the framework of a mechanical model of the lipid bilayer, which accounts for its 'hybrid' rheology (neither elastic body nor fluid). In all considered cases the lateral capillary interaction originates from the overlap of interfacial deformations and is subject to a unified theoretical treatment, despite the fact that the characteristic particle size can vary from 1 cm down to 1 nm.