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other techniques show little signal variation. Normalized acoustic spectra, obtained by fast Fourier transformation of the pulsed heat reSol-gel materials can be used in applications rangingfromoptical elements and in- sponse during the first (liquid) phase and the tegrated optical devices to antioxidant, second (polymerizaanticorrosion coverings, and composite tion) phase of the evoluand biomedical materials. Control of the tion of the sol-gel shows process (i.e., control of the aging period and the rheology of the final product) by progressive shifting of the acoustic resonance of which sol-gel materials are formed althe gel structure. lows gels to be prepared in a variety of shapes, including bulk systems, percoThe photoacoustic lated materials, films, or fibers. Roger M. method can also be used Leblanc and Germain Puccetti of the Unito visualize the evoluversity of Miami have used pulsed photo- tion of different species, acoustic spectroscopy to investigate the such as polymers of difsol-gel transition of two classical sol-gel ferent lengths, as well systems: based the tetramethoxy- as changes in macrosilane precursor and one based on titaniscopic gel properties um (TV) butoxide such as viscosity, fractal dimension, average moThey found that measurement of the lecular weight, and light acoustic response spectrum of a sol-gel transmittance. (J. Pkys. material during the transition permits monitoring of variations before and after Chem. 1996 100 17311 37) the gelation point, periods for which
Monitoring the gelation process of a sol-gel
Normalized acoustic cpectra of the pulsed heat response of the liquid phase (top) and the polymerization phase (bottom) of the evolution of the titanium-based sol-gel.
Basing separation on isotopic chirality The recognition of enantiomers is essential for many biochemical processes, and various chromatographic techniques have been developed for separating optical isomers. Compounds whose chirality results from isotopic substitution, however, are extremely difficult to separate using Separation of diastereomers of methyl chromatographic techniques. Nobuo 3-phenyl-3-phenyl-d5-glycidate (1 -4) Tanaka and colleagues at the Kyoto In- based on isotopic chirality. stitute of Technology Qapan) and the Nacalai Tesque (Japan) have separated diastereomers of methyl 3-phenyl-3fractionated by recycle chromatographenyl-rfr-glycidate using reversedphy on 10-mm i.d. semipreparative colphase LCbased on the isotopic chiralumns and separated into two peaks ity provided by the presence of phenyl representing the individual enantiand phenyWr groups of the two omers using a chiral stationary phase. As a cross check, the researchers first chiral centers' Recycle chromatography using four separated the (-) and (+) forms on the 15 cm x 6 mm i.d. columns packed with chiral stationary phase followed by separation into four individual stereo5-um C18 silica in 65% methanol reisomers by reversed-phase LC. They sulted in separation of a mixture of note that true recognition of isotopic methyl 3-phenyl-3-phenyWr,-glycidate chirality will require a chiral stationary into two peaks, presumably representphase with very high efficiency. (J. ing the two diastereomers, in 18 cycles. Each of the two peaks was then Am. Chem. Soc. 1196,118, 759-62) 234 A
Analytical Chemistry yews & &eatures, April 1, 1,96
ESI-FT-ICRMS gets cereus The B. cereus group includee she organisms B. anthracis and B. .ereus, which ara human pathogens, and B. thuringiensisi which is used as a biological pesticide. This group is highly conserved both phenotypically and genetically, and differentiation of its members using molecular methods is difficult. However, because there is some variability in the ribosomal spacer region, PCR amplifications can be used to generate double-stranded productsfromthis region that are unique to the B. cereus group. Analysis of these eroducts (of a size amenable to MS) by electrophoresis takes several hours which prompted Alvin Fox Richard D. Smith and colleagues at the University of South Carolina and Pacific Northwest National Laboratory to investigate the use of ESIFT-ICRMS as a rapid way to detect these PCR products A 105-bp nucleotide portion of the ribosomal spacer region in B. cereus and B. thuringiensis was amplified by PCR and analyzed by ESI-FT-ICRMS and gel electrophoresis. The mass measurements for the two bacteria, obtained in seconds by MS, matched the theoretical mass, within experimental error, obtained in hours by
