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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
gel electrophoresis. The researchers note that although precision needs to be improved, this preliminary result indicates the potential use of ESIMS to analyze PCR products on a rapid time scale, with potential for medical and taxonomic applications. (Rapid Commun. Mass Spectrom. 1996,10,29-35)
ESI-FT-ICFt mass spectrum of the PCR product ofB. thuringiensis with tentative charge states indicated. (Adapted witw permission ffom John Wiley & Sons.)
Sample loss in electrothermal vaporization
Nonradioactive l a b e l i n g of RNA Although the necessity of nonradioactive labeling methods for natural RNA has been known for more than a decade, a convenient method of attach ing such labels has not yet been described. Gabor L. Igloi of the University of Freiburg (Germany) has synthesized a modified ribodinucleotide analogue of the commonly used ra dioactive [32P]pCp. Called pSEEp, the new reagent has a 3'-terminal primary amino group that can serve as a point of attachment for a variety of nonradioactive labels such as fluorescein. Igloi used a T4 RNA ligase catalyzed reaction to attach the tagged dinucleotide to natural RNA and analyzed the resulting RNA using a fluorescence-based DNA sequencer. The effects of ribose oxidation and aminoacylation on the ligation reaction were
plasma. Despite these advantages, analyte loss can still occur in the transport tube. James A. Holcombe and Christopher M. Sparks of the University of Texas and Thomas L. Pinkston of SEMATECH have measured the amount of material reElectrothermal vaporization has several tained in the transport tube as a function of advantages over nebulization as a sample introduction technique for ICPMS, includ- the mass of sample vaporized. ing increased sampling efficiencies, Because physical carriers such as NaCl lower detection limits, reduced sampleare often added to the system to enhance volume requirement, and reduced interfer- condensation by providing additional nuences from matrix constituents in the cleation sites, the researchers first determined the percent of NaCl retained and then the percent of Ag retained, with and without NaCl present. Approximately 10% of the NaCl carrier remained in the transport tube. When the Ag was vaporized with NaCl, approximately 610 % of theAg was retained depending on the type of tubing. These numbers closely paralleled the amount of c cirrier rc_ tained which indicated that the Ag was probably transported on the carrier When Ag was vaporized alone onlv 1-3 % remained Effect of various maases sf NaCl carrier on ionization on in the tube (AM Stoersilver. .Adapted dith permission of the Society for Applied trosc.996 50 86-901 Spectroscopy..
Structure of the dinucleotide pSEEp and its fluorescent derivative ZFpSEEp. (Adapted with permission of Academic Press.)
also studied. He suggests that any procedure depending on detection or targeting tagging of RNA can be adapted for use with pSEEp and its corresponding biotin and phenanthroline derivatives. (Anal. Biochem. 1996,233,124— 29)
Antarctic aerosol particles by LAMMS Because of its remoteness from human activity, the Antarctic is an ideal site for monitoring changes in the global environment. The Antarctic atmosphere is sensitive to changes in climate and air quality, including the effects of aerosol particles that scatter solar light and contribute to cloud formation. Earlier studies of particles have concentrated on size distribution and elemental composition using bulk analysis techniques, rather than on obtaining information on individual particles. Keiichiro Hara and colleagues at the Science University of Tokyo (Japan) Nagoya University (Japan) and the National Institute of Polar Research Oapan) used reflection laser microprobe MS (LAMMS) to clarify the seasonal behavior of Antarctic aerosol particles over the course of a year Because LAMMS suffers from poor reproducibility of spectrum intensity the researchers used the relative abundance of characteristic peaks to quantitate their results Matrix effects were eliminated bv analyzing a fixed number of individual nar tides and defining the relative abun dance of the species as the ratios of the frequency of detected characteristic peaks 2
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for a specific component (e.g., Pb) to the total number of analyzed particles.
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