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ANALYTICAL CURRENTS
Shrinking traps
Vapor-sensing zeolite
Optical methods for vapor sensing are Ion trap mass spectrometers are already relatively common; however, only reamong the smallest around. Now William cently have optical sensors been designed B. Whitten and co-workers at Oak Ridge National Laboratory are making them even to detect multiple analytes. Thomas Bein and Julia L. Meinershagen of Purdue Unismaller—one-thousandth the size of conversity report on the development of a ventional ion traps. multianalyte optical sensor that incorpoThe cylindrical ring electrode, which rates the solvatochromic dye Nile red into has a radius of 500 um, was made simply highly siliceous zeolites. Restricting Nile by drilling a hole in a stainless steel plate. red into a zeolite host creates a system Planar end caps—either stainless steel that combines the shape selectivity of the sheets or mesh—were separated from the ring electrode wiih Teflon tape. The entire zeolite with the chemical sensitivity of the solvatochromic dye. trap assembly was mounted in a vacuum chamber with an electron multiplier for Nile red was incorporated into the detecting the stored ions. Helium buffer zeolites by inclusion synthesis and by Incorporation of Nile red in zeolite by gas and sample vapors were introduced inclusion synthesis. adsorption from solution. Four zeolite into the trap through needle valves. Samhosts were used in the adsorption ples were ionized with pulses from an experiments—SiY [Na6(Si186AlB0S84)], result indicates that the dye remained Nd:YAG laser. The ion trap was operated in NaY [Na57(Sii35Al570384)], ZSM-5 close to the surface when adsorbed but the mass-selective instability mode, and the [NaM(AlMSi96_„0192)],andLTA was incorporated deeper into the crystal accessible mass range with the particular rf [(Na12(Al12Si12048))8]. No Nile red was by inclusion synthesis. cunplifier w3.s 30-400 Da. observed to be associated with ZSM-5 and The dye/zeolite SiY ensemble preLTA; however, both inclusion synthesis pared by inclusion synthesis showed draThe miniature ion trap was used to and adsorption in SiY yielded similar aver- matic shifts in the reflectance spectra analyze toluene, chlorobenzene, and age loadings of about 1 Nile red in 20 zeo- upon exposure to ethanol, instantly 1-chloronaphthalene. Spectra were averlite supercages. Zeolite/dye ensembles changing colors from blue to pink. A aged over seven scans of the ring elecprepared by adsorption methods changed color change to purple was observed trode. The authors attribute much of the color rapidly in the presence of air On upon exposure to acetone vapors, and no peak width to jitter from scan to scan and the other hand, those prepared by inclucolor change was observed upon expothe time constant of the preamplifier. In sion synthesis were stable under atmossure to hexane vapors. (/. Am. Chem. addition, a single-scan spectrum of tolupheric conditions for several days This Soc. 1999,121, ,48-49) ene was recorded. Mass peaks with halfwidths of 0.25 Da were observed. However, the mass uncertainty caused by jitter limited the mass accuracy to approximately 1 Da. (Rapid Commun. Mass Spec- Immunoaffinity-based SPE with GC trom. 1999,13, 50-53) Immunoaffinity-based sample enrichtaming aniibodies raised against tnazine. ment combined with LC has been used After trace enrichment, the analytes with great success for detecting drugs were desorbed and recollected (.using an or pollutants in aqueous samples. Jens acidic buffer) on a reversed-phase carDalliige and colleagues at Vrije Univertridge coupled to the gas chromatositeit (The Netherlands) evaluated graph. Following cleanup, ethyl acetate whether the same approach can be used was used to transfer the sample online to for GC analysis. the GC. In the test system, the immunoaffiniThe system was used to analyze river ty-based, solid-phase extraction carwater, wastewater, and orange juice samtridge was coupled online to a reversed- ples. With a 10-mL water sample, detecphase cartridge, which, in turn, was con- tion limits of 15-25 ng/L and about 1.5 nected to the gas chromatograph. The ng/L are found with a flame ionization capabilities of the system were tested by detector and a nitrogen-phosphorus deanalyzing for s-triazines, which were col- tector, respectively. (J. Chromatogr., A The electrode assembly of the 500-pmlected on an extraction cartridge con1999, 830, 377-86) radius cylindrical ion trap next to a U.S. dime for size comparison. Analytical Chemistry News & Features, April 1, 1999 239 A
