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TOF spectrometer measures up E. C. Montenegro and colleagues at Pontif ícia Universidade Católica do Rio de Janeiro (Brazil) have designed a timeof-flight (TOF) spectrometer that performs absolute measurements of the yields of ionic species in the gas phase produced by charged particles. Their TOF spectrometer uses an extended target gas cell, which has a volume large enough to ensure laminar flow of the gas through the cell apertures. The use of a gas cell also allows transmission and coincidence measurements to be made under the same conditions, the researchers say. They verified the spectrometer’s performance through absolute measurements of multiple ionizations of noble gases by charged particles. They obtained an m/m value of 62, which was enough to observe the xenon isotopic composition. Typical times of flight recorded were ~0.3 µs for He+, ~1.0 µs for Ne+, and ~3.0 µs for Xe+. The spectrometer is located inside a stainless steel vacuum chamber and consists of a flight-tube assembly positioned at 90º to the incident beam direction. Positive ions are extracted from the extended gas target and then accelerated down a 94-mm-long, stainless steel drift tube. At the end of the spectrometer, there are two microchannel plate (MCP) detectors mounted in the chevron configuration. The researchers placed a mesh between the end of the TOF tube and the MCP detectors to stop electrons emitted from the MCP surface from going into the TOF tube. The spectrometer also has a two-stage accelerating electric field. The first 960V/cm-dc electric-field stage has a plate– grid system with the primary beam passing through its middle. The second electric-field stage, at 3600-V/cm dc, is a lens designed to weakly focus the recoil ions in a 4-mm-diam aperture placed 3.7 cm from the interaction region. This aperture is the only vacuum connection between the MCP detectors and the gas cell. (Rev. Sci. Instrum. 2002, 73, 2369–2374)
Nanoparticle HPLC One way to achieve faster separation times and higher efficiencies in LC is to reduce the diameter of the
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chromatographic column packing material. Simple? Not really, because the column pressure required for such a separation rises quickly as particle size drops. Luis Colón and José Cintrón of the State University of New York–Buffalo report the synthesis of organosilica nanoparticles and their first use with ul-
Going from (left) 5000 to (right) 50,000 psi significantly shortens the analysis time for a separation using nanoparticles. Peak 1, ascorbic acid; 2, hydroquinone; 3, resorcinol; 4, catechol; and 5, 4-methylcatechol. (Adapted with permission. Copyright 2002 Royal Society of Chemistry.)
trahigh pressure LC (UHPLC).
conditions of 50,000 psi. Analysis time for
The nanoparticles were synthesized
a test solution dropped from 25 min to ~3
with a sol–gel process in a single step,
min, respectively, and column efficiency
yielding a uniform 670-nm-diam (±40 nm)
jumped from 130,000 to 500,000 plates/m.
material. Columns packed with the parti-
The column was also shown to withstand
cles were run at a conventional HPLC
extreme pH conditions for extended peri-
pressure of 5000 psi and under UHPLC
ods of time. (Analyst 2002, 127, 701–704)
Top and side views of the chamber and gas cell of a TOF mass spectrometer. (Adapted with permission. Copyright 2002 American Institute of Physics.)
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