news from the acs national meeting: fast, hot, and on the move
TRANSCRIPT
News
applying a fast HT. "All the information is there, provided you know the sequence with which you chopped [the ion beam]," says Zare.
The gain expected from the HT—part of which is attributable to the collinear arrangement and part of which is generated by the multiplexing—is in the range of a factor of 10-100. At the ACS meeting in Boston in August, Zare reported experimental evidence that the
gain was just as theory had predicted "The thing that makes [HT-TOFMS]
potentially so appealing is that [the setup] is no different from [conventional] time of
flight," says Zare. "All you need is a grid and a computer. The grid can potentially be made very cheaply, and you need a computer anyway."
"I'm really taken with [the Hadamard transform]," Zare says. "Once you understand it, it's so amazingly simple. My hope is that lots of people will use this in the future." He hopes to interest manufacturers of TOF mass spectrometers in the technique. He imagines being able to multiplex sources through a single grid and, thus, run many samples simultaneously. "In TOF mass spectrometry, you pay for the vacuum system. Why use this big vacuum system for just one beam? Why not use 10 beams or 100 beams and get the same information out? You'd get 10 or 100 ttmes [higher] throughput." Celia Henry
Hadamard transform TOFMS experimental setup.
NEWS FROM THE ACS NATIONAL MEETING
Alan Newman reports from Boston.
Fast, hot, and on the move Over the past few years, fast GC has grown in sophistication, and now Ed Overton and his research group at Louisana State University have moved the technique one step further by creating a small yet versatile instrument. Informally dubbed the "shoe-box GC", Overton's system weighs just 15 lbs, measures 8 x 11 x 14 in., includee three electronic pressure controllers, and carries two GC columns and detectors in parallel. It can be configured as a portable GC. The key to the system, says Overton, is obtaining precise and reproducible fast temperature programming at rates as high
20 °C/s. According to Overton, the fast tempera
ture changes arise from the system's low thermal mass. "You don't want to heat an oven, just the column," he reports. Two "off-the-shelf', 100-um i.d., 1-m long GC columns are wound around each other like a double helix. The combination—along with a heater and sensor wires—is loaded into a fiberglass sheath measuring less than 1-mm in diameter. This arrangement isolates the heating and provides the rapid temperature changes without cold spots that could broaden peaks.
Samples are fed into a conventional heated inlet and then trapped onto a solid sorbent such as Tenax. Rapid thermal des-orption injects the analytes onto the two columns. According to Overton, with programmable temperature changes of 5 °C/ s, volatile hydrocarbons up to C10 need less
than 20 s to elute, and semi-volatile compounds up to C2o take less than 1 min. Coelutions are no problem because of the dual-column design; peaks that do not separate on oTif* column C3.n
be identified from the chro-matogram of the second. Or, the two chromatograms can be used ss fingerprints for compeex materials.
Cycle times are under 5 min., and Overton has run up to 80 samples, with blanks, in one day. More
over, the system handles various techniques such as purge and trap, solid-phase microextraction, and pyrolysis. The instrument design also allows back-flow cleaning of the entire analytical train, and Overton reports that as a result columns have long lifetimes.
The current design accommodates temperatures up to 250° C, but Overton is looking at increasing that value to 350° C. Hydrogen gas consumption with the dual flame ionization detectors is typically around 30 mL/min, says Overton, which should allow days of field work with a typical gas cylinder. The instrument, now called microFast GC2, has just been commercialized under the auspices of start-up company Chromalytics.
Problem-based learning A recent report arising from NSF-sponsored workshops advocates that analytical chemists introduce problem-based learning into their undergraduate courses (Anal. Chem. 1998, 70,176 A-77 A)) Although the concept has been discussed in education circles for years, to most analytical chemists this is a new idea. At the ACS meettng several practitioners of problem-based instruction shared their experiences. Several more examples will appear as feature articles in Analytical Chemistry.
The shoebox GC next to a standard Hewlett-Packard instrument.
640 A Analytical Chemistry News & Features, October 1, 1998