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