MS - American Chemical Society

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Focus

Miniature Gas Chromatograph Microsensor Technology Inc. (MTI) of Fremont, Calif., is a company you probably will be hearing more about. MTI's Michromonitor, a product t h a t was exhibited at the Pittsburgh Conference earlier this year, is the first commercial realization of the gas chromatograph-on-a-chip that has been under development since the early 1970s (Anal. Chem. 1979, 51, 106668 A). And the company has other portable analytical instruments in the works. The Michromonitor is a self-contained, microprocessor-controlled, portable gas monitor t h a t contains from one to five fully independent miniature gas chromatographs (GCs). Each GC module, which includes a sample injection system and a thermal conductivity detector etched onto a silicon wafer, a carrier gas regulation system, a micropacked or capillary column, and associated electronics, is still small enough to fit in the palm of your hand. "Our miniature technology allows us to mount up to five GCs, run them in parallel, and have each one optimized for a certain subset of gases," explained Stephen C. Terry, MTFs R&D manager. What distinguishes the Michromonitor from other commercially available portable GCs is not only t h a t it contains up to five independent chromatographs, but that the operator need not be an analytical chemist or have any understanding of chromatography. "You just select up to ten analyte gases from the instrument's library, tell it to go, and it performs the analysis," said Terry. Each analytical cycle takes less than a minute. The Michromonitor contains rechargeable batteries and its own internal helium carrier gas supply for portable operation. But for fixed-location monitoring, the unit can be plugged into an ac power outlet and hooked up to a large tank of carrier gas. Results of up to 370 analyses can be stored in memory for subsequent review or print-out. The Michromonitor costs 0003-2700/84/0351-801A$01.50/0 © 1984 American Chemical Society

$10,000 to more than $20,000, depending on configuration. According to Terry, "At this point we've been able to sell far more than we can produce. We've seen interest for a number of different applications, including industrial hygiene, process control, and natural gas pipeline monitoring. In addition, we've placed a fair number of units in major chemical and petrochemical corporate R&D facilities for them to evaluate the technology and see whether or not they want to work it into some of their processes." Current M T I development efforts include minimizing the size of the Michromonitor for even greater portability. So don't be too surprised if you see the proverbial shirt pocket GC turning up at MTI's Pittsburgh Conference booth sometime soon.

MTI's Michromonitor contains up to five GCs like the one in this photo.

VG Instrumente Debute ICP/MS In our coverage of last year's Pittsburgh Conference (May 1983, pp. 6 1 1 12 A), we reported on Sciex's inductively coupled plasma-mass spectrometer (ICP/MS), the first commercial device of its kind, writing that "most seem to feel t h a t Sciex eventually will have company in the I C P / M S market." A visit to the VG Instruments booth at the '84 meeting revealed t h a t prediction to be an accurate one, as VG was showing its new PlasmaQuad, the second commercially available ICP/MS. Meanwhile, Sciex was happily preparing to ship its first I C P / M S units in April, it having taken the company longer than anticipated to get into full production. Why all the interest in ICP/MS? According to R. S. Houk of Ames Laboratory, who developed the first operating I C P / M S in conjunction with Alan Gray, Velmer Fassel, Harry Svec, and others, I C P / M S is the first tech-

nique that permits the direct, continuous introduction of an aqueous solution into a mass spectrometer for elemental analysis. Liquid chromatography-mass spectrometry (LC/MS) is still used primarily for molecular analysis. In ICP/MS, the sample is rapidly dissociated and ionized in the plasma. T h e resulting ions are then admitted through an aperture into the vacuum system of a quadrupole mass spectrometer, where a mass spectrum of the ions is obtained. The use of the ICP as an ion source makes it possible to use the whole range of conventional ICP sample introduction methods, including nebulization, hydride generation, and electrothermal vaporization. Houk expects I C P / M S to "quite possibly prove superior to emission spectrometry" in detection limits and in freedom from interferences. "Some of the elements near the center of the

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periodic chart have very rich emission spectra that can cause spectral overlap," Houk explained, "but the mass spectral isotopic patterns for those elements are much less complicated." Detection limits in ICP/MS are, in general, better than in plasma emission spectrometry. And the ICP/MS makes it possible to determine elemental isotopes and to use isotope dilution for quantitation. Will other vendors jump on the ICP/MS bandwagon? The answer is

almost certainly yes. "I have seen interest from both mass spectrometer manufacturers and emission spectrometer manufacturers," says Houk. "VG Instruments and Sciex are both mass spectrometer manufacturers, but the people who make emission spectrometers are sitting up and taking notice too. Whether they'll try building quadrupoles and vacuum systems is another matter, but they're keeping an eye on what's going on."

Follow-Up on the Ian Trap Detector While we're on the subject of new instruments discussed in last year's Pittsburgh Conference FOCUS coverage, remember the ion trap detector (ITD)? Manufactured by Finnigan MAT, the ITD (June 1983, pp. 72628 A) is a combined ion source and mass analysis device that uses radiofrequency fields to store ions. When hooked up to a gas chromatograph, the ITD provides a very inexpensive alternative to conventional gas chromatography-mass spectrometry. The ITD is still around, but, as it happens, not a single unit has been shipped. Late last year the company informed all those who had ordered ITDs that there were technical difficulties and that the shipping schedule had been suspended. "The physics involved turned out to

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be more difficult to understand than we anticipated one year ago," said Finnigan chairman and president T. Z. Chu. "We resolved the problem by going back to a very fundamental restudy of the phenomenon, and we reached a correct understanding of what's going on inside the trap. Once we understood that, the solution became very straightforward." According to Chu, "All throughout this time we received exactly two cancellations out of 100 orders, both because the funding ran out. I think that's some indication that people really want us to be successful with this product. We continue to be very optimistic about the size of the market for the ITD." Chu said that Finnigan would finally be shipping ITDs before the end of this year.