RI DETECTION IN THE NANOGRAM RANGE
Focus
Carbohydrate and fat analysis
MATRIX ISOLATION INTERFACE FOR GC/FT-IR High sensitivity The Tecator Interference Refractometer has a detec tion limit of 10 nanograms N o calibration Absolute RI-values year after year, without any conventional calibration procedures. Large dynamic range Easily interchangeable measuring cells, enabling analysis from 10 ng up to 500 μg. The Tecator Liquid Chromatograph This HPLC system features: • Precision controlled column compartment. • Thermostat for eluent reservoir and refracto meter. • High-frequency pump with pulse damper. Please call or write for Application Notes and product information.
A development of note at the Pitts burgh Conference earlier this year was Mattson Instruments Inc.'s introduc tion of Cryolect, a gas chromatography-Fourier transform infrared spec trometry (GC/FT-IR) interface based on the principle of matrix isolation, a line-narrowing technique that results in very high resolution, high sensitiv ity IR spectra. Although research on matrix isolation dates all the way back to the mid-1950s, Cryolect is the first commercial analytical device based on the technique. Gerald T. Reedy of Argonne Na tional Laboratory is the inventor of Cryolect, and Mattson Instruments is exclusive distributor for the product, although the interface can also be used with non-Mattson FT-IRs that
Focusing Mirrors
meet certain specifications. The de vice is actually manufactured by Cryo lect Scientific Corp., a company set up by Reedy to bring the device to mar ket. In operation, the GC effluent (He with 1-2% Ar added) is split in two (see Figure 1). One part goes to a con ventional GC detector. The other part is admitted to the Cryolect interface, where Ar atoms and sample molecules condense on a rotating mirrored cylin der that has been cooled to 12 K; He atoms do not condense at this tem perature and are pumped away. The frozen matrix, a cryogenically trapped version of the chromatogram, will re main on the cylinder as long as the temperature is maintained at 12 K. After the chromatographic run is
Vacuum Chamber IR Detector
Optical Beam Gas Chromatograph GC Oven Focusing Mirror Splitter
Collection Disk
GC Transfer Line
Open-Split Interface
tecator
- Flame Ionization Detector
Box 70 S-263 01 Hoganas, Sweden Tel: (+42)423 30 Telex: 72695
Figure 1 . Diagram of Mattson's Cryolect G C / F T - I R interface CIRCLE 208 ON READER SERVICE CARD
936 A · ANALYTICAL CHEMISTRY, VOL. 56, NO. 8, JULY 1984
Injector
Focus complete, the operator selects peaks of interest from the chromatogram, and the Cryolect cylinder is positioned by a computer so each peak of interest can be scanned sequentially by F T IR. Each peak may be observed for as long as desired before the cylinder is moved to place the next peak in the IR beam path. IR band broadening and band shifting, usually caused by intermolecular bonding and rotational absorption of the sample molecules, is prevented in the Cryolect system, not only by the presence of the argon matrix, which isolates each analyte molecule, but also by the cryogenic temperature level of the cylinder. Thus, GC/FT-IR spectra obtained with a matrix isolation interface exhibit higher resolution than with lightpipe systems. The sensitivity of Cryolect GC/FTIR is also higher, since extended observation times are possible with the Cryolect device. According to Earl L. Wehry, Jr., of the University of Tennessee, who wrote a May 1979 survey article on matrix isolation (Anal. Chem. 1979,51, 643-56 A), "A gasphase peak shoots through a light pipe very quickly, causing certain sensitivity problems. But the low-temperature
matrix just sits there until you warm up the cryostat, making it possible to do signal averaging to improve the sensitivity." Dave Mattson, president of Mattson Instruments, says that "the market for Cryolect is where sensitivity is all-important." The company claims that the sensitivity of Cryolect GC/FT-IR is, in some cases, higher than that of GC-mass spectrometry (GC/MS), a widely popular technique known for its sensitivity. In addition, with matrix isolation, isomers that are structurally very similar can be easily distinguished, something that GC/MS may have trouble with. "I guess the question in the long run," adds Wehry, "is how matrix isolation GC/FT-IR stacks up in competition with GC/MS, which is the obvious competitor, particularly in terms of sensitivity." The Cryolect device "has possibilities," continues Wehry. "But I was surprised that the cost was so high because, given that GC/MS is so firmly entrenched, one potential advantage of an optical spectrometric interface over mass spectrometry is lower cost. I'm a little surprised that they didn't avail themselves of that advantage when they came out with this first in-
strument." The Cryolect interface is currently priced at $104,000. "For any new technique, the costs are going to be high," Dave Mattson replies. "If we were able to sell 100 of these the first year, however, the price could come down." And inventor Reedy explains that the cost of the hardware that goes into the interface in relation to its price is higher than for comparable analytical instruments. There are a number of components that add significantly to the price of Cryolect, including a turbopump, an expensive stepper motor, micro-IR optics, a remote mercury cadmium telluride detector, and the cryogenic refrigerator. Speaking of the prospects for further commercialization of matrix isolation in general, Wehry points out, "There are all kinds of possibilities for other types of optical spectroscopic measurements other than IR that could presumably be exploited—such as fluorescence, which can be very sensitive—providing there is some interest that develops in this new accessory. The field could presumably develop in those directions as well." Stuart A. Barman
STEP UP COST-EFFICIENCY MCI Has Just the Moisture Measurement System You Need. Performance takes a big step forward in our new microprocessor-control CA-05 Moisture Meter/VA-05 Water Vaporizer system with built-in printer. Moisture measurement is fully automatic. High coulometric Karl Fischer titration accuracy and sensitivity combine with wide mode/calculation functions for amazing application versatility. Advanced features include an airtight titration cell, 16-digit display, automatic calendar and optional electronic balance/computer interfacing. Write for complete details today.
MITSUBISHI CHEMICAL INDUSTRIES LIMITED Instruments Dept-, Mitsubishi Bldg., 5-2, Marunouchi 2-chome, Chiyoda-ku, Tokyo 100, Japan Telex: J24901 Cable Address: MBISHICHEMICAL TOKYO Tel: (03)283-6715 CIRCLE 138 ON READER SERVICE CARD
938 A · ANALYTICAL CHEMISTRY, VOL. 56, NO. 8, JULY 1984
