Important
News for NMR
Spectroscopists
COMPUTER
NEW LOW-COST
USES AVERAGING TECHNIQUE TO GREATLY INCREASE SIGNAL-TO-NOISE RATIO CAT 400 NMR PERMITS ON-LINE DETECTION OF TRACI QUANTITIES OR SAMPLES OF EXTREMELY HIGH DILUTIOt MNEMOTRON'S Computer of Average Transients — CAT 400 NMR * — offers significant new instrumentation for NMR Spectroscopy. Up to now the investigator has been severely limited in de tecting trace quantities or samples of extremely high dilution. Random noise masking the desired signal has hampered the detection of resonance peaks for adequate identification.
TYPICAL RESULTS ACHIEVED THROUGH USE OF CAT 400 NMR
WITHOUT CAT 400 NMR
WITH CAT 400 NMR
CAT 400 NMR greatly increases the signal-to-noise ratio by extending the period over which measurement is made. This extension is accomplished on-line through use of an averag ing technique. Analog signal amplitudes masked by low-frequency noise are converted into digital counts that are stored in 400 memory channels, starting from a known reference point. The counts in each memory channel are added; the components phaselocked to the reference point are isolated from the out of phase random noise, which cancels out. The Spectroscopist is thereby provided with a clearly defined signal of the spectra under investigation. The CAT 400 NMR includes circuitry providing for the elec tronic sweep of the spectrometer magnetic field, permitting synchronization of the spectral sweep along with the CAT analysis. In addition, a search ramp feature establishes a reference pulse initiating CAT NMR operation. The reference pulse is obtained in conjunction with the search ramp by the use of sideband techniques. It may therefore be adjusted to occur at any point on the spectrum for the enhancement of a specific portion of the overall spectral pattern. Computed results can be read out in analog form back onto the plotter associated with the spectrometer — or in digital form for further computer analysis.
WITHOUT CAT 400 NMR •
WITH CAT 400 NMR
Shown above are "C patterns of the olefinic hydrogens from "C in natural abundance. [P. Laszlo and P. von ft. Schieyer, J. Am. Chem. Soc. 85, 2017 (1963)]. • Development of the technique for using the CAT in chemical applications of NMR and ESR is described by L. C. Allen and L F. Johnson, J. Am. Chem. Soc. 85, 2668 (1963). These authors summed 2500 spectral traces in CAT 400 and ob tained a resultant spectrum for 0.004% ethyl benzene in CCU having the same appearance found for a 0.2% solution with a single trace. a 0. Jardetzky, N. G. Wade and J. J. Fischer, Nature, 197, 183 (1963) report detection of 0.005 M DPN (diphosphopyridine nucleotide) in D20 (alcohol dehydrogenase) — an experiment that illustrates the importance of the averaging technique in allowing the investigator to work with concentrations usu ally found in biological systems.
The entire averaging process is performed within the instru ment itself. Yet CAT 400 NMR is portable, weighing just 35 pounds and occupying less than one cubic foot of bench space. And it's low in cost! 'Patented
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