Instrumentation
•
Convenient bench scale
·
units provide complete
.
-
tacilities tor applying heat and pressure to any •
chemical reaction. One and two liter sizes.
Pressures to 2000 psig. Temperatures to 350° C.
Automatic temp, control, Available In all principal corrosion resistant alloys.
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Ask for Specification 4S00
PARR INSTRUMENT COMPANY Moline, Illinois 61265
211 Fifty-Third St.
Circle Nc. 47 on Readers’ Service Card
LOW PRICES ON QUALITY
FFT (fast Fourier transform) computer programs available, one needs a signal averager and/or computer with a capacity of at least 8192 words for data storage; the word size should be at least 18 bits although 16 will do. Of course, another 4000 words of memory are needed in the computer to carry out the Fourier transformation. After the cw-nmr spectrum has been calculated, a D/A converter is needed to plot out the final cw spectrum.
ABSORPTION CELLS
In summary, the field of 13C-Ft-nmr spectroscopy is developing at a very rapid rate. Although there have been many problems, they have, for the most part, been solved. With the rapid development and ever-decreasing cost of small computers, it seems safe to predict that the time when Ft-nmr spectrometers are as ubiquitous as the cw-nmr spectrometers is not far away.
No Cemented Seams to Dissolve in Acid.
Fully Fused
down. Of course, it is necessary that the r.f. gate unit supply a coherent r.f. reference signal to drive the ring demodulator in the r.f. phase detector. The total system recovery time at 15 MHz should be 15 ^sec or less and the preamp-receiver combination should have a voltage gain of 120 db or more. The entire system should be extremely well shielded to avoid RFI problems arising from clocks in the signal averager, pulse programmer, or computer. For maximum flexibility the digitizer in the A/D converter of the computer should have at least 10 bits or more and it should have a digitizing rate of For 15 MHz at least 20 kHz or more. 13C-nmr, a writing speed of 6 kHz is required [from sampling theory one knows that to cover a spectrum of “x” Hz (in our case x = 3000 Hz), it is necessary to sample at a rate of “2 x” Hz], If one samples for 1 see (to obtain a resolution of 1 Hz), then 6000 data channels are required in which to store the data. To make use of the
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References (1) I. J. Lowe and R. E. Norberg, Phys. Rev., 107, 46 (1957). (2) J. D. Roberts, et al., J. Amer. Chem. Soc., 91, 7445 (1969); D. Grant and B. Cheny, ibid., 89, 5315-19 (1967) ; P. C.
520 types Cuvettes available
in Glass. Special Glass, Quartz. Matched Sets, specials to order.
CUVETTE WASHER-DRYER The only lest without scratching or breaking. Completely assembled (without filtering flask) $16.00 ea. way to wash and dry cuvettes
Lauterbur, in “Determination of Organic Structures By Physical Methods,” F. C. Nachod and W. D. Phillips, Eds., Vol. 2, Academic Press, New York and London, 1962, Chap. 4. Other helpful references arc given in these
CUVETTE $8.50
ADD-A-MIXER
ea.
used for adding small volumes of enzyme solution to
NEW CATALOG 70/1 AVAILABLE I
PRECISION CELLS, INC. 221 Park Ave.
·
Hlcksville,
N. Y.
11801
reaction mixtures in spectrophotometer cuvettes.
S2.50
ea.
three papers. (3) R. R. Ernst and W. A. Anderson, Rev. Sci. Instr., 37, 93 (1965). (4) A. Abragam, “The Principles of Nuclear Magnetism,” Clarendon Press, Ox-
ford,
1961.
Vol.
18
(5) E. D. Becker, J. A. Ferretti, and T. C. Farrar, J. Amer. Chem. Soc., 91, 7784 (1969). (6) J. Jonas and H. S. Gutowsky, “Annual Reviews of Physical Chemistry,”
(Eyring, H., Ed., Annual Re-
views, Inc., 1968). Circle No. 54
112 A
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on Readers’
Service Card
ANALYTICAL CHEMISTRY, VOL 42, NO. 4, APRIL 1970
