cooling of the catalyst. Disassenibly of the apparatus t o change the catalyst is rapid. Gas leakage cannot be tolerated. When the apparatus is assembled, each fitting should be tested for leakage with soapy mater or other means before turning on the heat. The injection jeptum should be tested frequently and changed as soon as a leak is detected. Leakage should be suspected as soon as knowns, which are run regularly, change retention time appreciably or diminish in intensity sharply. The columns employed in this study n-ere convenient to use because they can be operated a t room temperature. The squalane column covers the C1 to c'; range, the SE-30 column the Csto Cg range. Heating of the latter column vas necessary to avoid unduly long retention times for analyses on C9 and Cla compounds. The Pfficiency of the squalane column operating a t room temperature is about 1400 theoretical plates for the Ca to Cg hydrocarbons and about 2400 plates for heptane. ,4ny column that will best separate the products may be used. About once a rreek columns were purged by heating overnight a t 100" C. with hydrogen or nitrogen flowing through them. The use of a molecular sieve to separate branched from unbranched compounds (1, 4 ) should prove helpful in some doubtful identifications. Data on the original compound from other sources-e.g., infrared and ultraviolet spectra, gas chromatograms, method of isolation-will aid in identifications. The rate of flow of sweep gas did not appear t o be critical in our studies, but it must be constant to obtain reliable retention times. Injecting knowns periodically will detect changes in flow rate and other minor changes that may occur, and permit appropriate corrections to be made. Injection of 0.02 p1.-(about 20 pg.)of compound frequently caused more
than full-scale deflection. This amount was injected routinely because it was the least that the author could introduce without diluting the sample and masking part of the pattern with the solvent. When compounds give a weak signal, patterns may be improved by injecting as much as 50 fig, I n this study a 10-mv. recorder was used and the electrometer attenuator was set a t 4. By using a 1-mv. recorder and setting the attenuator a t 1, the sensitivity can be increased 40 times. (Base-line stability has been excellent.) Analyses on submicrogram amounts is therefore within the range of the method. Some of the analyses may be made quantitative but, in general, the procedure does not lend itself to quantification. Compounds that are easily converted to hydrocarbons give a much greater response than those difficult to convert, as evidenced by dragging of peaks. Acids, which resist conversion, appear in small amount. Knowing that the more polar compounds give less product is useful information in elucidating the structure of compounds. However, the presence of two highly polar groups may cause the response to be too weak to register on the recorder. The high-speed hydrogenation of the compounds is undoubtedly due to the small amount of the injected compound us. the comparatively large amount of catalyst, and the fact that the compound in its vapor state is available for contact with the catalyst. The apparatus provides a convenient means of studying high-speed hydrogenation and hydrogenolysis reactions. Attention has been directed thus far only to the main products. A study of the minor products-or, more precisely, fragments-undoubtedly will shed additional light on the structure of compounds, because neighboring groups do facilitate or hinder the cleavage of molecules a t specific points. Results
may be expected to reflect every nuance in structural variation. Findings with model compounds will be helpful in interpreting uncertain results until enough data to justify generalizations are accumulated. ACKNOWLEDGMENT
The assistance of Rafael Sarmiento, of the Entomology Research Division, Agricultural Research Service, U. S. Department of Agriculture, is gratefully acknowledged. LITERATURE CITED
( 1 ) Brenner, N., Coates, V. J., Nature 181, 1401 (1958). (2) Thompson, C. J., Coleman, H. J.,
Hopkins, R. L., Ward, C. C., Rall, H. T., ANAL.CHEM.32, 176%-5 (1960). (3) Thompson, C. J., Coleman, H. J., Ward, C. C., Rall, H. T., Zbid., 32, 424-30 (1960); 34, 151-6 (196%). (4) Whitham, B. T., Nature 182, 392
(1958).
RECEIVEDfor review July 30, 1962. Accepted October 17, 1962. Mention of proprietary products does not necessarily imply endorsement by the U.S. Department of Agriculture. Patent application has been filed for the apparatus.
Correction Reactivity of Some Hydroxyketones with Blue Tetrazolium I n this article by Peter E. Manni and Joseph E. Sinsheimer [ANAL.CHEM. 33, 1900 (19Sl)l absorbance values presented for cortisone acetate in Figure 4 should be multiplied by 10.
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