should have general applicability in those cases where it is desired to have a certain amount of a high boiling solvent residing on the column and still be able t o operate at high sensitivity levels where, under ordinary conditions, the solvent excessive noise inbleed would enterthe detector and terference. In particular, this method should allow isomeric separations on AgN03 columns containing benzyl cyanide to have very good resolutions at high sensitivities since enough benzyl cyanide can be added to aid in the separation and yet not interfere with the signal reaching the detector unit.
LITERATURE CITED F, Armitage, J, chfomatogf,, *, 655 (1959), (2) B. W. Bradford, D. Harvey, and D. E. Chalkley,J. Inst. Pet., London, 41,80 (1955).
(3) M. E.
Bednas and D. s. Russell, Can. J. Chem., 3% 1272 (1958).
RECEIVEDfor review January 15, 1976. Accepted May 10, 1976. This work was supported by the Energy Research and Development Administration.
Instrument Calibration for the Mass Chromatograph Robert J. Lloyd, David E. Henderson, and Peter C. Uden” Department of Chemistry, University of Massachusetts, Amherst, Mass. 0 1002
The mass chromatograph (I-3), a dual gas density detector gas chromatograph designed for on-the-fly molecular weight determination, is based on the fundamental concepts of numerous workers (4-9). Samples are split into two approximately equal fractions after volatilization in the injection port, are trapped on identical traps, and then simultaneously backflushed onto two matched columns, two different carrier gases being employed. Theoretical discussions (3,I O ) indicate that the value of the molecular weight (M,) of a n unknown compound is given by Equation 1
where A1/A2 is the ratio of the compound’s response in de~ McG:!are the molecular weights of tectors l and 2, M C Gand the carrier gases and K is an instrumental calibration factor. K must be determined initially from known compounds using Equation 2.
There are three distinct regions of the calibration curve of the K factor vs. molecular weight of the standard compound ( M W s t ) ;Le., where M W s t < M W C G I ,M W C G < ~ MWst < M W C G ~and , M W C G
