a good estimate of the actual gain and not just of Tm. Equivalent results were obtained over a wide spectral region, even when we used a modulated hollow cathode and lock-in amplifier to make photocurrent measurements. This apparatus and photon counting equipment could be used to evaluate the collection efficiency as previously described (8, 14). From Equations 2 and 3, the ratio of the product of the photocathodic current (measured in the PT configuration) and the charge of an electron to the photoanodic pulse rate (measured in the P M T configuration) is pIA1. By extrapolation, the photoanodic pulse rate a t A1 = 1 can be estimated so that the ratio yields p directly.
(12) RCA-1P28 Specification Sheet. (13) R. M. Schaffer, RCA, personal communication. (14) L. Birenbaum and D. B. Scarl, Appl. Opt., 12, 519 (1973).
RECEIVEDfor review May 2, 1975. Accepted July 7, 1975. Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this Research.
ADDENDUM
ACKNOWLEDGMENT We thank Steve Hoyt for machining the P M T housing.
LITERATURE CITED (1) J. D. Ingle, Jr., and S. R. Crouch, Anal. Chem., 44, 785 (1972). (2) RCA Photomultiplier Manual, Technical Series PT-61, RCA Electronic Components, Harrison, N.J., 1970. (3) EM1 Photomultiplier Tubes, Brochure 30M/6-67 (PMT), Gencom Division, Varian/EMI, Plainview, N.Y. (4) R. L. Klobuchar, J. J. Ahumada, J. V. Michael, and P. J. Karol, Rev. Sci. hstrum., 45, 1071 (1974). (5) R. Foord, R. Jones, C. J. Oliver, and E. R. Pike, Appl. Opt., 8, 1975 11969). ---, (6) R. Foord, R . Jones, C. J. Oliver, and E. R. Pike, Appl. Opt., 10, 1683 (19711. (7) A. T. Young, Appl. Opt., 10, 1681 (1971). (8) A. T. Young and R. E. Schild, Appl. Opt., I O , 1668 (1971). Jr.. Anal. Chim. Acta.. 77. 71 (1975). 191 \., .I. -. E. Hawlev - ,and -~-J. D. Inole.,~ (10) L. D. Gthman. S. R. Crouch, and J. D. Ingle. Jr., Ana/. Chem., 47, 1226 (1975). (11) F. Robben, Appl. Opt., 10, 776(1971). \
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2072
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Carbon Black Adsorbates: Separation and Identification of a Carcinogen and Some Oxygenated Polyaromatics
While the paper by Avram Gold, Anal. Chem., 47, 1469 (1975), describing the identification of polycyclic aromatic hydrocarbons and oxygenated polycyclics adsorbed on carbon black was in press, a paper by L. Wallcave, D. L. Nagel, J. W. Smith, and R. D. Waniska, Enuiron. Sci. Technol., 9, 143 (1975), appeared in which one of the same polycyclics (cyclopenta[cd]pyrene)was identified. The Wallcave paper should be added as a reference. Both papers are in agreement on the physical-chemical properties of the compound; in addition, the Wallcave paper presents PMR data. Also, reference 10 should read: L. Wallcave, Environ. Sci. Technol., 3,948 (1969).
ANALYTICAL CHEMISTRY, VOL. 47, NO. 12, OCTOBER 1975
