produce a new interest in the flame fluorescence methods since, as was first pointed out by Alkemade (14) and demonstrated by Winefordner and Vickers (15), they have striking potential advantages over atomic absorption spectroscopy. In this respect, it has always surprised me that workers in flame fluorescence have, in general, failed to exploit the fact that the fluorescence phenomenon provides its own monochromator. In the arrangement shown in Figure 7, for example, if the illuminating source is "pure," the only need to have any wavelength selection is to avoid excessive noise owing to radiation from the atomic vapour. I would also like to refer to our recent work on the development of atomic absorption and atomic fluorescence methods for the direct analysis of solids (16, 17). The sample is made the cathode of a low-pressure discharge, and the atomic vapour is produced by cathodic sputtering. The encouraging results obtained in the analysis of low-alloy steels have recently been published (17). In that paper we reported the difficulties encountered when the method was applied to the analysis of aluminumand zinc-base alloys. These difficul-
MODULATED ATOMIC SPECTRAL LAMP
ATOMIC FLUORESCENCE
SYNCHRONOUS DETECTION SYSTEM
OUTPUT SIGNAL
Figure 7. Schematic diagram of nondispersive atomic flame fluorescence spectrophotometer
New automatic polarimeters make it easier to measure optically active substances with great accuracy.
Perkin-Elmer's new Models 241 and 241 MC Polarimeters could be just what you need if you're faced with one or more of the following measurement problems with optically active substances: • Quantitative determinations • Characterization of pure substances • Study of kinetic reactions • End point determination of titrations • Detection for liquid chromatography • ORD measurements These instruments work on the highly-valued principle of the optical null balance. You'll find them faster, surer and more accurate than other instruments. They give you the rotation on a five place digital display with sign.
Four integration times: 1,5,20 and 50 sec. Plus a recorder readout unit with four cyclic ranges: ±0.05°, ±0.5°, ±5.0° and ±50.0°. Operation? Extremely simple and versatile. Just push a button. You get an automatic gain and balance control, test deflection in + and - directions, automatic lamp ignition. Like to know more about the Models 241 and 241 MC? Write to the Instrument Division, Perkin-Elmer Corporation, Main Avenue, Norwalk, Conn. 06856.
PERKIN-ELMER
CIRCLE 185 ON READER SERVICE CARD 706 A • ANALYTICAL CHEMISTRY, VOL. 46, NO. 8, JULY 1974
