1721
Anal. Chem. 1981, 53, 1721-1723
interval from 3 M HF/0.625 M HNOBto 21.6 M HF/1.5 M HNO,; and in Figure 4 from the mixture of hydrofloric acid and nitric acid 1:l between 2 M HF/1.25 M HNOB and 12 M HF/7.5 M "0,. The quoted values are the average of a minimum of two determinations. For an adsorption of 50% (log D F= 1.7) the relative standard deviation is *3%. The results in Figure 1 are in accordance with the data published by Faris for dynamic conditions (1). Only for palladium, platinum, gold, and mercury differing D values have been obtained, presumably due to dzferent experimental conditions. Rather unreproducible results were obtained for the adsorption of silver ,and antimony. These results are not given in detail. For niobium, the observed increase in D with increasing acid concentration can be attributed to the disappearance of oxyfluoro complexes. The comparison of results given in Figures 1-4 indicates that with increasing fraction of nitric acid there is a continous decrease of the D value of all elements tested. This can be explained by the formation of less charged and less adsorbable anionic species in the presence of nitric acid. These distribution data enable one to work out useful separation procedures. For instance, on their basis a rapid
separation procedure has been developed for the radiochemical neutron activation analysis of high-purity niobium involving short-lived indicator radionuclides (3).
LITERATURE CITED (1) Faris, J. P. Anal. Chem. 1960, 32, 520-522. (2) Faris, J. P. Anal. Chem. 1064, 36, 1157-1158. (3) Faix, W. G.; Caietka, R.; Krivan, V. Anal. Chem. 1981, 53, 1594- 1598.
Werner G. Faix Rostislav Calet ka Viliam Krivan* Sektion Analytik und Hochstreinigung Universitat Ulm Oberer Eselsberg N26, D-7900 Ulm Federal Republic of Germany RECEIVED for review March 24,1981. Accepted May 26,1981. This project was financially supported by Bundesministerium fur Forschung und Technologie, Bonn. Irradiation facilities for the production of radionuclides were provided by Kernforschungszentrum Karlsruhe.
Comments on Noise and Digital Resolution in a Microprocessor-Controlled Spectrophotometer Sir; We would like to a.dd to the paper by Kaye and Barber ( I ) . They made the remark that surprisingly they found the temperature coefficient of the photomultipliers was somewhat less than the figure given by the manufacturer, Hamamatsu Corp. This is not especially surprising to us. The main reason being that all of our data are taken from large samplings and in general indicate a worse case situation. That is true not only for temperature coefficientsbut also for spectral response curves. In actuality, there is a resonable variance tube to tube, since the cathodes of photomultiplier tubes tend to be both interference filters and plhoto emissive devices. Each layer of the film tends to be quite thin and not precisely controlled in thickness. In recent years we have found a tendency for the detectors to become more and more uniform. This is probably the result of better control over the materials used in making the tube, plus a better environment within our factory situation. But, the user and especially the design engineer should take note
of the fact that the data shown in detector manufacturer's catalogs is statistical in nature and does not represent any particular tube. For this reason, for many years Hamamatsu has taken a very strong negative stand utilizing photomultiplier tubes as standards over a long period of time. Applications such as the one described by Kaye, which rely on relatively short term stability are within the state of the art.
LITERATURE CITED (I) Kaye, Wibur; Barber, Duane Anal. Chem. 1981, 53, 366-369.
R. Eno Hamamatsu Corporation 420 South A~~~~~ Middlesex, N~~ jersey 08846 RECEIVED for review March 4,1981. Accepted April 10,1981.
AIDS FOR ANALYTICAL CHEMISTS Colorimetric Measurements in a Liquid Scintillation Counter Martin W. Heitzmann" sind Leonard A. Ford Division of Drug Chemistty, Food and Drug Administration, Washington, D.C. 20204
The concept of making high-precision photometric measurements by using a radiosotopic light source was first reported by Ross ( I ) . The instrument used in his experiments was a hybrid constructed from portions of a liquid scintillation counter (LSC), a multichannel pulse height analyzer, and a
custom-made sample chamber containing standard 1-cm cuvettes for the light source and sample holder. In an earlier paper (21, Ross described the use of an isolated internal standard cell to distinguish between the contributions of chemical and color quenching to total quenching. By se-
This article not subject to U S . Copyright. Published 1981 by the American Chemical Society
