activated, and the effects of time variations as arrived a t by Method B, 1. The parallelism between the curves of the two temperatures is striking. Although temperatures higher than 60" C. were tried, the process of water removal was too rapid for accurate grading of the silicic acid. Figure 4 depicts the relationship between temperature, time of exposure, and per cent of water lost from the silicic acid compared to activity grades. Data were obtained by weighingfthe adsorbent before and after each activation by Method B, 1. Activity grade I cannot be achieved a t 50' C. even after 8 hours or after 10 hours a t 60" C. Method B, 2 yielded the results shown in Figure 5. The rapid changes from one activity grade to another due to small changes in temperature make this method feasible only under the most accurately controlled temperatures. Ordinarily, most laboratory ovens are not likely to have such small variations in temperature and therefore this method cannot be recommended. DISCUSSION AND CONCLUSIONS
Previous publications dealing with the activation of silicic acid relied on the desiccating ability of anhydrous solvents (11, 16, 18) or the exposure of the adsorbent to increased temperature for various lengths of time (6, 17-19). However, in all cases the criteria of activity were dppendent upon the movement of a single dye down the column
as developed with different solvents (g), or the use of several unrelated compounds of widely separated polarities (10, 18, 19). In no case were these activity gradings related to anything else described in the literature, and therefore investigators have had to depend on a development of their own technique and criteria of activation for a particular select experiment in which a group of compounds were to be separated (4). By applying the nidely known Brockmann dyes to ascertain the absorbent activities of the silicic acid and obtaining parallel results, and by treating the silicic acid and entire chromatographic procedure throughout in a completely standardized fashion, a meaningful range of adsorption activities can now be reproduced anywhere. Furthermore, the repeated use of standardized column measurements, absorbent purity, and a single solvent developing mixture makes possible a complete comparison of activity grades by methods 8,B, 1, and B, 2. The choice of method will depend upon available laboratory facilities. Thus, silicic acid, already accepted as a relatively inert adsorbent and thus suitable for the chromatographic separation of the more delicate compounds, can now be further utilized on the basis of its wide range of controllable adsorbent properties. LITERATURE CITED
(I) Brockmann, H., Schodder, H., Ber. 74,
73 (1941).
(2) Cahnmann, H. J., ANAL. CHEM.29,
1307 (1957). (3) Coleman, G. H., Farnham, A. G., Miller, A., J . Am. Chem. SOC.64, 1501 (1942). (4)' Fillerup, P. L., Mead, J. F., Proc. SOC.Exptl.Biol. Med. 83, 574 (1953). (5) Howton, D. R., Science 121, 204 (1955). (6) Kay, L. M., Trueblood, K. Y., ANAL. CHEM.26,1566 (1954). (7) Lederer, E., Lederer, M., "Chromatography, p. 20, Elsevier, New York, 1957. (8) Ibid., p. 22. (9) Ibid., p. 24. (10) Le Rosen, A. I,., J . Am. Chem. SOC. 64. 1905 (1942). (11) )bid., 67, 1885 (1945). (12) Muller, P. B., Helv. Chim. Acta 26, 1945 (1943). (13) Noll, H., Bloch, H., Asselineau, J., Lederer, E., Biochim. et Biophys. Acta 20, 299 (1956). (14) Fy,R. L., Bickford, W.G., Dieckert, J. L\., ANAL.CHEM.316, 1447 (1959). (15) Reichstein, T., Schoppee, C. W., Discussions Faraday SOC.7, 305 (1949). (16) Schroeder, W.A., Ann. N . Y. Acad. Sci. 4 9 , 204 (1948). (17) Trappe, W.,Biochem. 2. 305, 150 11940'1. (18) Trueblood, K. Tu'., Malmberg. E. W., ANAL.CHEY.21, 10% (1949). (19) Trueblood, K. N., Malmberg, E. W., J . Am. Chem. SOC.72, 4112 (1950). RECEIVED for revien- August 24, 1960. Accepted December 7, 1960. Work was supported by Grants Yo. A-1078 and 8-1441 from the Iiational Institute of Arthritis and Metabolic Diseases of the Sational Institutes of Health, Bethesda, Md.; and Grant Xo. G-8406 of the Xational Science Foundation. Roger Hernandez and Raymond Hernandez, Jr., are undergraduate participants in research on the National Science Founda tion Grant No. G-8406.
The Rapid, Trace Analysis of Phosphate Mixtures by a Paper Chromatographic, Densitometric Procedure R. H. KOLLOFF Monsanfo Chemical Co., Si. louis 66, Mo.
b A high capacity chromatographic paper and modified solvent make possible the rapid and quantitative densitometric determination of as little as 0.02% Na4P207 in soluble orthophosphates. Complete hydrolysis of condensed phosphates on the chromatogram without paper deterioration and new, highly selective, chromatographic sprays are described. Results are also given on the extension of this technique to the analysis of soluble condensed phosphate mixtures and calcium phosphates.
A
recent developments have made ion exchange a precise and relatively rapid procedure for the analysis of commercial mixtures of condensed phosphates (9, I S ) , little has been reLTHOUGH
ported in the area of trace analysis of phosphate mixtures. An existing colorimetric procedure for the determination of trace amounts of pyrophosphate in orthophosphates is fast, extremely precise, and sensitive, but it is empirical in nature, lacks flexibility, and is designed primarily for use in routine control work (10). Paper chromatography is subject to fewer interferences than the above colorimetric procedure and is more flexible, but, to date, it has suffered from a lack of sensitivity and precision for minor constituents (
