1218
ANALYTICAL CHEMISTRY
N. J., for providing the analyzed samples of cocoa. powders used in this investigation. LITERATURE CITED
(1) Boie. Heirrich. Pham. Z ~ Q75,968 ., (1930).
(2) Cappelli,G.,Ann.chim. appt., 14,254 (1924).
(3) Cenotti, A., Anales a8m. pub. argentinn. 8 , 400 (1920). (4) Dekker. M. J., Rec. trau. chim.. 22,143 (1903). ( 5 ) Emery. W. O.,and Spencer, G. C., J . 7 d .Eng. Chem., 10, 605 (1918). (6) Holmes. K. E., Analyst. 7 5 , 457 (1950). (7) Humphries. E. C., 8th Ann. Rept. Cocoa Research, 7mp. Coll. Trop. Agi.. Trinzdad, 1938.36. (8) Ishler, N. H., Finucane, T. P., and Borker, Emanuel, ANAL.
CHEM.,20,1162 (1948). (9) Jalade, M., Ann.fals. etfmudes, 22,396 (1929).
(IO) Jones, Marie, and Thatcher. R. L., ANAL. CHEM.,23, 957 (1951). (11) Kay. J., and Haywood, P. J. C., Analyst, 71, 162 (1946). (12) Kunae, W. E., Z . anal. Chem., 33, 1 (1894). (13) Lowe, E. H.. Analysl, 73, 679 (1948). (14) Macdonald, J. A,, Ann. Rept. Cocoa Reseaxh, Imp. Coll. T ~ o P . Agr., Trinidad, 1936,43. (15) Martin, F., and Clergue, H., Ann. chim. anal.,24, 202 (1942). (16) Maupy, L., Analyst. 22, 191 (1897). (17) Moir, D. D., and Hinks. E., Ibid.,60, 439 (1935). (1s) Moores. R. G.. and Campbell, H. A,. ANAL. CHEM.,20, 40 (1948). (19) Parks,A. E., andParks, H.A., Analyst. 62,791 (1937). (20) Pritzker, J.. and Jungkuns, R.. Mill. Lebensm. H y g . . 34, 185 (1943). (21) Wadsorth, R. V.,Analyst, 46,32 (1921). R ~ c n v for ~ oreview Ootober 27, 1953.
Accepted Maroh 20. 1954.
Partial Resolution and Detection of Some Cations by Differential Diffusion MARVIN ANTELMAN Maranter Laboratories, Ventnor City,
N. J.
ANALYTICAL
sep,arat? have been accomplished by the apphcatlon of diffusion techniques. In these procedures chemical potential gradients produce differential migration by diffusion (4). Uranium-235 is separated from uranium-238 for atomic purposes by allowing volatilieed uranium hexafluoride t o diffuse in multistage apparatus. Gaseous mixtures may be determined by microeffusiometry ( 1 ) . Porphyrins (a), azo dyes (S), radioactive ions (7), and ordinary eations (5, 6) have bsen resolved in solution by diffusionprocedures. The migration processes usually are performed in porous or gelatinous media in order t o prevent mixing. This paper describes the resolution of various cations by radial differential diffusion taking place in a concentrated gel of gelatin under the influence of a chemical potential gradient. No electric current is applied in the procedure. EXPERIMENTAL PROCEDURE
A thick concentrated gel was prepared by softening 16 grams of C.P. gelatin in 50 ml. of cold water and then adding 150 ml. of boiling water. Distilled water always was used. The gelatin was Domed into watch glasses (1.5 em. deep a t the center) and
his. pipet to the approxirhate center of the plates.
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paper. If the gels are alloivcd to stay for scveral days, they will harden. In most cases the concentric rings are still present in the hardened gel. The procedure of selective diffusion originally was attempted on gels formed in test tubes but failed to give good results. DISCUSSION
This diffusion procedure serves to resolve cations partially. When a cation mixture is $laced centrally on a gelatin surface, each component migrates under the influence of the chemical concentrations or potential gradient. The zone of each component extends from the starting position to the leading boundary. Each cation contaminates the zone of every more slowly diffusing cation; therefore, only a small fraction of the fastest migrating ion can be separated from others. Cross contamination of two and three cations, respectively, is illustrated schematically in Figure 3.
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After B few minutes, the surfaces became dry, for the solutions had diffused through the gelatin. Developing reagents were added in a sufficient amount to cover the surface and to develop distinct cancentric rings. The developing may take from less than a minute to an hour depending on the type of cations and the developing agents. Same cornbinations of cations and developing reagents failed to give good results. RESULTS
Many cation combinations were tested and are listed in Tables
I and IS. The difference in color of the contaminated aones and their position 8ewe t o identify the cations present in the mixture. The photographs show two partial seprtrations. Fignre 1 illustrates the psrtisl resolution of mercury(1) and lesd(1Ij from the middle and out developed with potassium iodide, whereas Figure 2 is the separation of iron(ISI), copper(SS), and cobalt from the middle and out developed with potassium ferrocyanide. Potassium iodide is superior to the chromate as a developer for group I metals, Potassium ferrocyanide is superior t o sodium phosphate as a developer of iron(SSI), copper(II), and cobalt ione. Results of Elective diffusion procedures may he recorded conveniently in colored pencil or crayon on polar coordinate
Figure 1. Partial Resolution of Me, Developed with Potassium I
VOLUME
26,
Table I.
Colors and Ions Developer
HgNOl AgNOa H ~ N O , :A ~ N O ~ HgNOz Pb(NOa)n HgNOa: Pb(N0ah Pb(N03.. AgNOi Pb(NOd3, AgPvOs Bi(NOda, FeCli Pb(NOd3 Hq(NOd, B~(NO&.'F~CII CuSO
