NOTES
1972
0.10
002
t-
0 1 -4.5
I
-4.0
I
-3.5
I
-3.0
I
-2.5
I
I
-2.0
I
I
-1.5
-1.0
I
1
I
-0.5
Log apparent current density a./cm.z. Fig. 1.-Comparison of anodic hydro en overvoltages on a-Pd-H and Pt bielectrodes; in hygogen stirred solutions.
The anodic curves clearly show these differences for Pt and a-Pd-H. Further confirmation can be seen from other data.'S2 The fact that the hydrogen diffusing through the a-Pd-H bielectrode is not the cause of the 0.12 slope can be seen from anodic polarization curves on a simple Pd anode' and also from data* on atomic hydrogen overvoltage on the anode side of an a-Pd-H bielectrode in hydrogen-free solution. (7) 8. Schuldiner, G. W. Castellan and J. P. Hoare, J. Chem. Phys.. 28, 16 (1958). (8) S. Schuldiner, J . Electrochem. Sac., 106, 440 (1959).
T H E STATIONARY PHASE IN PAPER CHROMATOGRAPHY BY GEORGEH. STEWART AND HYUNQ KYUSHIN Department of Chemistry, University of Utah Received April 86,1969
The analysis of the partition coefficient a and the Rfvalue in paper chromatograms by the method of Consden, et
where A J A , is the ratio of the areas of cross-sections of the mobile and the stationary phase, may be corrected for the non-constant value of the concentration profile over the length of the solvent path.2 The method of assigning a value to A, requires close analysis and standardization before values of the partition coefficient may be interpreted in terms of solution theory. The ability to predict the partition Coefficient by static methods would facilitate the choice of suitable solvent systems for chromatographic problems. Two pieces of information are required : (1) the cross-sectional area (or volume per unit length) of the active stationary phase and (2) the nature of the solvent in that phase. The stationary phase may be subdivided into two distinct regions, adsorption sites and solution.2 (1) R. A. Consden, A. H. Gordon and A. J. P. Martin, Biochem. J . (London). 38, 224 (1944). (2) fi. Krulla, Z . physik. Chsm., 6 6 , 307 (1909). (3) D. P. Burma, A m i . Chem.. B5, 549 (19531, contains review of
earlier work.
Vol. 63
Partition chromatography refers to the exchange between the mobile solvent and the solution held within the cellulose fibers while adsorption chromatography deals with the bonding of solute molecules to adsorption sites (primarily hydrogen bonding to glucoside hydroxyls) on the glucoside chains. When water is the major solvent, only the strongest bases will displace it from hydrogen bonds with the cellulose4and allow adsorption to compete with the partition mechanism. The occurrence of adsorption in a partition chromatogram is often signaled by tailing or ghost spots. The analysis of adsorption kinetics and isotherms should give some insight into these questions. To this end the authors have determined rates of adsorption and adsorption isotherms for the system water and Whatman 3MM chromatographic paper. The rates of adsorption were determined on paper samples previously dried for 48 hours in vacuo over P 2 0 6 . Vapor pressures were achieved with sulfuric acid solutions.6 The rate curves (Fig. 1) indicate that adsorption is essentially complete after 24 hours. This gives a measure of the time of exposure of chromatographic papers to solvent vapors prior to use necessary to prevent waterlogging and double-fronting.6 The values used in the isotherms, however, were taken a t two weeks to allow more complete equilibration. The weight of solvent adsorbed per gram of paper, w,is a measure of the extent of the stationary phase and provides a measure of A , in the Consden formulation. The fact that Rf values of unity are reported precludes the inclusion of dead-end capillaries exterior of the individual fibers as part of the stationary phase. The occurrence of such pools of static solvent is best considered as constituting a streamline of zero velocity in the mobile phase. The subdivision of the adsorbed volume into a bound and a condensed phase can be made-from the adsorption isotherm of Smith' (@ = wb W' ln[l -P/P0]) which allows for the swelling of the fibers and the increase in available bound sites with the percentage of moisture imbibed. The slope of the Smith plot yields the number of multilayer sites, E', expressed as a weight fraction, and the intercept yields the number of bound sites, Wb, also expressed as a weight fraction. It is expected that the two quantities should be equivalent since multilayers can be formed only on water which is hydrogen bonded to the cellulosic hydroxyls. This conclusion led us to believe that the paper samples contained a residual 2% water after drying and this was confirmed by two further analyses. The isotherm below p / p o = 0.4 should be little influenced by swelling and the BET isotherm should be approached as p / p o approaches zero. Application of the residual moisture correction to the BET isotherm gives approximately the same number of bound sites as the Smith treatment (Table I). To check the predicted residual moisture, the (4) F. M. Arshid, C. H. Giles and 8. K. Jain, J. Chem. Soc., 559 (1956). (5) R. E. Wilson, I n $ Eng. Chem., 13, 326 (1921). (6) H. G. Cassidy, Fundamentals of Chromatography," Interscience Publ., Inc., New York, N. Y., 1957, p. 164 et 8eg. (7) 9. E. Smith, J . Am. Chsm. Soc., 69, 646 (1947).
r
.
c
NOTES
Nov., 1959 0.4
1973
~
”
P/p,=
1.000
A
-
D
i
80.3 a 6
3
-3 .L-’
B 0.2 -4 J B
0.684
-
kinetics of drying data8 (Fig. 2)’ were extrapolated to “bone dry.” analytically, and reasonable agreement with the isotherm analysis was obtained. TABLE I Bound sites@
Multilayer sites
Residual moisture
Smith 0.046oom 0.046 0.019 BET ,044 ... .019 Drying curw ...... ... ,018 a Reported as grains of water per gram of paper.
The success of these treatments tempts us to determine an average capillary size. The data 0.020 indicates that condensation occurs only on filled 0 10 20 30 40 bound sites and all available bound sites (exclusive Time, 1, hours. of new ones due to swelling) are filled above Fig. 2.-Residual moisture loss per gram of cellulose. EXp/po = 0.4. The ratio of total water to bound trapolated by wlost = wg (I - e - k l t ) , 100”. water should be the average number of multilayers: WT/Wb = 9. This gives an average pore 1 . 2 7 diameter of about 50 A. This may be compared with electron microscope studiesgwhich give values of the order of 40 A and with non-freezing moisture 0.8 I analyses1o which giye maximum values ranging from 100 to 300 A. The importance of these 0.6 L-LLvalues is that they suggest that the kinetics of 5 6 7 8 9 10 partitioning of large molecules must be governed PlPo. by diffusion through a very tight labyrinth of glucoside chains necessitating the breaking of Fig. 3.-Huggins‘s interaction parameter p as a function of relative humidity p/po, 25’. hydrogen bonds, similar to the diffusion of solvents into dry fibers.ll gested that polymer solution theory is applicable The analysis of the adsorption isotherm by the in this region.12 Consistent with the results of method of Smith fails a t p / p o values greater than Simha and Rowens, the authors find that the 0.9. This is due in part to the limit to swelling of Huggin’s interaction parameter p13 has a near the cellulose fibers and in part to the approach to constant value over the range p / p o equal to 0.5 to pure condensation energetics. It has been sug- 1.0 (Fig. 3). (8) P. H. Hermans, “Contributions to the Physics of Cellulose The variety of treatments necessary to explain Fibers,” Elsevier Pub. Co., Ino., Amsterdam, 1946,p . 206. the adsorption isotherm of cellulose tells of the (9) s. Asunmaa, Suenak Papperstidn., 67, 307 (1954); C. A . , 60, heterogeneity of the stationary phase. Martin’s 1299g (1956). ~
(10) F. C. Magne, H. J. Portas and H. Wakeman, J . A m . Chem. Soc., 69, 1896 (1947). (11) Ref. 8,p a g e 31.
2
(12) R. Simha and J. W. Rowen, J . -4m. Chem. S o c . , 70, 1063 (1948). (13) M. L. Huggins, Ann. N. Y.Acad. Sci., 43, l(1942).
NOTES
1974
s~ggestion‘~ that it can best be approximated by a solution of polyols is still the best characterization of its average behavior in view of the applicability of polymer solution theory. With a clear definition of the size of the stationary phase, through arguments like those above, investigation of this aspect of the problem can be made. The authors hope that this note will renew interest in some of the fundamental aspects of paper chromatography. This investigation was supported by a research grant, A-2402(Cl), from the National Institute of Health, Public Health Service. (14)A. J. P. Martin, Ann. Rev. Biochem., 19, 517 (1950).
X-RAY ANALYSES OF THE SOLID PHASES IN THE SYSTEM LiF-ThR BY L. A. HARRIS,G. D. WHITE Ceramic Laboratory, Metallurgy Division AND
I M+ S
S+ S M M+ M M W M
S M M M+ W+ M M W W+
W
R. E. THOMA
Vol. 63 TABLE I INDEXED POWDER PATTERN OF LisThF7 sin’ 0 sin2 e
Obsd. 0.0142 .0295 .0309 .0449 .0617 .0721 .0759 .0914 .lo90 .1233 ,1338 .1378 .1428 .1543 .1582 .1687 .1898 .1956 ,2048 ,2147
Calcd. hkl 0.0142 001 .0296 101 .0308 110 .0450 111 ,0616 200 .0722 102 ,0758 201 .0913 211
...
..
.1233 .1339 .1375 .1432 .1541 .1586 .1683 .1894 .1955 .2049 .2145
220 212 221 103 310 113 311 203 302 213 321
Reactor Chemistry Division, National Laboratory,‘ Oak Rdue, Tenn. Received April 86, I069
The phase equilibrium diagram for the system LiF-ThF4 has previously been determined a t this Laboratory by R. E. Thoma, et al., and shown to contain four distinct solid phases, none of which were observed to have polymorphic transformations, The reliability of these compound formulas has been established by the methods outlined in the phase equilibrium paper.2 The X-ray examination of the crystalline phases and the analyses of their structure is the concern of the following paper. Material Synthesis.-Solid-state synthesis of the four compounds was attempted in order to procure single-crystal specimens for positive structure identification and to obtain sufficient quantities of the individual phases for density determinations. Samples of powdered materials having the proper chemical compositions were thoroughly mixed, placed in nickel tubes, evacuated, sealed and positioned in a platinum-wound furnace. The samples were heated and held slightly below their melting temperatures for a period of ten days. Single crystals for LiaThF7 and LiThzFs were obtained in this manner; however, materials of sufficient purity for density measurements were attained only for LisThFl and Li7ThaFsl. Determinations of the phases formed by the above methods were based on the optical and X-ray examination of the cooled material. X-Ray Methods.-Debye-Scherrer films were taken of all four phases using a 114.6-mm. dia. camera and Cu KCY( X = 1.5418 8.)radiation. Rotation, Weissenberg and precession diffraction patterns for the single-crystal samples were obtained from the Metallurgy and Ceramics X-Ray Laboratory.
X-Ray Results Li3ThF7.-The data obtained from the DebyeScherrer film for LisThFv were indexed (Table I) and found to best fit a tetragonal unit cell whose lattice parameters are ,a0 = 6.206 f 0.006 A. and co = 6.470 f 0.002 A. and which contains two molecules with a calculated density p = 5.143 g./cc. The observed extinctions from the Weissenberg and precession photographs are compatible with space groups P4/nmm or P4/n. (1) Operated for the U.8. Atomio Energy Commission by the Union Carbide Corporation. (2) R. E. Thoma, H. Insley, B. S. Landau, H. A. Friedman and W. R. Grimes, “Phase Equilibria in the Fused Salt Systems LiF-ThF4NaF-1hF4,” presented at meeting of the Am. Chem. Soc., Chicago, Ill., September 1958
I WW-
WM+ WW W W W W W W WWW W
W W
WW+ WWW-
Obsd. 0.2271 .2473 .25lO .2571 .2615 .2663 .2772 .2819 .2892 .3087 .3195 ,3283 .3503 .3695 .3814 .3892 .4012 .4156 .4309 .4422 ,4623 .4741 .4943
Calcd. hkl 0.2272 004 .2466 400 .2511 223 .2571 322 .2610 401 .2665 303 .2774 330 .2819 312 .2884 204 .3082 420 .3187 412 ,3281 323 .3505 224 ,3704 105 .3813 314 .3898 413 .4007 610 .4149 511 .4320 215 .4420 432
...
..
.4738 .4937
404 305
Li.~ThiF,~.-The type compound designated M&Fal, where M represents an alkali atom and X a heavy atom such as uranium or thorium, has been observed by investigators of the fluoride phase equilibrium relationships a t this Laboratory.2-s In the system LiF-ThF4, a compound with the above chemical ratio was observed and determined to be optically uniaxial.2a A comparison of the Debye-Scherrer films for Li7UeF31 and Li7Th6Fal revealed both compounds to be isostructural. Single-crystal specimens of Li7U6Fnl which were available permitted the authors to determine the unit cell and probable space group of Li7Th6F31 by analogy. Table I1 presents the powder diffraction data for the Li7Th6FB1indexed with the help of the Weissenberg and precession photographs of Li7U6Fal. The compound has tetragonal symmetry with unit cell dimensions a0 = 15.10 i 0.002 A. and co = 6.60 I 0.02 A.; the calculated density is p = 4.387 g./cc., assuming two molecules per cell. The space group I4Ja was chosen on the basis of the systematic extinctions of reflections observed on the single-crystal photographs of Li7U6Fa1. TABLE I1 INDEXED POWDER PATTERN OF Li7TheFal I W+ 6 €4
S
SS SS M M W W M M+ S-
sin2 e hkl Calcd. Obsd. 0,0162 0.0162 101 ,0209 .a208 220 .0206 211 .0267 .0373 .0370 301 .0474 321 .0477 .0524 .0520 420 .0578 411 .0581 .Of348 202 .0650 .0752 222 .0755 .0787 ,0786 501 .OS93 .0890 521 .lo45 .lo40 620 .lo98 611 .1103 .1306 631 .1308 .1352 640 .1355
I
W W W
VW MS W M M W
M W
MW
W W
W+
sin2 e Obsd. Calcd. 0.1456 0.1458 .1480 ,1487 .1514 .1515 .1562 .1562 .1587 .1584 ,1664 .1668 .1722 .1730 .1826 .1829 .1876 ,1872 .1978 .1984 .2034 .2034 .2176 .2186 .2312 .2317 ,2346 .2348 .2390 .2394 .2416 ,2420 .2450 ,2453
hkl
303 602 721 323 622 800 651 811 660 523 831 004 822 921 633 662 851
c
