Over a wide range of pressures. Other compounds, such as serum proteins, give better resolution at lower pressures. LITERATURE CITED
( 1 ) Bailey,
S. W.,Hackman, R. H., J .
Chromatog. 8, 52 (1962). ( 2 ) Flynn, F. V., De Mayo, P., Lancet 261, 235 (1951).
( 3 ) Foster, A. B., Newton-Hesrn, P. A,, 1956, p. 30. Stacey, ( 4 ) Hollinger, N. F., Lansing, R. K., J. Chromatog. 5 , 38 (1961). ( 5 ) McDonald, H. J., “Ionography,” Year Book Publ., Inc., Chicago, 1955. ( 6 ) Pacsu, E., Mora, T. P., Kent, P. W., Science 110, 446 (1949). ( 7 ) Ribeiro, 1,. P., Mitidieri, E., hffonso, 0.R., “Paper Electrophoresis,” Elsevier, Amsterdam, 1961. M.j
(8) Smith, I., “Chromatographic and
Electrophoretic Techniques,” T’ol. 1 , 2nd ed., p. 250, William Heinemann, London, 1960. ( 9 ) Ibid., Vol. 2, p. 11, William Heinemann, London, 1960. (10) Walpole, G. S.,J . Chem. SOC. 105, 2501 (1914).
RECEIVED for review November 22, 1963. Accepted January 27, 1964.
Separation of Various Cations by Reversed-Phase Partition Chromatography Using Neutral Organophosphorus Compounds JEROME W. O’LAUGHLIN and CHARLES V. BANKS lnstitufe for Atomic Research and Department o f Chemistry, Iowa State University, Ames, Iowa
b The use of the neutral organophosphorus compoun ds tri-n-butylphosphate (TBP), tri-n-octylphosphine oxide (TOPO), and bis(di-n-hexylphosphiny1)methane (HDPM) as stationary phases in the reversed-phase partition chromatography of various metal chlorides, nitrates, and perchlorates was investigated. RI and R, values are reported as a function of the acid concentration of the mobile phase for the movement of a large number of cations on paper impregnated with TBP, TOPO, or HDPM. Elution curves are also given for several alkali metal and alkaline earth perchlorates on columns packed with Kel-F treated with these three extractants.
R
PARTITION chromatography is a very useful technique for the separation of various cations. This technique is closely related to liquid-liquid extraction except that the water-insoluble extractant is immobilized on some stationary] inert support. The reversed-phase description arises because of the convention, especially in paper chromatography, of regarding the organic phase as the mobile phase. Fidelis and Siekierski (’7) reported the separation of the lighter rare earths on columns of kieselguhr impregnated with TBP, using 15.1 to 15.8X nitric acid as the mobile phase. I n a later paper (8) these authors extended this work to the heavier rare earths which are normally more difficult to separate. They obtained fair separations using 11.5M , 12.3J1, 13.0X nitric and concentrated hydrochloric acid as the mobile phases. Gw6idi and Siekierski (11) reported the separation of various oxidation states of plutonium using this technique and Siekierski and Sochaka (27) reported the separation of calcium and scandium EVERSED-PHASE
1222
ANALYTICAL CHEMISTRY
on T B P columns using 6M hydrochloric acid as the mobile phase. Mikulski and Stroliski (60) gave a separation of zinc, manganese, and cobalt from iron on a T B P column and in another paper (21) describe the separation of tin(I1) and tin(1V) and of tin, tellurium] and antimony. Small (28) incorporated T B P into a cross-linked copolymer of styrene and divinylbenzene to give a material having useful properties as a column packing and he called this technique “gel liquid extraction” or GLX. He presented elution curves showing the separation of uranium and thorium, yttrium and thorium, and iron and yttrium nitrates, and in a later paper (69) showed the elution curves for rare earth nitrate mixtures. Pierce and Peck (24, 26) investigated the separation of the rare earths on columns packed with a polyvinyl chloride-polyvinyl acetate copolymer impregnated with di(2-ethylhexyl)orthophosphoric acid (HDEHP) using gradient elution with perchloric acid. Cerrai and others (6] 4, 6) also studied the separation of the rare earths on cellulose columns and paper treated with H D E H P using hydrochloric acid as the mobile phase. Testa (SO) reported the separation of a number of cations on paper treated with tri-n-octylamine. He reported the separation of zirconium and hafnium among other interesting separations. Cerrai and Testa also reported a number of separations using cellulose (1) and Kel-F (3) impregnated with TOPO as the column packing. Several different authors (9, 12, 25) have recently reported the use of a Kel-F column impregnated with T B P for the separation of uranium from a variety of other elements. Dietrich (6) described the use of a column packed with glass beads coated
with T O P 0 to remove uranium from urine. Winchester (52) used an alumina column impregnated with H D E H P to separate rare-earth mixtures. Fritz and Hedrick (10) described the separation of iron(II1) on columns packed with Haloport-F impregnated with 2-oc tanone. I n this report the recently synthesized extractant, bis(di-n-hexylphosphiny1)methane or H D P M (M), is compared with T B P and TOPO as the stationary phase in reversed-phase partition chromatography. Data on the movement of a number of metal chlorides, nitrates] and perchlorates as a function of the acid concentration of the mobile phase are presented using both paper and column chromatography. EXPERIMENTAL
Apparatus and Reagents. Schleicher and Schuell, KO.589 paper was used throughout this investigation. Disk chromatograms were run on Blue or Red Ribbon paper and sheet chromatograms on Blue or Orange Ribbon paper (58 X 58 cm.). The sheet chromatograms were developed in a “Chromatocab” (Research Specialties Co., Richmond] Calif.). Disk chromatograms were developed in Petri dishes. Kel-F, a fluorocarbon polymer, was obtained from the Minnesota hlining and Manufacturing Co. (hlolding Powder Grade 3010 or 300). This resin was a mixture of particle sizes and the 60-80 mesh fraction was used in this work. A typical column equipped with a floa-type conductivity cell for monitoring the effluent (when water was used as the mobile phase) is illustrated in Figure 1. The cell was used in conjunction with a Wheatstone bridge using a Leeds & Northrup KO. 1553 Ratio Box and associated equipment recommended in its bulletin DB-1199. Any unbalance signal from the bridge
/I,
TO R E S E M R
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(1000 cycles per secclnd) was amplified and fed into a Mosel). Type +I-1AC-DC converter. The L)C signal from the converter was monitored with a Sargent Model M R recorder. I n cases where the eluent was not water, fractions of the effluent were analyzed by flame photometry using a .Beckman Model B spectrophotometer fit'ted with a Beckman flame attachment. The lanthanide, zirconium, and hafnium salts used were Xmes Laboratory stock. T B P was a Fisher Scientific Co. "purified" chemical. TOPO was an Eastman Organic IChemicals product. HDPM was synthesized in the laboratory (26). Paper Chromatography. The general techniques of paper chromatography are adequately treated in a number of text's and particularly well by Karel Macek in Chapter 7 of "Chrornato raphy" edited by Erich Heftrnann $14). Any important diferences in the techniques used in this investigation from those given by Macek will be noted The paper was imnregnated with the organophosphorus extractant before use by soaking t,he paper in a carbon tetrachloride solution of TBP, TOPO, or HDPM (20% by volume, 0.2M or 0.1Ji, respectively, unless otherwise noted) and allowing the carbon tetrachloride to evaporate. The reason that the papers were impregnated with different amounts of the three extractants was so that, the R , values would be other t,han 1 or 0 in as many cases as possible. The treated paperr: were spotted with 1-A amounts of a 0.1M solution of the appropriate salt of the metal to be studied and then developed. Disk chromatograms were developed to within 2 to 3 em. of the edges (20 to 60 minutes depending on the size of the wick) and the sheet chromatograms were developed for about 12 hours using the ascending technique. The locations of the various cations after development mere determined by
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VOL. 36, NO. 7 , JUNE 1964
1223
spraying with a n alcoholic solution of 8-quinolinol and then exposing the paper to fumes of ammonia. A lecture size cylinder of ammonia was very convenient for the latter purpose. Almost all the cations could be detected either by their fluorescence under ultraviolet light or as dark spots on a faintly fluorescent background. A 0.1% aqueous solution of Arsenazo (13) was somewhat more convenient for the detection of the heavy metals such as thorium, uranium, and the lanthanides. These elements are readily detected as blue zones on a pink background after spraying with Arsenazo and treating with ammonia. Sodium and lithium were detected by their fluorescence after spraying with zinc uranyl acetate and acetic acid. Column Chromatography. Columns, similar to the one illustrated in Figure 1, were packed with Kel-F impregnated with H D P M , TOPO, or T B P . The Kel-F was prepared by making a slurry of two parts Kel-F to one part by weight of H D P M or TOPO in carbon tetrachloride a n d allowing the carbon tetrachloride to evaporate while stirring continuously. After complete removal of the carbon tetrachloride the resulting product was a free-flowing white powder. The colunins were packed with the dry powder and water slowly forced through the column from the bottom in order to prevent formation of air bubbles. The column was not allowed to go dry. I n the case of T B P the column was first packed with Kel-F and a solution of one part T B P to two parts chloroform passed through the column. The column was air dried until no odor of chloroform could be detected. The column was then treated as the H D P M and TOPO columns. I n cases where the conductivity method was not used for monitoring the effluent the conductivity cell was removed. The sample solution was added with a microsyringe through the gum rubber section a t the top of the column (Figure 1) without interrupting the flow of the eluent through the column. The eluent was forced through the column by maintaining a slight positive head of air pressure over the eluent in the reservoir. The pressure, and hence the flow rate, was controlled by a Johnson air regulator. RESULTS A N D DISCUSSION
Movement of Metal Nitrates as Function of Acid Concentration. The movement of various metal nitrates on papers impregnated with T B P , TOPO, and H D P M are shown in Table I. The papers were developed (with t h e grain of t h e paper) for 14 hours using ascending chromatography. The alkali and alkaline earth nitrates are not appreciably extracted from acidic solutions by T B P or TOPO (31) and as expected the R, values were one with 0.5, 3, and 6.11 nitric acid. This waq also the case with H D P M as the stationary phase. It was somewhat 1224
ANALYTICAL CHEMISTRY
Table 11.
R, Values for Three Lanthanide Nitrates on TBP-Treated Papers
% TBP Element La Tb
Lu La
Tb Lu La Tb Lu
HIYO,, Af
1
15.7 15.7 15.7 12 12 12 9 9 9
1.0 0.71 0.57 1 .o 0.93 0 83 1 0 1 0 1 0
5 1. 0 0.67 0.33 1.0 0.83 0 67 1 0 0 86 0 72
difficult to detect these metals after development with acid more concentrated than 6M and it was initially assumed the Rf values remained one. With concentrated nitric acid as the mobile phase, barium is strongly retained on treated or untreated paper but this is merely due to the insolubility of barium nitrate in concentrated nitric acid. No appreciable retention of chromium(III), nickel, copper, zinc, cadmium, or lead was noted in agreement with known partition data for T B P and TOPO. -4lthough iron(II1) is not reported to be extracted from nitric acid media by TOPO (31) it is significantly retained on the TOPO-treated papers, and somewhat by T B P from 6 X acid and is held a t the start line on the HDPM-treated paper up to 1 2 N acid. Bismuth is retained somewhat by all three extractants and in agreement with partition data shows its lowest R, (highest partition coefficient) with the most dilute acid. Aluminum was retained to some extent on the H D P M paper but tailed badly probably because of slow kin;tics in the partition equilibria. The lanthanides, scandium, yttrium, uranium(VI), zirconium, and thorium show similar behavior. A411were held progressively tighter by TBP, TOPO, and H D P M in that order. All show a minimal Rf value on the T B P papers around 6M acid and show steadily increasing Rf values on the TOPO and H D P M papers. The minimum in a plot of R, values or maximum in a plot of the partition coefficients as a function of acid concentration is expected on the basis of a competitive extraction of nitric acid and the metal nitrates (62, 6.9). This was predicted for the extraction of uranium(V1) with T B P a t 4 M nitric acid. It should be noted, however, that Hesford, Jackson, and McKay (16) found that the partition coefficients for the extraction of the lanthanides into 100% T B P increased monotonically with nitric acid concentration. Also the column data of Fidelis and Siekierski ( 7 , 8) indicate that the lanthanide nitrates are held progressively tighter as the nitric acid concentration is increased. The movement of lanthanum.
10 1.0 0.53 0.20 1.0 0.75 0.5 1 0 0 90 0 72
20 1.0 0.52 0.28 1.0 0.6 0 35 i n
0 86 0 66
50 1.0 0.35 0.13 1.0 0.6 0 25 i n
0
75
0 50
terbium, and lutetium nitrates was rechecked using radial chromatography. The results, Table 11, are in agreement with those of the above workers ( 7 , 8, 1b). No definite reason can be given for the difference in the behavior of these lanthanide nitrates by the ascending and radial methods. The TBP-treated papers greatly hindered the flow of solvent, however, and the solvent front advanced such a short distance and so irregularly using the former method that accurate determination of R, values was impossible. The sharper zones obtained using radial chromatography were mwe easily located and these results are considered to be more significant. Also the possibility that the T B P partially decomposed during the much longer development time required by the ascending method cannot be overlooked. Movement of Metal Chlorides a s Fimction of Acid Concentration. The movement of various metal chlorides on papers (Blue Ribbon), developed the same as described in the previous section, is shown in Table 111. Exceptions are the papers impregnated with T B P and used for the 6M and 12M runs where a 0.2-If T B P solution in carbon tetrachloride was used to impregnate the paper. Recently Ishimori and others (16, 17) have compiled the known data on the extraction of the metallic elements into T B P and TOPO solutions. They compared these data with data from Kraus on the adsorption of metal chlorides on anion exchange columns. The data on the Rf values agree well with the data given by Ishimori. As expected, large partition coefficients result in low R f values. The R, values for the alkali and alkaline earth metals appeared to be one and are not given in the tables. The alkaline earth chlorides are retained somewhat with concentrated hydrochloric acid, but, as in the case of barium nitrate with concentrated nitric acid, this is not due to the extractant. The same retention is observed on untreated papers. It is of interest that in the case of scandium, yttrium, and lanthanum as well as with zirconium, hafnium, and thorium the lighter member of each set
has the lowest R, value (highest partition coefficient) and the R, value increases as atomic number increases. An increase in R, (decrease in partition coefficient) is not appment in the series zinc, cadmium, and niercury(I1) nor is any decrease in the partition coefficients of the alkali and alkaline earths reported with increasing atomic number (16). Iron is also strongly retained a t higher acid concentrations. I t is tempting to postulate that these latter metals are extracted as the chloride complexes but White (31) reported that this is not the case with the iron-TOP0 system and that the evidence is not in faror of the adduct being HFeC14.2TOPO. Katain (18) reported that the species in the organic phase for the extrartion of trivalent metal chlorides with many organic solvents was the neutral species HMCl,. He also noted, hoYvever, the TAP seemed to coordinate differently than the normal organic :,olvents and, like the halide ions, was capable of calling forth lower coordinat Lon numbers of its partner cations than they might normally show. I t would be expected that this would also be true for TOPO and H D P M . The above suggests that with normal organic solvents the extraction of the chlorides may be thought of as involving the replacement of waters of hydration around the cations by halide ions. At high acid concentrations the activity of water is lowered and the formation of a neutral species, HMC14, takes place in which the metal shows a lower coordination number. The organophosphorus extractants, hoNever, seem capable of replacing waters of hydration even a t low acidities [Note the low R f values for Fe(II1) with TOPO and H D P M in 0.5121 acid]. The species extracted by TOPO is reported to be FeC13.2TOP0
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The more highly charged cations are more extensively hydrated in aqueous solution and the waters of hydration should be even more difficult to replace. I t is interesting that H D P M retains the rare earths, yttrium, scandium, and the quaclrivalent elements better than TOPO or T B P while TOPO seems slightly superior for zinc, cadmium, and mercury as well as cobalt, copper, gallium, indi um, and possibly iron(II1). I t should be kept in mind, of course, that the T O P 0 concentration on the papers is twice as great as H D P M . For the same amounts of the three extractants on the paper, the R, values for any given metal are progressively lower for TBP, TOPO, and H D P M in that order. The relekive differences in the two groups of metals still exist, however. Movement of Metal Perchlorates as a Function of Acid Concentration. The movement of a number of metal VOL. 36, NO. 7, JUNE 1964
1225
Table IV.
Rf Values for Metal Perchlorates on TBP-, TOPO-, and HDPM-Treated Papers 3 . OM HCIO,
0 . 5 M HCIO,
Element Be Zn Cd
3 In
TXI) Pb(I1) Mn Fe( 111) co
Ni
cu
UVI Th Y
sc
Ce(II1) Ltt
Tb Gd Tm Lu
TBP
TOPO
HDPM
TBP
TOPO
HDPM
1 .o 0.78 0.90 0.51 1.0 0.89 0 0.64 0.94 0.93 0.94 0.94 0.93 0.71 0.95 0.95 0.77 0.92 0.91 0.90 0.90 0.89 0.89
1.0 1. o 1.0 0 . 70 1.0 0.11 0 0.82 1.0
0.32O 0.72 0.06 0.59 0 0 0.14 0.04
1.0 1 .o 0.88 0.66 1.0 0.79 0 0.44 1.0
0 . 34a 0.92 0.86 0.69 1.oa 0 0 0.38 0.84
i.0 1.0 1.0 0 0.10 1.0 0 1.0 1.0 1.0 1.0 1.0 I .o
0.92 1.0 0.87 0 0 0 0 0 0 0 0 0 0
1.0 1.0 1.0 0.64 1.0 0.88 0 0.44 1.0 0.94 1.0 1.0 1.0 0.41 0.83 1.0 0.27 1.0 1.0
L O G
n
n
Acid front 0>92 1.0 a Tailed, in case of AI from R/
=
0.97 0 to 1.
n nB n 02 0 46 0 08 0 09 La 0 46 0 37 Ce 0 47 0 25 Pr 0 47 0 23 0 13 Xd 0.45 0.23 0.13 Sm 0 36 0 13 0 13 Eu 0 38 0 14 0 11 Gd 0 43 0 16 0 11 Tb 0 36 0 09 0 11 0 36 0 08 0 08 0 40 0 07 0 07 Er 0 38 0 06 0 10 Tm 0 37 0 05 0 08 Yb 0 30 0 04 0 05 Lu 0 28 0 05 0.04 U(VI) 0 0 0 Th 0 0 0 02 a S and S glass fiber paper No. 26 used for 9M HC10,. 0
Y
i:
Table VI.
Element Li Na Mg
Ca
Sr
Ba Mn co Ni cu Zn Cd Hg
1.0 1.0 1.0 1.0
1.0
1.0
i.0
Rf Values for Metal Perchlorates on HDPM-Treated Paper Descending Ascending HpO 0.05M HClO4 Hz0 0 . 1 M HC104 1 1
I
0.14 0.05 0.24 0.30 0.03 0.12 0.18
0.67 0.82 0.10 0.01 0.37 0.37 0.01 0.05 0.19
...
...
...
... 0.02 0.01
0.05 0.02
;:I)
Ce(1II)
I:( VI) Acid front 1226
?a
0.93 1.0 0.87 0 0 0 0 0 0 0 0 0 0
perchlorates on TBP-, TOPO-, and HDPM-treated papers (Blue Ribbon) is shown in Table IV. The R , values show t h a t almost all the metal perchlorates are more strongly retained on the H D P M paper than on the T B P or TOPO papers. The most striking difference noted is the behavior of the lanthanides which all have R, values of zero with HDPM, are slightly held by T B P and not a t all by TOPO. Scandium is held better by TOPO than T B P a t 0.5M and 3M acid but its R, value decreases with increasing acid concentration for T B P and increases slightly for TOPO. It is strongly held by HDPM. Iron and aluminum tailed badly and R, values for these elements are not too significant. The R/ values for cadmium and manganese increased rapidly with increasing acid concentration on the H D P M paper while the R j values for
Table V. R, Values for the Lanthanides, Scandium, Yttrium, Uranium, and Thorium on HDPM-Treated Paper" Element 9M 9M 9M HCI HIiOa HC1Oda SC
?a
1 .o 1.0 1.0 0.06 0.23 1.0 0.04 1 .o 1.0 1 0 1 0 1 0 1 0
...
0.37
ANALYTICAL CHEMISTRY
I 1 0.14 0.07 0.29 0.32 0.03 0.11 0.20 0.12 0.11 ...
0.04 0 0.05 0 0
1
1 0.24 0.04 0.85 0.85 0 0.11 0.54 0.14 0.07 ... 0.01 0 0 0
0 0.85
zinc and lead increase somewhat less rapidly. The lanthanides, scandium, yttrium, uranium, and thorium were chromatographed on glass fiber paper impregnated with H D P M ( 0 . M H D P M in carbon tetrachloride) using 9-If perchloric acid as the developing agent. Ordinary paper was not satisfactory. The glass fiber paper was soaked in aqueous ammonia after development which neutralized the excess perchloric acid and precipitated the lanthanideb on the paper. The paper was then sprayed with Arsenazo and all the zones except for lanthanum and cerium could be found. The results are shown in Table V and rompared with R, values for these elements with 9 J I nitric and hydrochloric acids. The movement af the alkali, alkaline earth, and several other metal perchlorates on HDPM-treated paper with water and rather dilute (0.05N and 0.lM) perchloric acid was btudied. The R, values obtained are presented in Table VI. h number of separations of metal perchlorates were possible using radial chromatography which would not be evident from the sheet results. Sodium and lithium could be nicely separated for example, on filter paper disks impregnated with HDPAI. The alkaline earths could also be separated by this technique. The R, values for sodium and lithium both when spotted separately and as a mixture are shown in Table VII. The alkaline earth and aluminum perchlorates were chromatographed using the radial technique and the results are given in Table VIII. The zones were sharply separated but when barium was present the strontium and barium zones overlapped. The displacement of strontium and barium by 0.1X perchloric acid permits an exceedingly sharp separation of these two elements from the remaining members of the group. All of the strontium and barium is displaced by 0.1.M perchloric acid and the trailing edge is very sharp. Provided the capacity of
Table VII. R, Values for Sodium and Lithium Perchlorates on HDPM-Treated Papers on Development with Water (Blue-Ribbon paper) R, -Run Li Na 1 2 3 4 5"
0 50 0 63 0 63
0 83 0 75 0 84
Be, Mg, Ca, Sr, Ba, and AI perchlorates were also present. They all had smaller Rr values.
Table VIII. R, Values for Alkaline Earth Perchlorates Spotted Separately and in Mixtures (Solvent, 0.1M HClOa; Red Ribbon paper)
R, values
Run 1 2 3 4
5 6 7
Lo
Ce
Figure 2.
Pr
Nd
Rf values for
I
I
I
Sm
Eu
Gd
I Tb
I Dy
I HO
I Er
I Tm
I Yb
0.68 0.65 0.65 0.77 0.65 0.78 0.72
believed to be due to oxidation to cerium(1V). The fact that only cerium tailed badly and then only in more concentrated acid supports this assumption. The R, values for the lanthanide chlorides, Figures 3 and 4, fall in a different pattern than for the nitrates. The R/ values, a t least for the heavier lanthanides, decreased with increasing acid concentration which is just the opposite of the case with the nitrates. The R f values initially decreased for the lighter lanthanides but reached a minimum around 6 M acid and then increased. This resulted in behavior in concentrated acid very similar to what was observed with nitric acid. The largest separation factors were observed in concentrated acid where the Rfvalues decreased from lanthanum to lutetium. Again a singularity was observed with gadolinium and with cerium, the latter only with Concentrated acid. The lanthanide perchlorates were very strongly retained on the HDPMtreated papers and had Rf values of zero unless the mobile phase was strongly acidic. Their movement on glass fiber paper treated with 0.1M
Lu
lanthanide nitrates using ascending chromatography
the paper is not exceeded, even trace amounts of barium and strontium can be separated from much larger amounts of the other members 'of the family. Separation of the Lanthanides. The Rf values observed for the lanthanide nitrates and chlorides as a function of acid concentration of the developing agent are shown in Figures 2 and 3. These results were obtained on Orange Ribbon sheets treated with 0.1M H D P M using the ascending method of development. The R, values for yttrium are not plotted but fell a t the same point as d:isprosium in 9 M nitric and as erbium in 12M nitric acid. They fell a t the same R, as neodymium in 9M hydrochloric and slightly above erbium in 31M acid. The trends in R, values for the nitric and hydrochloric acid systems observed for radial chromatography using Blue Ribbon paper treated with H D P M are shown in Figure 4 for three selected lanthanides. The Rf values for the movement of the lanthanide nitra.tes on HDPMimpregnated paper, Figures 2 and 4, indicate that, as in the case of TOPO (SI),the partition coe,Ecients are higher into H D P M a t low acid concentrations. Above 1M nitric the R, values increase (the partition coefficients decrease) with acid concentration. Unlike TOPO the lanthanide nitrattss are appreciably retained with HDPM and a plot of Rf values as a function (of atomic number reveals a number of similarities to similar plots based 011 the partition of the lanthanides into T B P (15). A distinct inversion in the order of R, values as a function of atomic number occurs, Figure 4, and the separation factor Eletween adjacent lanthanides increasef with acid con-
Acid front
Mg Ca Sr . . . . . . . . . . . . 0.31 . . . . . . ... 0.46 . . . . . . . . . . . . 0.39 . . . ... 0.65 . . . 0.52 0.32 0 . 7 8 . . . 0 . 5 3 0.26 0 . 7 2
Be
centration similar to that observed with TBP. Because the Rf values are becoming larger with acid concentration, no difficulty should be encountered in eluting the lanthanides from columns as Fidelis and Siekierski ( 7 , 8) encountered a t high acid concentrations with TBPtreated column packings. I n agreement with partition data (16) a definite singularity is seen a t gadolinium, Figures 2 and 3, and the slightly higher R f for this element is expected by analogy with the sl ghtly lower than average partition coefficient into TBP. No singularity existed for cerium in the T B P extraction data and the unusually low R, values obtained are
T .I
1
Lo
I
I
I
I
Ce
Pr
Nd
Srn
Figure 3.
I
Eu
I
I
Gd
Tb
1 Dy
I HO
I Er
I Tm
J
I Yb
LU
Rf values for lanthanide chlorides using ascending chromatography VOL 36, NO. 7 , JUNE 1964
b
1227
x
i
HNO3
other two columns and the separation factors are also considerably larger. The free column volume is very closely given by the breakthrough of sodium perchlorate with T B P and TOPO and of potassium chloride with HDPM. A11 the alkali perchlorates show some separation and sodium and lithium are well separated. Barium perchlorate is more slowly eluted than lithium and is not shown in Figure 5 for the HDPMtreated column. I t began to elute immediately after sodium and the maximum (at 22 ml.) was not eluted until \vel1 after the lithium. Magnesium and calcium were tightly retained on the HDPhl-treated column and gave broad elution curves with maxima a t about 60 and 220 ml., respectively. The shape of the elution curves (a relatively sharp trailing edge but a long leading edge) indicated a 16ad dependence not unexpected with water as the eluent. This load dependence is illustrated in Figure 6 for the elution of varying amounts of sodium perchlorate. The data were plotted as above. The increase in elution volume with column load indicates a self saltingout effect. As in the case of paper chromatography dilute perchloric acid displaced strontium and barium from the HDPMtreated column (50 X 0.4 cm.) but not magnesium or calcium. K i t h 0 , l J l perchloric as the eluent, 50p moles of barium and strontium broke through as soon as one column volume of eluent was added. They tailed slightly but were
:I AM Pr.Lu
.I
IM
3M
6M
9M ACID CONCENTRATION
Gd Pr 3M
6M
Figure 4. R, values for several lanthanide chlorides and nitrates using radial chromatography
H D P M and developed with 9M perchloric acid was previously given in Table V. When the acid concentration of the mobile phase was greater than 9M in perchloric acid, it became increasingly difficult to detect the zones after development. The results in Table V indicate that the perchlorates behave somewhat like the nitrates except that no singularity was observed for gadolinium. The Rf valuev for erbium and thulium did break a regular monotonic decrease in R j mith atomic number. Column Chromatography. Elution curves for several Groups I and I1 metal perchlorates on Kel-F columns impregnated with T B P , TOPO, and H D P M are shown in Figure 5 . Water was used as the eluent and the effluent was monitored conductometrically as previously described. The recorder gave a plot of bridge unbalance as a function of time. The pen displacement was roughly linear with concentration and no significant distortion of the elution curves results by making this assumption. The actual d a t a were replotted for Figure 5 arbitrarily assigning a value of one to the concentration of the effluent a t its maximum value for each individual salt. The ordinate then gives the fraction of that concentration a t any other point. The same amounts ( 5 of a 0.1M solution) of all the salts were placed on the column and the difference in area under the various 1228
0
ANALYTICAL CHEMISTRY
curves is a result of the method of plotting the data. All of these perchlorates are held much more tightly on the column with the HDPM-Kel-F packing than on the
MILLILITERS
Figure 5.
Elution curves for Groups I and I1 perchlorates
completely eluted before magnesiu-n started to elute. With 13' perchloric acid, magnesium also eluted immediately but tailed scmewhat and was not completely separa1,ed from calcium which started to elute slightly before two column volumes had passed. The calcium elution curve was very broad with 1M acid. When the acid concentration of the eluent was increased to 3 M J the calcium also broke through immediately. CONCLUSIONS
The three stationary phases investigated (TBP, TOPO, m d HDPPVI) are generally more powerful extractants in the order given. The high partition coefficients of most metal salts into H D P M make this compound particularly suitable for reversed-phase paper chromatography. Tht: small amount of H D P X needed on the paper (approx. 10-6 mole per sq. em.) and the fact it has a low melting p o n t and does not crystallize on the paper are definite advantages. The capillary flow of solvent over the paper does not seem to be affected by treating the paper with this amount of H D P M . A number of otherwise difficult separations can be achieved quickly and simply by means of reversed-phase partition paper chromatography. No sperial equipment or the use of noxious or volatile solvents is required. The problem sometimes encountered in solvent extraction of finding a suitable solvent for the adducts formed is avoided. LITERATURE CITED
(1) Cerrai, E., Testa, C., Energia Nucl. (Milan) 8 , 510 (1961). (2) Cerrai, E., Testa, C., J . Chromatog. 8, 232 (1962). (3) Ibid., 9, 216 (1962).
(4) Cerrai, E., Testa, C., Triulzi, C., Energiu h'ucl. (Milan) 9, 193 (1962).
I
I
I
I
I
I
I
pMOLES OF N o C W ON COLUMN
t;
2kl0 b
I
I
I
I
I
I
33% HDPM ON Kel-F(60-EOMESH),5g ELUTING AGENT- WATER COLUMN LENGTH- 5 0 crn I D - 0 4 crn FLOW RATE - 0 4 8 r n l / r n i n . TEMP 25'C
g 8
z
i 6
u $ w4
2 $ 2
a I
Figure 6.
2
3
4
5
6 7 8 MILLILITERS ELUTED
9
IO
II
!2
13
Elution curves of sodium perchlorate as a function of column load
(5) Ibid.,,p. 377. (6) Dietrich, W. C., Caylor, J. D., Johnson, E. E., U . S . At. Energy Comm. Rept. Y-1322 (1960). (7) Fidelis, I., Siekierski, S., J . Chromatog. 4. 60 ii96n). (8j'~&.', 5,-ibi (1961). (9) Fletcher, W., Franklin, R., Goodall, G. C., U . S . At. Energy Comm. Rept. TID-7629,276 (1961). (10) Fritz. J. S.. Hedrick. C. E.. ANAL. CHEM.34, 1411 (1962). ' (11) Gwbhdf, R., Siekierski, S., N u k leonzka 5 , 671 (1960). (12) Hamlin, A. G., Roberts, B. J., Loughlin, W., Walker, S. G., ANAL. CHEW33, 1547 (1961). (13) Hayes, T. J., Hamlin, A. G., Analyst 87. 770 f 1962). ~
(20) Mikulski, J., Strofiski, I., Nukleonika 6, 295 (1961). (21) Ibid., p. 775. (22) Naito, K., Suzuki, T., J . Phys. Chem. 66, 989 (1962). (23) Oshima, K., J . At. Energy Soc. Japan 4, 8 (1962). (24) Pierce, T. B., Peck, P. F., Nature 194, 84 (1962). (25) Ibid., 195, 597 (1962). (26), Richard, J. J., Burke, K. E., 0 Laughlin, J. W., Banks, C. V., J . Am. Chem. Soc. 83, 1722 (1961). (27) Siekierski, S., Sochaka, R. J., Polish Acad. Sci., Inst. Nucl. Res. Rept. 262-V, 1961. (28) Small, H., J . Znorg. Nucl. Chem. 18, 232 (1961). (29) Ibid., 19, 160 (1961). (30) Testa, C., J . Chromatog. 5 , 236 I 1 961 \. \ - - - -
(31) White, J. C., Ross, W. J., U . S . (1959): (16) Ishimori, T., Kimora, K., Fujino, T., Murakami, H., J . At. Energy SOC. Japan 4, 117 (1962). (17) Ishimori, T., Watanabe, K., Nakamura, E., Bull. Chem. SOC.Japan 33, 636 (1960). (18) Katzin, L. I., J . Inorg. Nucl. Chem. 4,187 (1957). (19) Kuznetsov, V. I., Compt. Rend. Acad. Sn'. U.R.S.S. 31, 898 (1941).
At. Enerau _ _ Comm. Rept. NAS-NS-3102
(1961). (32) Winchester, J. W., U . S . At. Energy Comm. Rept. CF-58-12-43(1958). RECEIVEDfor review December 2, 1963. Accepted March 18, 1964. Division of Analytical Chemistry, 142nd Meeting, ACS, Atlantic City, N. J., September 1962. Work performed in the Ames Laboratory of the U. S. Atomic Energy Commission.
Mechanism of Electrophoretic Migration in Paper J. CALVIN GlDDlNGS and JAMES R. BOYACK Department o f Chemistry, University of Utah, Salt lake City 72, Utah The factors contro'lling the mobility of charged species in media composed of swelling fibers (especially in paper electrophoresis) have lbeen investigated theoretically. Mobility is influenced by three factors, none of which are negligible. First is the tortuosity as originally proposed by Kunkel and Tiselius. Second is the constrictive effect proposed by the present authors. Third is the ion retardation factor which has not previously been formulated. Using a cell model, theoretical expressions are derived for these effects which show their relative importance under various conditions.
The theoretical concepts developed here are used as a framework for the discussion of previous theories, particularly the tortuous path theory and the barrier theory.
P
REVIOUS THEORIES of
electrophoresis have centered around the tortuous path concept of Kunkel and Tiselius (7) and the barrier concept of McDonald (8). The present authors (3, 6 ) have recently extended these theories to include a number of important considerations heretofore neglected. I n regard to the tortuous path concept a constrictive factor, arising from the
variable cross section of a migration channel, affected the migration rate to approximately the same extent as tortuosity, and the two could be combined to yield very satisfactory values for the zone mobility (3). I n the case of the barrier concept, a quantitative theory was developed (6) to show the effect of diffusion in skirting barriers, and the mobility depends upon the applied potential providing the latter is sufficiently high. Synge (1.4) first suggested the concept that escape from barriers occurred by diffusion. The fundamental relationship of the tortuous path and the barrier concepts YOL. 36, NO. 7, JUNE 1964
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