Correlationi of R, Values in Pairs of Paper Chromatographic Partition Systems
SIR: Recently, Connors (4) described a method of prediction of RF coefficients for rela,ted substances in new solvent systems. He derived an equation relating the RF values of a solute in two partition chromatographic systems; assuming a constant ratio of partition numbers for a series of solutes (Gy/GX = F = constant, where Y and X denote two partition systems), a regular correlation of the two sets of RF values is obtained. The assumption is often valid for substances of similar structure, particularly those possessing identical groups capable of hydrogen bonding with solvent molecules. It seems that interesting results could also be obtained by substituting RF coefficients by R M values. The latter are related in a simple way to the difference of standard chemical potentials of the solute in the two phases, much simpler than is the case for RF coefficients; thus, the RM values in two solvent systems can also be expected to give a simpler correlation than RF coefficients. I n fact, an empirical equatilon has been given by Collander (3) which implies a linear correlation of log partition coefficients ( k ) in two partition systems: log kY
=
a(1og k X )
+b
This equation, found valid for a number of cases, has been theoretically substantiated by Buchowski (2) on the basis of the thermodynamic theory of solutions. A similar correlation is often used in gas liquid partition chromatography, where logarithms of retention times are plotted on the two coordinate axes. -4s can easily be shown, an
1.o
1
0.5
I
0.0 RMG
-1.5
-1.0
0.0
-1.5
0.5
1.0
RM*
Figure 2. RM correlation for barbiturates in solvent systems F and G See (41 for data and notations
analogous relationship can be derived from Collander’s equation. (This assumes certain simplifications; cf. also Kabasakalian and Basch (5) who found empirically the same relationship between RM values calculated from the . values additivity principle, and RM determined experimentally for six other solvent systems)
+ constant
R M y= a(RMX)
A linear correlation is thus obtained for RM values. If it is also assumed that the ratios of partition numbers ( F ) of the solutes are constant, then the last equation simplifies to
R M =~ R M -~log F That is to say, a straight line of unit slope is obtained. The last equat.ion can be derived simply from the definition of the RM coefficient (1). Since RF is equal to the fraction of solute in the mobile phase, and 1 - RF equals the fraction of solute in the fixed phase, we have
To give an experimental illustration of these relationships, RM values were determined from the data used by Connors [for notation, composition of solvent systems, and references, cf. (4)1. Macek’s data on barbiturates represented as R . T R ~ plots are given in Figures 1 and 2. In accordance with the regular RF-RF correlation obtained by Connors, corresponding linear RM-R~ relationships are seen, the slope of the lines being close to unity (compare with the simplified equation). The R,TR.V correlation for the condensed phosphates is represented in Figure 3. It is also linear; however, the line is less steep and the coefficient a is well below unity. The correlation is clearly F more regular than the R ~ R relationship [cf. (4,Figure 31, although the solvent systems are rather complex ones. I have not tried to transform the data for the uracil derivatives [cf. (4,Figure 41; however, I suppose that these data would also give an approximately linear RIK-R.wrelationship. Yote that in all three plots Reichl’s definition of RMis used (R’M=
-Ru).
Concluding this note it may be worth pointing out that R.M values, although less convenient for purposes of analytical practice, give usually much simpler relations not only in structural studies ( I ) , but also in studying the effect of phase composition (6) and, as illustrated in this note, in correlation of chromatographic behavior in different solvent systems. Plots of this type, with suitably chosen pairs of partition systems, may provide information concerning the molecular interactions of solutes and solvents and thus also their molecular structure, as has already
0.5
-
0.0
-
-1.5
RM=
RnrX = log
1 - RrX ___
R F ~
-
- log GX
Thus, by subtracting the two equations 0.0
0.5
1.0
1.5
RME
RMY
- RMX
=
- log GY + log GX
Figure 1 . RM corirelation for barbiturates in solvent systems € and F See ( 4 ) for do to and nototions
RMX - log F
-1.0
-p.5
-
t
-9.5
-1.0
-1.5
0.0
0.5
RMC
Figure 3. RM correlation for condensed phosphates in solvent systems C and D See (4) for data and notations
VOL. 37, NO. 1 1 , OCTOBER 1965
1439
been reported for gas liquid partition chromatography. In most works concerning partition chromatography the authors substitute freely the rational partition coefficients following from Nernst’s law (Zk = z1/z2, concentrations expressed in mole fractions) by the ordinary partition coefficient which is employed in the theory of partition chromatography (k = c1/c2, concentrations expressed in mole/volume scale). Even the same symbol, a, is used to denote the two
coefficients. And yet the coefficients Dissert. Univ. Warsaw, NO. 4, PWN are not identical: zk = I c ( s 0 / u 2 0 ) where Warsaw, 1963. ( 3 ) Collander, R., Acta Chem. Scand. 5, soJu2O are the molar volumes of the 774 (1951). two phases and the solutions are (4) Connors, K. A., ANAL. CHEM.37, 261 (1965). assumed to be dilute [cf. Buchowski (D]. ( 5 ) Kabasakalian. P.. Basch., A.., Ibid.. 32, 458 (1960).’ ’ (6) Soczewinski, E., Chem. Anal. (Warsaw) 8, 337 (1963).
LITERATURE CITED
(1) Bate-Smith, E. C., Westall, R. G., Biochim. Biophys. Acta 4, 427 (1950). (2) Buchowski, H., The Effect of. the Properties of Solvents on Partition Coefficients of Nonelectrolytes between
Water and Organic Solvents (in Polish),
EDWARD SOCZEWINSKI Department of Inorganic Chemistry Medical Academy ul. Staszica 6. Lublin, Poland
Analysis for Microgram Quantities of Thorium in Plutonium Neptunium and Uranyl Nitrate Solutions SIR: Process tests for separating the uranium-233 values from irradiated thorium oxide fuel are to be carried out in the Purex process (6). After each test, thorium impurities must be detected and measured in the normal process products; plutonium, uranium, and neptunium nitrates. Because of the low specific activity of natural thorium232, radiometric means of detection do not apply in trace quantities. The colorimetric technique to be used, thoron, required a well-purified thorium fraction, since gross quantities of the above named products would interfere seriously. A large number of thorium separations techniques have appeared in the literature. Two very good reviews have been published (2, 4). Ion exchange techniques predominate in the more recent publications. A cation exchange procedure (11) using strong hydrochloric and nitric acid eluents for selective stripping has been reported. Anion exchange methods are based on formation of the thorium nitrate complex (1, 6) ; an ascorbinate-thorium complex (6) ; the sulfate complex (3); or the nonformation of a thoriumhydrochloric acid complex (7). The latter case is most attractive because only the column effluent must be accumulated, with no long elution period to be observed. Plutonium(II1) is the only other major element of interest that would not be absorbed on the anion exchange resin.
Table
I.
Liquid-liquid extraction is more desirable than ion exchange since less time is used to make the separation. Use of a tertiary amine to extract uranium from a sample followed by a primary amine extraction for thorium was reported by Petrow, Sohn, and Allen (8). Ross and White (9) discussed an extraction with tri-n-octyl phosphine oxide (TOPO) from solutions containing sulfate and phosphate. The same authors published a review (10) of cation separations with TOPO. Because large sample volumes would be required to find the thorium contaminate in gross concentrations of plutonium, uranium, and neptunium, the probable need for a two-cycle purification of thorium was considered. An anion exchange adsorption from a hydrochloric acid matrix was considered for the first cycle gross separation; while thorium would not be retained on the resin, most other elements should be. Elimination of an elution step would reduce the time required to complete this cycle. The final thorium purification would be accomplished by liquid-liquid extraction with TOPO. EXPERIMENTAL
Reagents. The chloride form anion exchange resin, AG 1 X 8, 100 to 200 mesh, was obtained from the BioRad Co. in a n analytical grade. The resin was preconditioned with 9 M hydrochloric acid prior to use.
Thorium Decontamination from Plutonium(lll) and (IW, Neptunium the Uranyl Ion
c./m. in ion exchange Element Pu239(III) Pu239(IV) NP2YV) UZ3302+e
1440
c./m. taken 7.08 X lo7 8 . 6 7 x 104 2 . 4 4 x 107 1.59 X 108
ANALYTICAL CHEMISTRY
effluent 5 . 4 9 X 106 1 . 5 6 x 103 160 1.57 X 106
c./m. in 0.01M TOPO 2 . 2 5 X lo6 96 16 1 . 5 6 X 106
(‘4,
c./m. in HCl strip
and
1.12 x 106
