indicates that the presence of a modified adsorbent surface is a more logical assumption and is consistent with previous studies involving moderately polar solutes and substrates
(4-6). 0.8
0.6
I .o
I
2.0
I
3.0 PIPo x 102
I 4.0
I
5.0
Figure 7. Sorption isotherms at 55 “C for methanol on Chromosorb P coated with 19.8 TOTP Curve identities are the same as those for Figure 4
reasons, among which may be a mass action effect or a partial blocking off of the support surfaces in the finer capillaries. Unsaturated impurities in the untreated squalane may have caused some of the anomalies, especially at the higher liquid loads. Figure 7 represents our most recent work and shows that the additive relationship also holds for methanol on TOTPcoated Chromosorb P. A number of other solutes, solvents, and supports are being studied and their relationship will be reported at a later date. CONCLUSIONS
The new details of sorption processes on liquid-coated adsorbents discovered in these studies should help develop new avenues of approach to applied and research activities in the fields of chromatography, catalysis, adsorption, and biochemistry where the special properties of large specific surface areas are of concern. The existence, under the conditions of the experiments reported here, of a new, apparently independently acting, adsorbing surface formed by a small fraction of the coating liquid should help in the understanding and development of surfaces with special physical or chemical properties. At this point, the new relationships seem t o be more easily recognized in those systems where a polar liquid solvent competes more strongly for the active adsorption sites than does the solute molecule. A minimum in the sorptive capacity of the system which occurs at low percentages of liquid coating remains constant. As the per cent coating is increased, the sorptive capacity of the increasing layers of the covering liquid adds to the minimum sorptive capacity. At no level of increasing per cent liquid load does this primary sorptive capacity appear to decrease, nor is there evidence that the sorptive capacity of the system as a whole decreases or increases as the surface area of the coating liquid becomes smaller or larger with per cent liquid coating. This eliminates the possibility of adsorption by the liquid surface as a significant factor. It
1134
ANALYTICAL CHEMISTRY
The data for the squalane-coated supports are interesting in at least two aspects. They move vividly show the competitive nature of the liquid-coated support for a solute in that the amount of acetone sorbed is not largely affected by the presence of the larger nonpolar squalane molecules. The data also show that acetone, which is only slightly soluble in solulane, easily penetrates the squalane to be sorbed by the underlying surface. Empirically, practitioners in gas chromatography have long used small percentages of subcoating substances such as stearic acid and polyethylene glycols or trimethyl silanization t o reduce the tailing effect of surface active supports (13). Such procedures lead to the formation of a modified and less active sorbent surface. Whether the magnitude of the additive effect of such a surface is large enough to be recognized in ordinary gas chromatographic methods or in measuring thermodynamic functions is a matter of conjecture and of continuing interest to us at this point. RECEIVED for review February 1, 1968. Accepted March 29, 1968. This investigation was made possible by a National Science Foundation Grant No. GP-5400.
Correct ions Potentiometric Measurements with CalciumSelective Liquid-Liquid Membrane Electrodes In this article by G . A. Rechnitz and Z . F. Lin [ANAL. CHEM., 40,696 (1968)l an error appears on page 699, column 2, just preceding Reaction 8. The value of k111 is given as 1.3 x 101lM-’ sec-1 but should have the units of 1.3 X 10 lM- sec-1.
A Technique for the Evaluation of Systematic Errors in the Activation Analysis for Oxygen with 14-MeV Neutrons In this article by S. S. Nargolwalla, M. R. Crambes, and J. R. DeVoe [ANAL.CHEM.,40, 666 (1968)l an error appears on page 667, column 1, line 6. The line should read “NO= Avogadros Number 6.023 X loz3.” Also, on page 667, “ Wt” “ Wt” Equation 3, for __ read -. U V
