An ave:age of inree scans was used :a determine ihe diffusion current before and after the aadirion of the standard soiution. In this manner, the number of variables was reduced and the aminocaproic acid content of the extract solutions was determined by the following equation:
C,hrr H(V G) - hV where C, = concentration of standard solution V = volume of sample solution c = volume of standard solution added h = diffusion current before addition of standard solution H = diffusion current after addition of standard solution
c,
=
~
+
The results of the analysis of known aminocaproic acid solutions may be seen in Table I.
Samples of production grade nylon polymer were analyze< in the manner described above. As may be seen in Table II, the aminocaproic acid content was found to be in the iower end of the concentration range reported by Hermans and coworkers. This is a reasonable figure as production grade polymer is leached to remove most of the water soluble material, while those polymers examined by Hermans and coworkers were not washed and would contain a higher percentage of the amino acid. There was observed a sample to sample variation in the analysis of the production grade polymer. This is probably due to slight variations in extraction during the sample preparation.
RECEIVED for review January 6, 1967. Accepted March 13, 1967. Division of Analytical Chemistry, 152nd Meeting, ACS, New York, N. Y.,September 1966.
separation of Petroleum Hydrocarbons by Selective Adsorption with Sephadex LH-20 Beveridge J. Mair, Philip T. R. Hwang, and Raffaele G . Ruberto Petroleum Research Laborator), Carnegie Institute of Technology, Pittsburgh, Pa. SILICA GEL and alumina appear to be the favorite adsorbents for the fractionation of petroleum hydrocarbons. The separation of paraffins and cycloparaffins from aromatics can be effected quantitatively by adsorption on silica gel and a nearly complete separation of aromatics into mononuclear, dinuclear, trinuclear, and higher nuclear aromatics is possible with alumina. However, the separation of the sub types such as the paraffins from the monocycloparaffins or the alkylbenzenes from the monocyclanobenzenes is much more difficult and for this purpose neither silica gel nor alumina is effective. For many binary mixtures of a paraffin with a cycloparaffin, with silica gel or alumina as adsorbents, one of the components is preferentially adsorbed in a part of the concentration range, there is one concentration a t which neither component is preferentially adsorbed, and in the remainder of the range the second component is preferentially adsorbed ( I , 2). Thus a complete separation of paraffins from cycloparaffins is not possible irrespective of the number of stages in the fractionating column. This report describes the separation of paraffins from cycloparaffins and alkylbenzenes from cyclanobenzenes by selective adsorption on Sephadex LH-20. Heretofore, Sephadex LH-20 has been used primarily with the technique known as gel filtration chromatography for the separation of molecules according to their size. However, it has been recognized that Sephadex LH-20 possesses selective adsorptive properties. For example, Wilk et ul. (3) in experiments with Sepliiiclcx LH-20 expanded with 2-propanol have hewn th;it thc rctcrition volumes increase with inc.rc;ising i'iiig coiitcnt for the .
(I) 13, J . blziir, A . I . C ~ i i l ~ ~ r i ~:iricI i u l i ,I . I ) . l
