Plastic Conical Columns for Chromatography
H. M. Stahr, R. M.
Ikeda, E. T. Oakley, and B. M. Carter, Philip Morris Research Center, Richmond, Va.
hromatographic columns of various shapes and volumes have been used to fill the analyst’s particular need. A good reference ( 1 ) is available for column preparation. A plastic cone provides a desirable adsorbent shape to minimize the band volume which the chromatographic fraction occupies. Columns may be stacked to allow the use of even larger volumes of adsorbent. Described below is an experiment using an adsorbent and marker to compare conical columns with cylindrical columns containing the same weight of adsorbent. EXPERIMENTAL
Materials. The following materials were used: Eastman white label azobenzene; Fisher Spectrograde hexane; Matheson, Coleman, and Bell Spectrograde benzene; Brinkmann silica gel, size 0.2 to 0.5 mm., catalog 7’#773. Apparatus. The apparatus consisted of: a cylindrical glass column, 8 inches long, 1 inch in diameter with a $2 stopcock of Teflon fluorinated hydrocarbon polymer attached a t the bottom; a three-section glass column 12 inches in overall length: the upper section ‘/s-inch i.d. and 4 inches long; the middle section, 3/&ch i.d. and 41/2 inches long; and the bottom section, 1/8-inchi.d. and 3f/zinches long.
A glass bead was used to constrict the lower section about inch from the bottom to control the flow and prevent the loss of adsorbent (Figure I). A conical polyethylene column was also used (the column is called a Polycone and is a joint adaptor manufactured by the Nalgene Co.) 103/4inches long, 11/8-inches i.d. a t the top, and inch i.d. at the bottom. The column has a 12/30 joint with a Teflon stopcock (#2) attached a t the bottom to control the flow (Figure 1). Procedure. The columns were slurry packed with 20 grams of silica gel taken directly from the storage bottle without any heating. The slurry was made in hexane. After the columns were uniformly packed with the slurry and washed with 100 ml. of additional hexane, one drop of 1% azobenzene in benzene solution was added to each column and washed onto the column with a little hexane. The azobenzene was then eluted by adding 15% benzene in hexane to the top of the column and allowing the solvent to flow from the column at maximum velocity. When the solvent became colored, the colored liquid was caught until it again showed no color. The volume of the colored liquid was measured. This volume was taken as the band volume in each column. The height of the gel in the cone was g1/2 inches, in the multistage column it was inches, and in the cylindrical column it was 31/2inches.
I
I
RESULTS AND DISCUSSION
A
Some results obtained with the columns are shown below.
Table I.
Column Design
Column Three-stage column Conical column Cylindrical column
Flgure 1 , umn
1974
a
Cylindrical multistage col-
ANALYTICAL CHEMISTRY
Band volume, ml. Run1 Run11 47 53
48
110
115
55
From Table I the one-stage conical column is seen to be superior to the cylindrical column and nearly as effective as the much slower multistage column. The rate of flow can be critical in an analysis where a substance is reactive enough to be degraded during isolation. The conical column can also be run a t a lower velocity if desirable. The experiment shows that the conical column is superior to the cylindrical column and is nearly as effective as the multi-stage column. This effectiveness coupled with
Figure 2.
Pressurized conical column
its relatively fast rate make the column useful where reactive substances, which degrade during separation, are being separated. Pressure may be applied by means of the inlet pressure assembly shown in Figure 2. The conical column is especially useful where a large volume of adsorbent must be used because of the presence of a high concentration of deactivating substances. ACKNOWLEDGMENT
The glass blowing was done by John Bivins. LITERATURE CITED
(l).Gordon, A. H., Eastoe, J. E., “Practical Chromatographic Techniques,” Butler and Tanner, London, 1964.
