knurled ring wbich clamps the spectrometer onto i t are the only parts of the existing instrument which are altered, Mthough the limited space available dictates a very compact design, the valve opening is more than sufficient to pass the full solid-angle of x-rays, as defined by the standard rotary aperture in fully-open position.
Complete detailed drawings of the valve assembly, as designed for the Cambridge electron probe, will he provided by the authors on request.
LITERATURE CITED
(1) Cambridge Instrument Co., Ltd., 13 Grosvenor Place, I>ondon, S.W. 1, "The hlicroscan X-Ray Anslyaer (Mark
II)," 1SR1.
(2) Duncnmb, P., nklford, I ) . A,, "x-nay
ACKNOWLEDGMENT
We thank J. n. Reynolds for fahrication of the valve.
Microscopy and X-Ray Microanalysis," Engstrom, A,, Cosslett, V. H., Pntke, H. H., &., mevier, pD. 353364. Amsterdam, 1960.
An All-Glass Coupled Column for Larsje-Scale Chromatographic Separations
0.William
Berg, Department of Chemical Engiineering and Applied Chemistry, University of Toronto, Toronto 5, Canada
a column conT slstmg . of a series of individual columns of successively decreasing HE COUPLED COLUMN, '
volume, was described first by Claesson ( 1 ) and Hagdahl (8). A recent review is also available (3). A high-capacity column with superior separating ability can he assembled using slightly modified standard components of industrial flanged-glass pipe (Figure 1). For the use with aqueous solutions no modification is necessary, apart from the addition o f a stopcock. Figure 2a depicts an all-metal threestage coupled column according to Hagdahl. The shaded area indicates the absorbent. The individual columns are connected to each other t y threaded capillary couplen. Figure 2b shows how such a column can be simulated by using standard fittings of flanged industrial glass pipe. The corresponding parts are joined with horizontal lines. These parts are in descending order: hose connector, not shown in Figure 26 hut in Figure 4, straight length of pipe, reducer, length of pipe, reducer, length of pipe. Finally, the lower end is closed with a stopcock, not shown. Clearly, the reducer has to be modified to incorporate the capillary. The easiest way to accomplish this is to insert a plug, a cylindrical piece of an inert material--e.g., polyethylenewith a suitable hole drilled through it. Such a design is shown in Figure 3a. The plug is indicated by the shaded area. Unfortunately, the upper rim of the reducer has a somewhat smaller diameter than the inner part of the tubing. Consequently, the plug has to he elastic. With aqueous solutions this type of construction works well. The addition of a stopcock produces then an exeellent coupled column of any desired capacity. With organic solvents, this design is less desirable as the plug swells. Consequently, an all-glass construction was adopted (Figure 3b). Efforts should be made to make the upper part of the capillary section flat, as this supports the filter paper disk, used to prevent adsorbent flow to the column below. Table I summarizes the parts used to 774
ANALYTICAL CHEMISTRY
hnild a five-section coupled column. The fittings up to 0.75-inch nominal diameter were supplied by Sentinel Glass Co., Hathoro, Pa., while the larger sizes were supplied by Q.V.F. Glass (Canada) Ltd., Searhorough, Ontario. The latter brand of pipe fittings is to he preferred for the larger sizes; actually the smallest diameter available is 5/s inch, as the pipe sections are available in 1-inch increments from 6 inches up to 12 inches. For borosilicate glass (Corning) the smallest availatle diameter is 1 inch. The stock lengths increase in &inch increments from 6inch sections. The gaskets are of the Teflon (Du Pont) envelope type. They should he of the machined type rather than the split variety. The latter ones have a slightly smaller diameter than the corresponding fittings. The stopcock used to close the smallest column section has a plug of Teflon. Actually, a variety which also incorporates a needle valve is to be preferred as occasionally the flow rate adjustment with the ordinary stopcock is somewhat time consuming. The top of the column is closed with a standard hose connector (Figure 4). The construction is apparent from the figure. The shaded area is a short length of heavy rubber tubing. An all glass ring seal could he envisaged between the glass tubing leading to the pump and the connector. This type of seal is preferable &s it acts as a safety valve in case the pump is turned on and the stopcock is not opened. The complete five-section column can he filled with about 600 grams of alumina. This is sufficient for the separation of at least IOgramsofsample. It is seldom necessary to use all five sections. With additional fittings, stopcocks, and connectors, any suitable combination of the columns can be used. Figure 1 shows a three-section b OvercVIIview of 3-section (0.5, 0.75, and 1 inch) column fed b y Figure 1 .
bellows pump
column, sections 2, 3, and 4, in operation. The additional part is the stopcock attached to a 0.5-inch pipe flange. The top is closed with a Liebig type of seal. The connector is, however, an improvised one.
a
b
Figure 2. a. Metal coupled column (3section) according to Hagdahl
Section
Table I.
Parts Used to Build Five-Section Coupled Column
Length, cm.
Diameter (nominal) inches
Vol., ml.
Val. ratio
35
0.25
12
...
22
0.50
28
2.3
24
0.75
79
2.8
28
1
142
1.8
25
1.5
283
2.0
clean from the sorbent particles, and the coupler with its gasket is fitted. The rest of the column section is then filled through the capillary. There should be a sorbent-free space filled
Shaded areas represent adsorbent
b. Corresponding parts of flanged industrial glass pipe
Q
b
Figure 3. 0 . Coupler using elastic insert (shaded area) for aqueous solutions b. Construction all-glass coupler
of
The column is fed with a simple bellows pump. The connection to the column is made with spaghetti-tubing of Teflon. With this type of pump, the flow is of course pulsating. However, if sufficient air space is left at the top of the sorbent, ordinarily filled with glass wool, the flow is quite even through the column. The moit useful combination of the column sections was found to be one, two, and three. The filling of the column with about 100 grams of alumina enabled the separation of approximately 3 grams of material. Filling and Operation of Coupled Column. The column is filled in sections. The alumina is added as a slurry to the column, beginning with the smallest section. It is essential that the sorbent not be allowed to fall through a column of solvent, as sedimentation according to grain size will take place. Once the section is filled, the flange I$ carefully wiped
Figure 4. Closure of column using Liebig type seal Shaded a r e a represents heavywalled rubber tubing
Overall length, cm.
Coupler length of I.D. of capillary, capillary, mm. mm.
9.5
25
9.7
30
12
31
19
45
with solvent below the capillary section of the coupler. How much the sorbent settles, and this determines largely the volume of this space, is a matter of experience. h’ext, a disk of hardened filter paper is placed on top of the capillary, and the filling is continued. -1lengthy conditioning of the column is not necessary. Allowing the column to stand overnight is sufficient. On the other hand, the use of freshly prepared columns gave erratic results. This type of column has been used by the author over a number of years to separate bi- and polypyridyl compounds on alumina using mixtures of petroleum ether and benzene as eluents. Finally, the author also experimented with and obtained excellent results with a design shown in Figure 5 . This type of column, quite small in size, was used with gradient elution t o determine suitable solvent systems for the mixtures at hand prior to the large-scale separations on the coupled column. The operation of this type of column is self-evident. The plugs of Teflon (black in the Figure) are pushed down the column with a piece of glass tubing, and are removed with a wood-screw soldered to a long brass rod. For the successful design of this type of column, it is essential to realize that most commercial glass tubing is slightly conical. Clearly, for tight fit of the plugs it is necessary to choose the tubing so that it is conical downwards. In addition, the connections of the sections should be made on a lathe. This type of column is far superior to a simple Tswett’s tube of similar capacity. I t has been used extensively in the separation of multicomponent mixtures obtained from the methylation of 2,2’-bipyridyl with methyllithium.
LITERATURE CITED
Figure 5. One-piece coupled column Shaded areas represent adsorbent and black areas the inserts of Teflon
( 1 ) Claesson, S., Arkiv Kemi, Mineral. Geol. A24, N o . 16 (1947). (2) Hagdahl, L., Acta Chem. Scand. 2, 574 (1948). ( 3 ) Hagdahl, L., “Chromatography,” E. Heftmann, ed., Reinhold, New York, 1961. VOL. 37, NO. 6. M A Y 1965
775
