a S/Tinch i.d. hole, required passage of 0.5 ml. and 0.9 ml. to reach 90% and 99% of steady state after a change from 0.2M NaCl to 0.0liM CdC12 in 0.2M NaC1. A flushout volume of about 1.0 ml. was required to bring the current to 0.1% of its steady state value above hackground after a change from 0.01M CdCla in 0.2M NaCl to 0.2M NaCI. Axial holes larger than inch have a tendency to hold gas bubbles and are not recommended. ACKNOWLEDGMENT
200
0 120 160 IATF (MI /MIN )
Thanks are extended to M. Evenson for his help in machining of the cells.
Figure 3. Variation of limi LITERATURE CITED Figurer on ~ u r v e sdenote intern01 d 0.01M. CdCldI.ZM NaCl
ohms at a flow rate of about 200 ml. per minute, when 6 M NaCl was used as the electrolyte in the Ag-AgCI reference electrode, and when 0.2111 NaCl was the flowing sample solution. Gas bubbles that enter the system are not trapped, but because of the small diameter of the axial hole, are carried
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ruption of the polarographic current. This is a very convenient characteristic, for it permits the cell to function unattended for long periods of time. Cells with larger axial holes were also constructed and studied. A cell identical to that of Figure 1, hut with
(1) Blaedel, W. J., Strahl, J . H., ANAL. CHEM.33, 1331 (1961). (2) Parker, W. J., Metal Ind. loo, 82 (1962). (3) Tamamushi, R., Momiyama, S., Tauaka, N., Anal. Chirn. Acta 23, 585 (1960).
Work supported in part by grant No. AT(ll-1)-1082 from the Atomic Energy Commission.
Useful Thin layer Chromatogra P'i y Techniqul T. L. Brown and J. Benjamin, Research Di
I.
N THE PHARMACEUTICAL INDUSTRY it 1s mandatory that the most powerful separatory techniques known he utilized to establish the purity of organic compounds. This is particularly true of the finished products sold to the public.. I t is also a necessary condition prior to the preliminary pharmacological evaluation ' of new synthetic organic substances. Thin layer chromatography has great utility in modern research chemistry because of its separatory efficiency, rapidity, simplicity, and relatively low cost. When one is analyzing large numbers of new synthetic organics with markedly different- chemical properties, it 'is convenient to use a nearly universal detect-
ing agent. It is the practice in this laboratory to spread a thin layer of silica-gel G onto borosilicate plates and then locate the spots on the developed chromatogram by charring the organic substances over a Bunsen burner flame subsequent to spraying with a sulfuric acid plus dichromate solution. This solution is prepared by saturating concentrated sulfuric acid with sodium dichromate and then diluting 1 part of this solution with 5 parts of concentrated sulfuric acid. It has been reported elsewhere (4),that aluminum plates coated with silica-gel G can be used satifactorily with sulfuric acid spray. It has been found in this laboratory that the commercially available silicagel contains smsll amounts of organic
on the acid-sprayed chromatogram (Figure 1). A number of techniques have been evaluated to eliminate this interference. One effective method of eliminating this interference has been described in the literature (3, 6 ) . This method consisted of prewashing the chromatoplate with a suitable solvent prior to use. This was accomplished by placing a chromatoplate in a chromatographic development chamber containing a small quantity of solvent. The solvent was allowed to flow, by capillary action, up the entiie length of the chromatoplate. The purified plate was then dried, activated, and used. This procedure, altbough effective, is unnecessarily wasteful of time and equip-
Figure 1. Chromatogram that was not methanol washed prior to development
Figure 2. Chromatogram that was methanol washed prior to development
Figure 3. Chromatogram illuminated b y reflected light only
446
ANALYTICAL CHEMISTRY
ment. A simple and satisfactory alternative solution to this problem has been developed in this laboratory. It is. as .. IOUOWS: suosequent to spreaumg, arying, and activation ( 1 ) of the silica-gel G, a solution consisting of 20 v./v.% diethyl ether plus 80 v./v.yo met,hanol is allowed to flow across the plate a t right angles to the intended direction of solvent flow during development of the chromatogram. The solvent is then
across the width of the chromatogram during development. A number of procedures are in use for preservation of thin layer chromatograms. One group (8) removed the silica-gel area defined hy the spot and then copied the plate, using a Xerox 914 office copier. Another worker (5) suggested spraying the surface of the chromatograms with a plastic spray which could then be peeled off and filed. Where one must maintain a work reco7.d that is legally validpie., a direct copy of the results miniaturized for filing convenience and capable of replication a t will-photography of the plate seems to be the optimum method available. The photographic result is improvedi.e., trace contaminants are more clearly seen if the illumination is from beneath as well as above the plate. A conventional 8- X 11-inch x-ray viewing box
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substance without disrupting the surface of the thin layer (Figure 2 ) . It is also the practice in this laboratory to scribe channels near the edge of the-plate in the direction of development of the chromatogram. Eliminating the edge effects i n t h i s manner tends to promote uniform solvent flow rates
is a suitable apparatus for viewing the plate by transmitted light. Figures 1 and 2 were illuminated in this manner, whereas Figure 3 was photographed using reflected light only. The differences in the results obtained are quite apparent. LITERATURE CITED
( 1 ) Bekersky, Ihor, ANAL.CHEM.35, 261
"963).
Hilton, J., Hall, W. B., J . Chromatog.
Snyder, Fred, ANAL
A Multiple-Port Fraction Collectc)r for Gas Chromatogral R. L. Hoffmann' and A. Silveiro, Jr.,2 DelJartment of Food Science, Rutyrl., RECENT ADVANCES in the techniques of gas Chromatography has come a need for multiple fraction collection. Many gas chromatographs, while providing components of extreme punty, still lack suitable low-cost collecting devices. Commercial collectors, usually limited to less than 10 fractions, have been used successfully; but high cost and limited fraction capacity have restricted their widespread acceptance. An inexpensive manual collector would be welcomed in
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many laboratories where conditions do not require the more elaborate and expensive devices. The described collector is simple in design and has the capacity to handle 10 fractions with high collection efficiency.
ITA
CONSTRUCTION
The heart of the collector is a smallbore B-D manifold system which d e livers the chromatographic effluent from the detector to the collection traps. The manifolds, available on special order from Becton, Diekinson & Co., Rutherford, N. J. (as per their sketch No. SH-486), are constructed with high temperature solder and are capable of leakproof operation at pressures up to 50 p s i . These nickle-plated brass manifolds use silicone lubricated stop-
Present address: Department of Agriculturitl Biochemistry, Rutgers, The State Univemity, New Brunswick, N. J. Present addma: Department of Chemistry, State University College, Oswego, N. Y.
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cessfully without lubricant. Two B-D type XMSM5 manifolds connected with an X625 rotating adaptor are fitted into a machined aluminum heater block (Figures 1 and 2 ) . Ten MLL/ MLL adaptors allow connection of the female LUER-LOK ports of the manifold to the trap delivery needles. The manifolds, when so placed in the block, are heated by means of two quartz immersion heaters inserted into holes drilled in the ends of the heater block. These heaters, controlled by a variac, conveniently maintain the manifolds at any temperature desired, from ambient to 300" C. Manifold temper& ture is measured by placing thermometers in wells drilled in the heater block just behind the manifold channel. Each thermometer rests only 0.75 mm
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Figure 1. View of collector showing traps, immersion heoters, inlet needle, and necessary accessories
Figure 2. Detail of monifolds and stopcocks showing X625 and MLLIMLL adaptors. All stopcocks are in position A VOL. 36, NO. 2, FEBRUARY 1964
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