An Inexpensive Liquid Chromatography Apparatus for Undergraduate Teaching Malcolm McCamish,' G. R. Cannell,2 and L. Bretherton University of Queensland, Brisbane, Australia Analytical and spectroscopic instruments are available commercially, e.g., 60-MHz NMR spectrometers, for use in both routine analyses and undergraduate laboratories. The principles involved can be demonstrated to students when these techniques are an integral part of practical courses and students acquire necessary operational experience. Commercial high-pressure liquid chromatography systems are expensive and, in general, involve a far higher degree of soohistication than is required in an introductorv course. We have developed a low-pressure liquid chromatography pump, slurry filler, stainless steel columns, and injector system suited to an undergraduate laboratory or routine analyses. The pump is of the direct gas displacement type with the flow rate controlled by the & pressure. The apparatus was constructed at minimal cost in the departmental workshop facilities. A commercial UV detector was used with a modified flow cell. Various examples of pneumatic pumps have been described for operation to 5000 psi and as pressurized gas ballast with a piston pump. A potential problem with pneumatic pumps is that eas mav dissolve in the solvent under nressure and he " released at the low pressure end of the column or in the detector cell. We have used a double acting PTFE oiston sealine against the solvent and the gas on the pump surfaces tominimize this problem.
The slurry filler is a stainless steel cylinder 4.5-cm I. D., 5.1-cm 0. D. and 50 cm long, fitted with stainless steel end caps, the lower one having an internal taper. Pressure is applied directly from a nitrogen cylinder at 1000 psi. The column to be packed,whether analytical or preparative, threads directly into the filler. A small bleed hole is drilled in the top end cap gas connector to allow nitrogen - gas . to be released slowlv when column packing is completed. All columns taper at the outlet, and the preparative columns are tapered on the inlet also to enable a more uniform concentration of the zone when the substrate is injected on the column. As shown in Figure 2, the preparative columns (length 30
cm,I.D.2.5cm,O.D.3.14cm) are built with a raised flattened section (1) to facilitate removal of the end caps (2). Swagelok fittings (3) are packed with machined PTFE with a 1-mm hole to eliminate dead soace. The PTFE is extended o n the face of the Swaeelok to obtain a leakproof seal T o retain the column packing, we use filter paper discs supported by several discs of stainless steel gauze (4). Glass sinters lack the necessary mechanical strength and stainless steel frits tend to clog with fines with the packing used. With analytical columns of 0.8-cm I. D. and 1.12-cm 0. D. (length 15-60 cm), Swagelok fittings are connected directly to the outlet (5) with the inlet joined to the injector. Smaller columns of 0.37-cm I. D. and 0.6-cm 0. D. are comoatihle directlv with
Description The pump, represented sectionally in Figure 1,can be operated to 250 psi. I t consists of a stainless steel cvlinder (maximum rated pressure 900 psi at 2 5 T ) 63 cm long &th 7.5 cm 0. D. and 6.9 cm I. D. (1).End caps (2) of stainless steel are threaded and sealed to the ends of the tube with PTFE gaskets. 'The inner surface of the cylinder is polished. The oiston
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piston rod against the vertical scale (5) mounted on the hack of the pump. Nitrogen gas from the cylinder regulator is introduced to a miniature pressure regulator (6) with a gauge to set the pump pressure. The valve (7) can he used to isolate the pump from the gas supply, but it is not essential for operation. An exhaustine solenoid valve ( 8 ) is onerated bv a microswitch (9) to release the gas pressure in the pump &d close off the ras inlet. An adiustable stop (10) on the oiston rod activatesihe switch allowing the voGme of solvent to be pre-set. For stability, the punip is mounted on a h e a w stand. T o fill the pump, the piston is forced to the bottom of its stroke to remove trapped air or solvent. Vacuum is then applied to valve (11) while valve (12) is open to the solvent reservoir. A one-way valve (13) prevents air or solvent from being introduced from the solvent outlet line. Valves (11) and (12) are then closed, and gas is introduced by the solenoid (8). The pressure is set on the pressure regulator manually or by the adjustable stop.
Presented in part at the 10th lnternatlonal Symposium on Chromatography and Eiectrophoresls. Venlce, Italy. 19-20th June 1979. Author to whom all correspondence should be sent. Present address: Conjoint Internal Medicine Laboratory, Royal Brisbane Hospital. Brisbane. Australia.
umnsare recessed to house the filter paperlgauze assembly. Figure 1. Sectional diagram of the pump.
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=s* Figure 2.
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Construction diagram of the preparative columns. Volume 59
Number 3
March 1982
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249
Samples are introduced via septum seal injection. Samples are injected on column via a 1-mm hole. With the preparative columns, a silica gel pre-filter is built into the injector block. A Cecil instrument variable wavelength UV monitor (model CE212) is used with modified flow cells a s a detector. The cells are constructed from a stainless steel rod to allow for varying internal cawacitv. construction is the machining of the stainless steel cylinder which may not in fact be necessarv. This reauires workshow facilities no more sophisticated than a lathe: We now have several of these units operating in our department. The total cost of material for the most recently constructed was less than $(Aust) 250 for the pump and $(Aust) 50 for the slurry filler. Since labor costs were less than $250, this means that the unit is operational for atotal outlay of ~ $ 5 5 0 . Results and Discussion High-performance liquid chromatography for maximum efficiency utilizes packings of uniform mesh size. Many separations, however, can be successfully effected using thin-layer chromatography silica gel.
250
Journal of Chemical Education
Compounds separable using silica gel as adsorbent with this equipment include structural isomers (e.e.. o-. m-. and w.
fumarate), aromatin (e.g., benzene, naphthalene, anthracene), " l ~ c ~ ~ ~ ~ ~ ~( #l.g., c , gprt,g%tcc
