Chemical Instrumentation S. 2.
LEWIN, N e w York University, Washington Squore, N e w York 3, N. Y.
T h i s series of articles presents a surveu chararteristics, and limitations of those instrnments applirntions i n chemical work. The emphasis is on equipment. and approemate prices are quoted to show of cost of t h t'arious ~ tupes of design and construction.
of the basic principles, which jind inzporfant cmnmerciall~/available the order of nzngnitzcde
14. Chromatographic Equipment .
, 1he efferts of solvent evaporation from the free surfaces of a paper or gel elertrophoreeis support due t,o the heating proclurcrl by the flon of current can be eliminated by clamping the sheet or bed between glass or plastic plates. This a p pronrh t o supported electrophoresis has hem adopted in the instrumentation designrd by E. C. .4pparstus Co., Swarthmore, Pennsylvnnin. Figure 48 shows a
(concluded)
viously described, the paper rests on a wabcr-cooled tshle for removal of the elertricsl heat,. The K C . apparatus differs in that the water-cooled srrfnrr rompletely surrounds the elrrtrophort~sismedium.
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coil. imbedded'in the ploatic confining p1oter referred to in Figure 48 con be reen.
Figure 48. Diagram of the EC Apporotvr Co. Vertical Gel Electrophoresis Apporotus. The upper and lower electrode comportments are shown; buffer mlution contacts the upper ond lower ends of the gel block shown in the onnvior channel between plartic confining plates. There plates are cooled b y imbedded water coils lnot shown).
schematic diagram of the EC470 Vertiral (;el Elect,ropharesis Apparatus ($325), and Figure 49 s h o w thc actual appearance of the instrument. I n this device, which is intended primarily for use with gels, the medium is contained hetm-een non-wetting, non-condurtive plastic surfaces; these surfaces are the hounding planes of strut.. tures which contain imbedded tubing through whirh rooling water continually riwulates. This arrangement prevents evsooration bv . (1) . . .nravidine n ohvsicsl barrier t o the esrape of vapor molecules, and (2) rondurting elertriral heat sway as rapidly as i t is gmerated. I n several of the paper dwtrophorrsii; devires pre-
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Becalse the medium is support,ed on both sides, this appllaratm ran be used eauallv " well in the vertical and horizontal positions. The b u f f ~ compartments r are physicslly separate, and elcctriral eommunication hetu-een the elertrodcs in these chambers ran only occur dong tho psth provided by the electrophoresis medium. The elertrodes consist of &tinum wires ~ t r e t ~ h e between d opposing wr.alln in the hoKw campartment,~. This company also makes a n apparatus designed for us^. with either paper or a gel (Model EC155, complcto with 1000 v, 200 me, power supply, $545). If paper is t o he used, it. is placed between plastic insulating shields, a ruhher pad is added, and the combination is rompresscd hetween ,rater cooled plnrtie plates.
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High V o l t a g e P h e r o g r a p h s Electrophoresis wibh high potcntinl gradients applipd to the medium has the advantage that the electromigration m n h~ mad? t o nreur with s u f f i r i d rapidity
feature
t h a t tho separation of t a o component,^ having slightly diferent mobilities is not disturbed by the random diffusional sprpading out that orrurs %?-henprolonged runs are neressnry. Thus, in many cases t,he ~harpness of sepnmtions can ho markedly improved hp opwating a t high npplid voltages. However, the success of such proc~durrsdepends largely upon t,he effeetivenrns of the means employed for conducting a v a y the heat generated by th? pnssngr of current. Since the p o x w dissipated hy the electricity iincresses as t h ~square of the voltage a t constant. resistanre ( P = E 2 / R ) , the rffirirnry of the- rooling is of critical import,anrr in this type of instrmnmt. Two instrntnent~ speeifiesrlly designed for high voltage pnpw elwtrophoresis are made by Gilson Medical Electronics, Middleton, n-isransin. The hlodd M Electrophorator ($4800) contains a refrigerated rlertropharctir platform, cooled by the fluid c i r r n l a t ~ dfrom s l-hp rcfrigcrstor. A glass plate covered with a thin Teflon membrane lips on this rpfrigrratcd platform, and the paper strips or shcet lie on the Teflon. Thp rhambrr covw has a polythylenp membrane mountrd below it,s lower rurfare, ir-ith an air spare betaern the membrane nnd the rover. If air pressure is applied, the polyethylene is pressed against the paper strip, uniformly compressing i t against the refrigerated Tcflon surfsee, and insuring gond rooling. If the air pressure is reduced below atmospheric pressure, the polyethylene membrane is sucked up, forming a. shallom- rhamber above thep a p q this is done whenever i t is neressary t o facilitate moisture equilibration. The power supply delivers up t o 20,000 v and 50 ma. The UME Model D elertrophorator ($1950) employs a power mpply t,hat ddivrrs up t o 5000 v a t 300 ma. Filter paper sheets up t o 18' X 22" are immersed in a fihcrglaas bank containing a light petroleum oil (Varsol, available from Standard Oil Company of W e x Jersey). Stainless steel coils through a h i r h cold t s p water circulates are mounted in the oil a t the top of the tank, and serve to remove the heat transmitted t o the oil from t h PBPPL ~ A high voltage paper ~lectrophort.~iz unit is also availahlr from Hhandon Srientifir Co., London (US. distributor: Consolidated Lnhoratori~s,Inc., Chicago Hcights, Illinois: price: about $2100). The power supply delivers up t o 10,000 v a t 100 ma. Thc paper is sandwiched between polyethylene sheets, and upper and lower waterrooled platens are pressed against hoth sides of this sandwich by thr application of air pressure. ~ ~ l ~ , , ,~, ,
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Instruments designed for dertrophorrsii t,hrough a packed adsorbent eolumn arc
Volume 38, Number 1 1 , November 1961
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made h y LKB-Frodukter AB, S w d e n LKB Instruments, Inc., Washington 14, D. C.). The Column Electrophoresis Apparatus (Mndrl R340C with 1200 V, M ma. powrr supply, $725) consists of a 280-ml colonm tub?, which communicates with anode and cathode vesads conhining platinum r1c.cbrodes, and the tubing, vessels, and fittings ncrassarv for the charging of the e
thc l i ~ h tintm8itiw fdling w tlw twn p h ~ l ~ r d lTtw ~ . position of lhc lwmn A flwtor is l l ) :L~ n~~ m s u r ~ of! l l wfrtwtivc ~ indm of t,Iw smnplc Sinw this is (Iircctl? coupled to the recorder pen, l h r recorder iiuliwtcs d!Y,iirwt,ly. Scnsitivit,ics :is grmt IW =ti X 1 0 in
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Journal of Chemical Education
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