Versatile Peristaltic Action Micropump Paul B. Hamilton, Alfred 1.
du Pont Institute of the Nernours Foundation, Wilrnington 99,Del.
T
pump described by Solandt and Robinson [J. Sci. In&. 15, 268 (1938)] for use in physiological laboratories is based on the milking-tube or peristaltic-type action. Their design incorporated two pump units on the same shaft to ensure volumetrically equal exchange of blood, in either direction, independent of relative blood pressures, when two animals were being cross-circulated. The pump delivered from 15 to 30 liters per hour and ITas used a t pressures up to approsimately 3 p.s.i. The need for a laboratory micropump capable of accurately metering small volumes of fluid a t moderate pressures and a t lower flow rates than those delivered by most commercial pumps, led to modifications of this pump. The double pump feature nas retained. and improvements in constructional details added to the strength and dependability of the apparatus. A continuously variable speed reducer which provides precise control of the mechanical power has been incorporated in the mechanical drive (suggested by R. E. Haist, Department of Physiology, University of Toronto, Toronto, Canada). The changes produced a pump capable of delivering fluids a t rates from 1 to 122 ml. per hour a t pressures ranging from atmospheric to 35 p.s.i. Flow rate is continuously variable and readily adjusted between these limits, and the volume delivered is constant to within d=l% a t settings of 1, 4, 12, 25, and 35 ml. per hour. The performance should be as good a t higher flows. Two pumps of this design, which have been in constant use in the writer's laboratory for 3 years, have proved versatile and very dependable. They supplied protein solutions to papercurtain electrophoretic assemblies a t 1 ml. per hour and influent buffer solutions to ion exchange columns a t 4 to 35 ml. per hour. HE
The essential construction features are illustrated in Figure 1. The two pump sections, P1 and P2, are brass cups (21/2inches in inside diameter, 3 inches in outside diameter, and inch in inside depth) which are keyed, K , to the aluminum alloy (24ST) frame, F . Mounted on the central shaft, S, are two roller assemblies, R1 and R2, n-hich revolve inside each cup. By turning the knurled nut of the roller adjusting screr, M , the roller is advanced t o the periphery of the cup t o compress the rubber tubing: The adjusting screw is locked in position by a knurled locknut, N . The roller is mounted 011 its shaft,
RS, through the needle bearings, RB (B-44, The Torrington Co., Torrington, Conn.): The shaft itself is steel, tempered to a hardness of Rockwell C45 to 50. The shaft is fitted to a U-shaped slide piece, SP, of l/c-inch brass, each arm of which slides in corresponding grooves on either side of a stainless steel slide block, SB. The slide block is locked to the central shaft by a setscrew. The crossmember, which bears the roller adjusting screw, is bolted to the ends of the U-shaped slide piece. The roller adjusting screw terminates in a slot which is engaged inside the slide block by the vertical lockscrew, L . The roller assemblies are mounted 180' apart to minimize bending of the shaft when both sections of the pump are in operation. The central vertical shaft of stainless steel and 6/le inch in diameter rests a t the bottom in a thrust bearing, T B (No. 1602 DS Torrington), housed in a brass retainer, H . The shaft is rotated by the bevel gear assembly, BG (G-487, bronze, 2 to 1 ratio, Boston Gear Works, Boston, Ilass.). The pinion shaft, PS, of the gear connects through the multijawed coupling, D (FA-75, Boston Gear), to the output shaft of a suitable speed reductor. A ll,,- or llI5-hm alternating current . -motor,-- 1725 to 1800 r.pm.-e.g., Model KO. 5KH25 AC393, General Electric Co.-n-hich sumlies mechanical power is connected-by a No. 2 flexible coupling (Lord Mfg. Co., Erie, Pa.) to the input shaft of a Zero-Max I
S C A L E : INCHES 0
1
2
3
4
SB SP
RS
RB
Figure 1.
Peristaltic action micropump
continuously variable speed reducer (Standard Model No. 14, 18, or 142X with screw control, Revco Inc., 1900 Lyndale Ave., South, Minneapolis, Minn,). The output shaft of the ZeroMax is connected to the input shaft of a 300: 1 speed reductor (Model LK9, Boston Gear Works, Quincy 71, Mass.) by a S o . 2 flexible coupling (Lord). The output shaft of the reductor is joined to the pinion shaft of the pump through the multijawed coupling, the pump half of which is shown a t D. The motor, variable speed reducer, reductor, and pump are all mounted on an 8 X 24 X '/: inch 24ST aluminuni alloy base. Vibration of the unit in operation is minimal, but it can readily be damped out by placing on foam rubber. Softfles rubber tubing, T (Dynalab Corp., 850 Clinton Ave., South, Rochester 1, S . Y.), l/g inch in inside diameter, and inch in wall thickness, was superior to several other tubings because of its resilience and resistance to abrasion. To install the tubing, one end, moistened with glycerol, is pulled into the cup through port A and after making a single turn is pulled out through port B. The tubing should be installed without tvist so that the loop inside the cup lies flat. T o prevent creeping, the tubing is held firmly but without constriction in retaining clamps which rest on small brackets affixed to the frame: The positions of the clamps are indicated schematically a t C, C. K i t h the roller assembly loosened, the pump line can conveniently be filled with fluid and all air bubbles displaced. The roller adjusting screw is then turned to compress the tubing and tightened sufficiently to ensure that the lumens of both portions of the tube are completely closed by the roller when i t passes the point of crossover between d4 and B. Once installed, further lubrication of the surface of the tubing is never necessary. The approximate volume delivery can be computed. The maximum output speed of the Zero-Max reducer with 1800-r.p.m. input is 450 r.p.m. This speed is reduced by the 300:l reductor and the 2 : 1 bevel gears to give the vertical shaft, S,and hence the rollers. a velocity around the cup of 43 r.p.11. Assuming the center of the tube lumen t o lie inch inside the cup, the volunie displaced by milking action for one revolution of the roller is approximately 1.42 ml. Hence, maximum volume output will be 61 ml. per hour. Adjustment of the Zero-Mas screw control t o give rotational speeds of less than 450 r.p.m. will reduce the volume delivered, and this may be decreased t o zcro. To obtain greater adjustment a t VOL. 30,
NO. 5 , M A Y 1958
1017
low flows, a 600:l or 9OO:l reductor may be substituted for the 300:l unit suggested. For flow rates greater than 61 ml. per hour, the input and output tubes of the two pump sections are joined in parallel: this doubles the output to give a maximum dplivery of 122 ml. per hour. It is unnecessary to apply any pressure head a t the intake; when operating properly, negative pressure developed in the intake will support a t least 25 inches of mercury. The pump may he
operated for relatively long periods: The maximum continuous run in this laboratory was 14 days. The maximum pressure developed before ballooning of the Softfles rubber tubing varied beh e e n 35 and 40 p.s.i.: This maximum depends on the properties of the individual piece of tubing. KO difficulty was encountered when the pump was operated continuously between 30 and 35 p.s.i. Depending upon the amount of use and the conditions of operation, the tubing had t o be replaced every 6 to
12 months. At the higher operating pressures, abrasion was more rapid. Mechanical drawings with all constructional details are available on request. ACKNOWLEDGMENT
The author gratefully acknowledges the assistance of E. G. Rohrbaugh, Model Machine Co., 1129 Capitol Trail, Sewark, Del., in improving the design of the apparatus as well as his able fabrication and assembly of the unit.
Polarography at Very Negative Potentials. Improvement of Polarograms by Use of N,N-Dimethylformamide and Tetrabutylammonium Iodide Frank L. Lambert, Occidental College, Los Angeles, Calif.
involving D polarography - an investigation of organic halogen URIVG
compounds whose half-wave potentials were of the order of -2.0 to -2.5 volts, N,i\i-dimethylformamide (DlIF) was found to be superior solvent in such negative regions. Although D l I F has been used as a solvent in the polarography of aromatic hydrocarbons (1, 5, 6),its outstanding characteristics in overcoming some polarographic difficulties have not been fully described. A major problem in the polarography of any organic compound a t very negative potentials is the erratic and variable rate of formation of the mercury drops. This results in irregular current surges and makes an automatically recorded polarogram difficult or impossible to read. Older work a t these potentials, in which manual polarographic equipment was used, appears overly accurate because the reported averages of a few galvanometer swings do not reveal the large number of unusual mercury drops. In aqueous alcoholic solutions, these erratic drops can be seen to be caused by formation of gas inside the capillary a few millimeters from the tip. The small bubbles of gas may be hydrogen produced by reduction of water or alcohol adsorbed on the sides of the capillary. As the bubbles grow larger and move toward the orifice, a mercury drop is forced to fall before it is completely formed. A sudden decrease in the current is recorded. A bubble arriving a t the orifice a t the time a drop is to fall causes an excess of mercury to be included in the drop and thereby produces a sudden rise in the recorded current. Very slight imperfections in the envelope of the recorded polarogram, in contrast to the gross effects of erratic drops, probably result from traces of solid or slightly soluble liquid a t the immediate tip of the capillary. These 1018
ANALYTICAL CHEMISTRY
materials cause the drop to fall a few milliseconds too soon or late, but such imperfections are objectionable only in very precise work. Capillaries can be readily cleaned to prevent such erratic or variable drops ( 3 ) , but recleaning was frequently necessary in the aqueous alcoholic solvents used by the author prior to adoption of anhydrous DMF. Because methanol is a relatively strong acid (21, common use of methanol-water for polarography of difficultly reducible organic halogen compounds is inadvisable. Traces of methanol surge into the capillary after each drop and are reduced more readily than nater a t very negative potentials. Aqueous ethanol is superior in its lesser tendency to yield ragged polarograms, perhaps because ethanol is a weaker acid than water. Absolute ethanol would be excellent except for the high resistance of such solutions. Methanol-benzene solutions and Cellosolve show very high maxima using tetrabutylammonium iodide as the supporting electrolyte with organic halogen compounds, although they are satisfactory solvent systems for polarography of other organic compounds. Dioxane-water is an excellent solvent for the reduction of organic halides, but the author found it difficult to purify and preserve. Thus, it is not desirable for routine work or for research if time is limited. Anhydrous DAIF is easily purified by distillation through a %foot helixfilled column. The middle portion of the distillate from pure DMF is the fraction saved. No change occurs on storage a t ordinary temperatures for a t least 1 month. If tetrabutylammonium iodide is used as the supporting electrolyte a t concentrations of 0.1 to 0.2M, the resistance of a n ordinary mercury pool cell is less than 1000 ohms. The major reasons for recom-
mending DXF with tetrabutylammonium iodide for polarography a t negative potentials are that very few erratic drops occur, no slight imperfections in the envelope of the polarographic curve can be noted, and the capillary stays clean for months if it is stored in pure D1IF. In addition, no maxima were observed with low concentrations of the many aliphatic and aromatic halogen compounds tested and therefore no inhibitors were needed. Other alkylammonium electrolytes, such as tetraethylammonium bromide, yield slightly uneven current retords in DlIF as compared to tetrabutylammonium iodide: However, the polarograms are completely readable, in contrast to the illegible results at very negative potentials in aqueous methanol or ethanol. Lambert and Kobayashi (4) found that tetraethylammonium bromide reveals a wave for chlorobenzene which is not obtainable with tetrabutylammonium iodide. The latter electrolyte is still preferred for most work a t -2.0 to -2.5 volts because of the smooth records it gives in DMF.
LITERATURE CITED
(1) Edsberg, R. L., Eichlin, D., Garis, J. L., ANAL.CHEX.25. 798 (1953). (2) Hine, J., Hine, E., J . Am. Chem. SOC. 74, 5266 (1952). (3) Lambert, F. L., Chemist Analyst 469 10 (1957). (4) Lambert, F. L., Kobayashi, Kunio, J . Org. Chem., in press. (5) Wawzonek, S., Berkey, R., Blaha, E. W., Runner, M. E., J . Electrochem. SOC.103, 456 (1956). (6) Wawzonek, S., Blaha, E. mi.,Berkey, R., Runner, M. E., Ibid., 102, 235 (1955). WORKsupported by a grant-in-aid from the Research Corp.
