Transcript
AMERICAN JOURNAL OF CLINICAL PATHOLOGY
Vol. 33, No. 2, February, I960, pp. 152-155 Printed in U.S.A.
MAGNETIC MIXING IN MICROTITRATIONS THOMAS F. O'MARA, B.S., AND WILLARD R. FAULKNER, P H . D . Micro Laboratory, Department of Clinical Pathology, The Cleveland Clinic Foundation, and The Frank E. Bunts Educational Institute, Cleveland, Ohio
Inadequate mixing of small samples of fluid is one of the serious limitations of microtitrations. In sample volumes of less than 1 ml., the ratio of surface tension to
undisturbed. Air-stream mixing also is unsatisfactory, as it produces frothing that obscures the end point and, furthermore, introduces the possibility of error because
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FIG. 1. (left). Photograph of the micromixer with a Gilmont mieroburet; the center well in the Conway unit contains a "microflea." FIG. 2 (right). Photograph of the micromixer with a Scholander type of mieroburet. A Borg microdial is used as a micrometer; a variable transformer is mounted in front.
mass is large. This reduces the turbulence in the fluid which normally can be generated in larger volumes by such means as shaking, rocking, or the passage of air currents. Shaking or rocking of small samples will cause the fluid droplet to move as a unit and will leave the interior of the droplet
of loss of fluid by splashing or by atomization. Magnetic "flea" mixing obviates all of these difficulties and is, therefore, an ideal technic to use for microtitrimetric analyses. This note deals with the construction of 2 magnetic devices and their incorporation with microburets to form complete electrically controlled microtitration assemblies. A general utility magnetic stirring device is also illustrated.
Received, June 24, 1959; accepted for publication October 2. Mr. O'Mara was formerly Micro Chemist, Micro Laboratory. His present address is SouthCONSTRUCTION AND ASSEMBLY side District Hospital, Mesa, Arizona. Dr. Faulkner is Clinical Chemist in charge of the Micro The racks and pinions of discarded microLaboratory. scopes are modified to serve as adjustable152
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FIG. 3 (upper). Schematic half-section (elevation view) to illustrate in detail the micromixer in Figure 1: A—aluminum plate; B—channel Alnico Fmagnet; C—ball bearings; D—shaft fixed to magnet; .E—microscope rack and pinion; F—brass sleeve slotted to fit key, K; G—microscope tube; H— shaft of motor; I—115-v. a.c. induction motor; and /—aluminum support. FIG. 4 (lower). Schematic half-section (elevation view) illustrating in detail the construction of micromixer in Figure 2: A—aluminum plate; B—Alnico V magnet; C—shaft; D—microscope rack and pinion; E— bevel gears; F—115-v. a.c. induction motor; G—aluminum support; and H—ball bearings. 153 Downloaded from https://academic.oup.com/ajcp/article-abstract/33/2/152/1762986/Magnetic-Mixing-in-Microtitrations by guest on 19 September 2017
154
O'MARA AND
height titrating platforms for the 2 instruments illustrated in Figures 1 and 2. Enclosed within the microscope tubes are the shafts of motors to which are attached permanent magnets. Commercially available microburets are incorporated into the stirring design of both instruments. All parts are mounted on heavy aluminum frames, the weight of which aids in reducing extraneous vibrations, as well as providing the necessary rigidity for precise manipulation of the instruments. Figure 3 is a schematic half-section that illustrates the coupling of an induction motor* to a small Alnico magnet. | An aluminum plate (A) is secured to the top of the microscope tube (G). An Alnico magnet (B) is fastened to the shaft (D) which rotates on bearings (C). A brass sleeve (F) is slotted and engages the key (K), and the brass sleeve is attached to the shaft (H) of the induction motor (7). When the microscope tube is raised, the key slides up the slot of the rotating shaft. The induction motor is connected in series with a 50-watt, 1650-ohm rheostat J that permits adequate control of speed. The Gilmont ultramicro buret § used with the model illustrated in Figure 1 was fitted with a ringstand clamp for adjusting the height of its tip from the titrating platform. The motor of the instrument illustrated in Figure 2 is mounted directly to the tube of the rack and pinion of the microscope. Its rotary motion is transmitted through bevel gears to the vertical shaft that carries the magnet. The details of construction are illustrated in Figure 4. An aluminum plate (A) serves as the titrating platform. An * One hundred and ten volt, a.c, 25-watt induction motor, Olson Radio Warehouse of Cleveland, Inc., Cleveland, Ohio. t Channel Horseshoe Alnico V, catalog No. 1948, Arnold Engineering Co., Marengo, Illinois. t Fifty-watt, 1650-ohm rheostat, catalog No. TM 3527, Herbach and Rademan, Inc., 1204 Arch Street, Philadelphia 7, Pennsylvania. § The Emil Greiner Co., 20-26 N. Moore Street, New York, New York. Powerstat, catalog No. S2-001, Type 2, Herbach and Rademan, Inc., 1204 Arch Street, Philadelphia 7, Pennsylvania.
FAULKNER
Vol. S3
FIG. 5. Photograph of the micromixer used with a Schellbach type of microburet. Motor speed is controlled by the variable transformer mounted in front.
Alnico magnet (B) is attached to the shaft (C), which rotates on ball bearings (H). The rotary motion of the motor (F) is transmitted through the bevel gear (E). Motorspeed control is achieved through a small variable transformer. The buret is a modified ScholanderTf design, with a Borg Microdial |[ as a micrometer. A general utility micromixer was designed to be used with the conventional Schellbach type of microburet (Fig. 5). Its titrating platform can be raised and lowered rapidly and easily by means of the rack and pinion, an advantageous feature when a large number of samples are to be titrated. The motor speed is controlled with a variable transformer. "Flea" magnets may be made by means of flame-sealing 5-mm. lengths of paper clip wire in microhematocrit capillary tubes. In order to do this, one end of the capillary If Scholander micrometer burette, catalog No. 3076, Macalaster Bicknell Co., 243 Broadway, Cambridge, Massachusetts. I! Borg Microdial, catalog No. B9-013, Herbach and Rademan, Inc., 1204 Arch Street, Philadelphia 7, Pennsylvania.
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Feb. 1960
MAGNETIC MIXING IN MICKOTITRATIONS
tube is flame-sealed, then the wire is introduced and the tube is cut 2 mm. longer than the wire. The open end of the tube is then flame-sealed while holding the "flea" with forceps. Although glass-covered "fleas" are serviceable, they may leak because of poor seals. Carpenter steel wire,** which is a corrosion-resistant form of magnetic stainless steel, makes a more satisfactory "flea" because it can be used without covering and requires no seals. ** Carpenter Steel Company, Cleveland, Ohio.
SUMMARIO IN
155 INTERLINGUA
Es notate que le utilitate de methodos de microtitration es frequentemente obstruite per le inefncacia del manovras traditional de miscimento quando illos es aplicate a micre quantitates de liquido pro le quales le proportion de tension superficial a massa es grande. Le autores ha solvite iste problema per le insertion in le liquido de un micrissime pecia de metallo que es revestite de vitro e que age como mixtor sub le direction de un magnete. Le construction del apparatura es describite e illustrate in omne su detalios.
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