US2376231A - Pipette - Google Patents

Description

, PIPETTE Filed Feb. 12, 1942 fui-Zz/enfor V VAa, VWM v figo/zaga Patented May 15, 1945 PIPETTE Davia J. conn, chicagc, 111., Applicatie kFebrum1.y.12, 1942-, serial No. 436,535:

2Claims.l (c1. zzz-m).

The invention relates-to pipetteS of theA type used in chemical orbiologicallaboratory'work.

The general object of theinventionis.toprovide a pipette of such inexpensive;construction that it may be used once and. then thrown away..

Anothergeneral object is to provide a; pipettev of inexpensive construction; so that it need not be used more tharronce', and; offlsuch accuracy that itis equivalent` to or'even better than the present pipettes made Yofglass. f

More specifically, it; .1s

parent material formedA on a mandrel to provide an inner bore. of uniformudiameter an'dsuitably Vreenforced at such "places, particularly'the ends, wherev the flexibility of the transparentvmaterial would-be undesirable. f

Other objects and advantages will parent from the following description, taken, in connection with thel accompanying drawing, in whichlk; y

Figure l is a perspective view of a pipette-embodying; the features of the invention.'A

Fig. 2 isy anf enlarged longitudinal sectional View? of the pipette shc` wninFig.,1xv f,

Fig.. 3 isra. perspectiveview of the plug utilized in. theupper' end of the pipette.

Figi 4v is a. perspectiveview ofthe plug used in the lower end of the pipette.

Fig. 5 is a longitudinalisectional view of a modiiedform of pipette.

Fig.; 6. isaperspective view of aplug'used in the lower end: of thepipetteshown. in Fig. 5;

other-modied formof pipette. y l Fig. 8 is an end View of thelowery or tip end of the pipette shown in Fig. 7. I

Pipettesv employed in chemical and 'biological' work comprise elongated tubes'- of predetermined capacity and are used for drawing off ameasuredquantity of liquid from a vessel containing `a become ap- .an objectv to providef a. pipette comprising a'tubeof substantially'trarrsf larger quantity. Heretofore pipettes have usually been made offglasstubing having relatively thick walls. The lower end, or the'end adapted to be placed in the vessel .containing the liquid, is usually drawn or beveled'down toa'` reduced diameter so that the; bore 'therethrough is substantially less thany the internal diameter of thetube itself; The liquidi is drawn intofthe pipette byV placing the upper end inv thefusers mouthand'sucking up.on.-`1t.,` The; upper. end; ofthe ypipette then is closed. byf placing. the iingerfthereon and the relativelyi small diameter.I ofy thef passage through-` the lowenemi prevents any-ot the liquid from vrun-r ning! eutiofi therpipette. The shape of.' the! lowerl wf end also facilitates` the formation of drops-when the upper end is kslightly loperrtol permit airto` enter the interior of the pipette. l

Greatcare must be exercisedA in the manufs'icz-v ture of -pipettes in order to produce a relatively' uniform insidediameter topermit rneasuren'l/entKV of the ,contents by the uniform applicationof..

graduated indicia onthe outersurface .of 'thef' In the case of glass pipettes, "biecauselolf,`

the inabilityy to obtain exact uniformityl ,bei-.weengvv different ltipettesyeach pipette of high grade must be individually` calibrated'. Also, with ag lass.

pipette, the'meniscus of the liquid/be. it concave or convex, is relatively large so; vthat. there` is! chance of error in the measurement of. the liquid.

drawn intothepipette., n

Because of the difficultiesinvolved. ingmaking an accurate pipette, the expense thereof isrela-- tivelyA high. ,Thus it is necessary-'to` use* suche' f pipettes over and-over again with met-iculo.us-carev exercised in the'cleansing of each pipette after:l

use. Such cleansing` involves placing each pipette:

in an acid or alkaline solution with thorough sub;- sequent rinsing and drying. For bacteriologicah and `seriological work the pipette must' bethor-v oughly sterilized and. then perhaps carefully wrapped` to avoid contamination. Not only is:l this an expensive procedure from the standpoint;

of theL labor involved,l butl also. from. the standpoint of the-chemicals used in theacid or alkaline solution. In fact, under present conditions'pro' duced by the war, some` of these chemicals ftl'iatfv have` heretofore been commorly used are now'k almost impossible to obtain. l

In using pipettes for certainy work, the upper'v end. of each pipette -is packed with a cotton filter to prevent passage of bacteria eitherv from-thel mouth of thefuser into the liquid in the-pipette' or from the liquid into the mouth of the user. Thus before cleansing and sterilizing a glass pipette, the cotton filterhas to'b'e-withdrawn andz before the next usea new iilter'inserted.

As mentioned above, the principal object ofthe present invention is to'provide a pipette whichis soinexpensive to manufacture that it may bez used once and then thrown away; Thus many'V of the disadvantages and difficulties occurring. with the-use of glass pipettes are pbv'ously avoided. I have found thai; a thin-walled tube; made of inexpensive-plastic material which is substantially transparent is suitable.` A materialA` of this character which isv commonly known .by the." trade-mark. C'ellophane may be 4ei'rrployed for V thispurpcse; anda pipettefmade thereof maybe as accurate as a glass pipette, or even more so, as Well as provide a number of other advantages.

The tube is preferably formed in the manner usually employed in making Cellophane tubes, that is, by wrapping a relatively narrow strip of Cellophane of uniform thickness helically around a mandrel and simultaneously causing the edges of the strip to adhere to each other. The mandrel maintains an unvarying internal diameter and the tension on the strip as it is being wound is maintained constant so that the resultant tubes are extremely uniform throughout their length. Cellophane has the advantages of not being read- `ily attacked by chemicals, of being transparent,

and of being materially unaffected by temperatures up to 110 to 120 centigrade, which temperatures are suflicient-l for sterilization. It is also nonbreakable, light in weight, and as mentioned above, inexpensive. A further advantage has been noted in its use in that many of the liquids encountered in routine hospital work do not form such an accentuated meniscus in a Cellophane tube as in a glass tube, so that an accurate determination of the level of liquid in a Cellophane pipette can be more easily made than in a glass i pipette.

In the preferred form of the device shown in Figs. 1 to 4, inclusive, the pipette comprises an elongated tubular body I made of Cellophane in the manner above described. Since a thinwalled Cellophane tube of this character is to some extent yieldable, those portions of the tube, particularly the lower end or tip, which' are subjected to forces capable of distorting the tube are preferably reenforced. Thus in the lower end of the tube I provide in the preferred form a tip Il adapted to fit snugly within the tube. To insure a tight fit, advantage is taken of the pliable and resilient character of the plastic material, the diameter of the tip being such that it will be frictionally retained within the tube without the necessity of providing any particular fastening means. In the preferred form the tip II has an upper portion within the tube and a slightly larger lower portion vI2 providing a shoulder I3 adapted to abut against the end of the tube.

Since it is desired to retain liquid within the pipette merely by sealing the upper end thereof, the tip II is provided with a passage I4 which is relatively smaller in diameter than the internal diameter of the tube so that air cannot creep into the tube through the passage I4 when there is liquid therein. The passage I4 should also be formed so that the liquid can be permitted to pass out of the pipette in a smooth'strearn when desired, 0r to facilitate the formation of drops when small amounts of air are permitted to enter the top of the pipette. To this end, the passage I4 is of substantial length and the lower end of the plug is externally beveled or partially tapered as at I5. In the preferred form, the bore I4 is preferably centrally located in the tip. The upper end of the tip may be dished as at I 6 to facilitate complete drainage. The tip II thus reenforces the tube, provides a proper vent therefor and furnishes a solid end to prevent distortion 0f the tube when pressed against an object.

In the upper end of the tube I also reenforce the tube by providing a top member 2 i3. The top member 20 is preferably frictionally retained within the Cellophane tube, as in the case of the lower tip II, the lower end of the top member 2li being slightly tapered as at 2| to facilitate insertion, and the upper portion of the top member having a tight lit within the tube. The top member 20 preferably has its upper end flush with the upper end of the tube. To permit the passage of air into and out of the tube, the top member 20 is vented as by a central aperture 22. This aperture is substantially smaller than the outside diameter of the top member so that the end face of the member in itself and with the end edge of the Cellophane tube provides a relatively large flat surface against which the finger may be placed to effectively seal the aperture after liquid is drawn into the tube.

The top member 2U is also constructed so that it may carry a cotton filter. Thus the cotton filter may be inserted, during manufacture, directly into the member rather than having to insert it rst into the tube. To this end the member is cupped, as at 23, with the cupped portion opening inwardly of the tube. The cotton filter, indicated at 24, may then be packed in the member 20 prior to insertion of the member in the tube.

The members I I and 20 may be made of any rigid material resistant to acid or alkaline liquids, and capable of being formed either by cutting or molding. Thus the members may be made of molded ceramic material, or preferably are made of plastic molded material such as Lucite.

The exterior of the tube may be marked with suitable graduated indicia 25 similar to those utilized on a glass pipette. However, the indicia may be placed thereon by surface application such as ink or paint suiicient for one-time use, and would not have to be etched into the material as in the case of the glass pipette. Because of the accuracy maintained for the internal diameter of such Cellophane tubes and the uniformity of thickness of the material, the tubes do not have to be individually calibrated and the location of the indicia on one tube of a given size will be exactly the same as on another.

A pipette of this construction may be sterilized and wrapped as a part of its manufacture. Also,

, the cotton lter 24 may be inserted in the top member 20 as a part thereof. Such pipettes may therefore be supplied to the laboratory ready for use without any doubt as to their sterile condition, or whether there is any foreign residue left in the pipette from its last use or from a cleansing process.

In the modified construction shown in Fig. 5, the Cellophane tube and the indicia thereon are of the same character as in the prefered form. The members in the respective ends thereof, however, are of less expensive construction. Thus each member comprises a piece cut from a cylindrical bar and provided with a longitudinal groove 3D along one side thereof. The groove 30 may be milled into a long rod from whichthe pieces are cut and is preferably of rounded form, as is apparent from Fig. 6. The grooves 3U, together with the adjacent portions of the tube, provide suitable vents at the top and bottom of the tube. The tip member, in order to facilitate proper iiow therethrough, may be cut at an angle, as indicated at 3|, sloping outwardly toward the side of the member` in which the groove 30 is located. Such a construction is obviously very inexpensive since these members may be readily formed from a long rod of the material with only slight machining operations to properly shape them.

In the modified form shown in Fig. 7, the Cellophane tube is also of the same construction as in the preferred form. However, the upper end of the tube is reenforced by a top member of a substantial length so that'not only is the end portion reenforced but the portion there- -below which is usually grasped in handling the pipette is 'also reenforccd. To this end yI rprovide a top member comprising a sleeve `32 of Cellophane, oiled paper, or the like, having an external diameter fittingl snugly within the end of the tube. The lsleeve 32 extends well down into the tube, say for two or two and one-half inches, and thus'makes the tube rigid for the length of the sleeve. The bore of the sleeve is such as to permit the proper flow of air intofand out of the tube, While the end edge of the sleeve together with the end edge of the tube, provides a flat area surrounding the bore and facilitates sealing of the bore when the finger is placed thereover. In the lower end of the pipette I may provide a tip 33 comprising'a piece cut from a cylindrical rod or bar and having one side thereof cut fiat as at 34 to provide a suitable passage between the tip and the Cellophane tube. The lower end of the tipp is preferably cut at an angle, as indicated at r35, slopingoutwardly toward the fiat side 34. The flattened side 34 may be formed either by milling or by mere abrading so that the manufacture thereof glass pipettes now available `because of the in` herent accuracy resulting from the manufacture l. A pipette comprising a tube made of a thin y ilexible strip of a cellulose plastic material helicallywrapped to a uniform diameter,`and members in the respective ends of said tube to re-` enforce the tube atl the ends, the member at the lower end being provided with an elongated passage of substantially smaller diameter than the internal diameter of the tube for regulating the flow from thetube, and the member at the upper end being vented to permit passage of air into or'out of the tube and having an end surface cooperating with the end surface of the tube'to provide a relatively at area surrounding the vent, whereby the vent may be readily sealed by `placing the finger thereover.

2. A pipetteconsisting of a tube composed of a thin flexible strip of a, cellulose plastic material helically wrapped to a uniform internal diameter, and a tip member having a cylindrical portion in tightly fitting relation to thelower end'of the tube and providing an elongated passage of a diameter substantially smaller than the internal diameter of the tubefor the discharge of uid from the tube, the upper end of the tube being'. constructed so as to be sealed by placing the linger thereover, and a calibrated scale printed directly on the tube.

DAVID J. coHN.

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