Pipette

The pipette (French diminutive of pipe " pipe ", also suction tube, suction or pipette ) is a laboratory device for dispensing liquids. The classic form is a glass tube, which is narrowed at the top and at the other end either open or (eg, a pipette bulb ) is closed by a patch, thick-walled rubber balloon. Frequently, especially in the medical field, also disposable, plastic may be used. Technically complex, the micropipettes described below.

Pipette types

Is on the pipette a volume scale attached, one speaks of a graduated pipette. These are available for full or partial sequence. A pipette that has only one or two brands for a defined volume, ie pipette. Graduated pipettes are suitable for different amounts of liquid and thus more flexible, but also less accurate than volumetric pipettes. Both types are adjusted to pipette liquids with a temperature of 20 ° C and at discharge (Ex. ) are stopping times, if necessary, given the pipettes.

Pasteur pipette from soda- lime glass (ISO 7712) with a volume of 2 ml and a diameter of 7 mm, which is tapered at the bottom, has a long moved out, fine tip of 45 or 120 mm in length and the suction pipe ( length 25 mm) can be provided with a suction cup, or appropriate because of the constriction for cotton plugs. It is used for dropwise dispensing of small volumes of liquid. It does not have any mark indicating the exact volume.

Pasteur pipette, disposable LDPE ( low density polyethylene). Very good reproducibility of the number of drops per milliliter, therefore ideal for distributing aliquot amounts of liquid. These Pasteur pipette can freeze in the filled state, or changed by heat sealing in a closed vessel. The integrated pipetting bulb depresses easily, so minimizing fatigue from frequent pipetting. Resistant to gas or gamma radiation sterilization process.

Scaled " serological " disposable pipettes made ​​of plastic, usually with 5 or 10 ml volume are nowadays used for frequent and simpler dosing as low accuracy requirement and replace the glass pipettes. They are also individually wrapped and available with certified sterility, which simplifies quality assurance in the laboratory.

Some medications (eye, ear, nose drops) filled into the system offered in sealed plastic containers. These containers are pipettes. ( Image )

Drugs pipettes

Pipetting ( pipette filler made ​​of natural rubber f and graduated pipettes)

Disposable plastic pipettes

With a measuring pipette with suction piston suction and discharge take place by means of an above ground-glass piston ( piston pipettor ) with clip.

Micropipettes

A more modern mechanical version is developed by Heinrich Schnitger 1957 microliter or displacement pipette (KHP ), short micropipette. This pipette transfers small volumes from 0.1 ul to 5000 ul accurate than conventional glass pipettes. Piston pipettes operate on the positive displacement principle: A movable piston displaces when pushing the air column beneath it and pulls the air column in the upward movement with upwardly and thereby the liquid to be pipetted into the plugged pipette tip. This pipette tip is disposable plastic, only it comes in contact with the liquid.

-Displacement piston pipettes use special pipette tips with a built-in piston which comes directly in contact with the medium, thus eliminating the air cushion. This pipetting of highly viscous solutions is possible and the accidental transfer of substances in the form of aerosols on the air cushion is excluded.

As with graduated and volumetric pipettes are also piston operated with a fixed volume and piston stroke, which are variable in volume. Here you can set the desired number of microliters by a signal box. You solve the fixed-volume pipettes from visibly. Piston stroke have the advantage of interchangeable plastic pipette tips, making them suitable for work with frequently changing substances or substance concentrations. Electronically controlled piston pipettes are particularly suited for repetitive work, because they relieve the thumb and partly as a hand dispenser (see below) can be used.

Multi-channel pipettes

A particular type of piston pipettes are multichannel pipettes that have 8 or 12 simultaneously operating channels. The channels are ( 12 columns 8 rows ) arranged in a grid of microtiter plates so that they can be edited quickly.

As with the micropipettes with a channel the liquid comes only with the pipette tips ( disposable plastic, missing in the picture ) in contact.

Hand dispenser

Akin to the piston pipettes are hand dispenser, also known under the name Multipette, steppers, Tackers and repeater. These have, instead of the pipette tip, a reservoir direktverdrängendes ( disposable plastic) like a syringe, which allows the recording of a larger volume of a substance, which can then be repeatedly delivered in small increments of the same volume. This in turn allows fast working with microtiter plates or many parallel reaction mixtures (such as in PCR ).

Accuracy classes

The standard sizes of pipettes are listed in the following table. It is divided into two accuracy classes. The pipettes class A the expiration time for the liquid is extended by narrowing the flow peaks, so that already takes place at the glass wall during the course of the dripping of liquid. The error limits of these pipettors meet the requirements of the German Calibration Ordinance. Pipettes class B have significantly shorter run times, but also twice as large error limits as class A. After the expiration of the pipettes class A and B no waiting times are observed.

With improved manufacturing methods to produce pipettes was possible that are within the error limits (Class A) and still have short expiration times. For such pipettes, the Class AS has been introduced. They require, however, after the lapse of a waiting period of 15 seconds. In practice, pipettes, Class AS have strongly enforced and the Class A nearly displaced with longer run times.

Graduated pipettes are also available in three accuracy classes: Class A, Class B and Class AS. For fast running pipettes Class AS A waiting period of 15 seconds after the flow again observed.

Use

Including the liquid was formerly carried out by suction with the mouth in the case of open pipette. Since this can represent a significant health hazard, a pipetting aid must be used. This pipetting the liquid is drawn by dipping the pipette tip. When transporting the liquid, the upper end of an open pipette (generally with the index finger or the patch pipette controller ) must be kept closed. The delivery of the liquid is dependent on the type of pipetting aid. Is certainly the case that after the expiry of 20 seconds to wait, so the remaining liquid may still run. Subsequently, the pipette tip is short strip at the edge of the vessel, as pipettes are calibrated to run (on ' ex '). If using a measuring pipette a portion of the total scale range are used, so a distinction between "forward" - and " Rückwärtspipettieren ". If the substance is precious, or will you save yourself unnecessary work. people will use the "forward " - method. The desired amount of substance is measured at the suction into the pipette and the pipette at your destination completely emptied. As in the pipette tip more substance than stuck in another area of ​​the shaft with the same volume, viscous liquids are pipetted but like "backwards". Here, the liquid is sucked up to the top mark of the pipette, the dosage is based on the scale at the omission. Then the rest of the liquid is again introduced into the storage vessel, whereby the risk of contamination occurs. Since the scale is used opposite in both cases, there are two types of pipettes with scales.

Using a pipette, allows for good control of the amount of liquid, generally a dropwise dosage is possible. Pipettes are among the most accurate volume measuring devices in the laboratory.

Further meaning

In digital image processing, the pipette is a tool with which a color value can be taken from an existing image by clicking with the tip of the pipette on a virtual one pixel. Depending on the program, it is also possible ( eg Adobe Photoshop ) to determine an average of the surrounding pixels.