Pipetting aid
As Pipetting devices are referred, which use the measuring liquid quantities or instead of glass pipettes in a laboratory allow or facilitate.
In the past, oral aspiration of pipettes was only used for liquids whose vapor inhalation , accidental aspiration into the oral cavity and swallowing could not lead to health damage, with volumetric pipettes and graduated pipettes mostly with pipetting aids. The German Social Accident Insurance now generally forbids sucking in pipettes by mouth in Germany .
Depending on the area of application, a wide variety of shapes and materials have been established for pipetting aids. In addition to rubber polymers , silicone is also often used as a material for pipetting aids due to its very good chemical and mechanical properties.
Peleus ball
A typical Peleus ball has three valves for the following functions:
- Valve A (from outlet) above: press air out of the ball (to be able to suck in with the ball later)
- Valve S (from suction) below: draw in liquid medium into the pipette
- Valve E (from emptying) on the side: dispense pipette contents in a controlled manner
application
First, the Peleus ball is placed on the pipette. Everything else can be done with just one hand. Open valve A by gently squeezing it and press the air out of the rubber ball. If you close valve A (release), the restoring force creates a negative pressure with which liquid can be sucked in. The aspiration is carried out by squeezing the valve S in a controlled manner and the liquid is drained off by pressing E. If a large volumetric pipette is used, it may be necessary to repeat the entire process to aspirate the entire volume.
Experienced users can also use a peleus ball to quickly empty a pipette (for example, to add reagent to a flask as quickly as possible); for this purpose, the pipette neck is fixed in the peleus ball with the ring finger to prevent it from slipping out, valve S is opened with the pressure of the middle finger against the ball of the thumb while the thumb and forefinger are pressed (or the fingers of the other hand) push the ball.
inventor
The inventor was Friedrich Pels Leusden, Hygiene Institute of the University of Kiel, (should not be confused with the surgeon of the same name, Friedrich Pels Leusden ). The name Peleusball was formed from his two-part family name Pels Leusden, so it should be pronounced peleus (eu as in today ) and not pele-us . German patent No. 897930, first distributed by E. Leitz, owner Franz Bergmann, Berlin NW 6, Luisenstrasse 45.
Aspirette
An aspirette consists of two openings with a wider area in the middle. Aspirettes are mostly made of silicone, like the peleus balls.
application
First, the aspirette is put onto the pipette with the lower opening. In order to suck in the liquid, the air is first forced out by squeezing the aspirette and then the upper opening is closed with the finger. Now the liquid is sucked into the pipette and then the top of the pipette is closed with your finger. Finally, enough liquid is allowed to run out until the desired volume is in the pipette.
Howorka Ball
A Howorka ball consists of two composite rubber parts made of durable natural rubber, a suction ball and a stopper. The latter can be removed at any time if, for. B. liquid has accidentally entered the ball. The advantage of the Howorka ball over a Peleus ball is that it is easier to clean from the inside and can even be steam sterilized several times. In addition, a Howorka ball can be used with all pipette sizes thanks to the conical stopper; This is possible thanks to the conical shape of the stopper, while only pipettes with a certain minimum and maximum size can be used with a Peleus ball. The Howorka ball is also suitable for filling and blowing out burettes, filter tubes, capillaries and for loading, emptying and cleaning separation columns.
application
The Howorka ball is squeezed together with one hand and placed on the pipette opening. Now, by slowly opening the hand, the liquid is sucked up into the pipette by the resulting negative pressure. Now the Howorka ball is quickly removed and the index finger is pressed onto the opening instead (this requires a certain speed and practice). The fluid can now be dispensed by lifting the index finger in a controlled manner, thus adjusting the meniscus of the fluid. Repeated application and aspiration allow larger volumes than the two standard sizes of 20 ml and 50 ml to be aspirated.
Other equipment
In the laboratory, other constructions are also used to safely measure liquids.
Simple plastic pipetting aids are designed for pipettes of various volumes. The pipettes are plugged into the lower part of the device, and they are then filled with the liquid via the rack (or wheel). The exact volume is set or the pipettes are emptied by pressing the lever below.
Battery-operated pipetting aids for serological pipettes are ergonomically and safely designed. With some, the pipetting speed can be continuously adjusted with a knurled screw. Liquid is sucked in in a controlled manner by pressing the upper dosing button. The lower dosing button is used for precise dispensing of the liquid, which is also possible drop by drop with some devices. A sterile filter in the pipetting head prevents contamination.
Other laboratory aids for measuring liquids would be burettes and stand dispensers .
Individual evidence
- ↑ Peter A. Czeschinski: Protection against infection. Springer-Verlag, 2013, ISBN 978-3-322-83445-4 , p. 14 ( limited preview in Google book search).
- ↑ Max Gundel: Textbook of Microbiology and Immunobiology. Springer-Verlag, 2013, ISBN 978-3-662-25434-9 , p. 195 ( limited preview in Google book search).
- ^ Alfred Pingoud: Working methods of biochemistry. Walter de Gruyter, 1997, ISBN 978-3-11-016513-5 , p. 18 ( limited preview in the Google book search).
- ↑ Safety in the chemical university internship, An introduction for students, DGUV Information 213-026, PDF file .
- ↑ Friedrich Pels Leusden: Return-safe, safe pipetting . In: Münchner Medizinische Wochenschrift . Vol. 78, 1931, pp. 2156-2157.