Working with bulb and volumetric pipettes
Pipettes are volumetric instruments for measuring volumes of liquid and are generally calibrated 'to deliver'. During the manufacturing process, they are individually volumetrically calibrated and provided with one or more calibration marks.
We distinguish between bulb pipettes and graduated pipettes (calibrated to deliver, TD, Ex), disposable micropipettes up to 200 μl (calibrated to contain, TC, In) and mechanic or electronic micropipettes, also called air-cushion pipettes.
Bulb pipettes
Bulb pipettes, also known as volumetric pipettes, are precise volumetric instruments used to measure and transfer a fixed volume of liquid. They usually have a bulb-shaped central section between two tubes, one of them with a tip. For smaller volumes, however, a straight tube design is used.
Volumetric pipettes are generally calibrated to “Ex” (TD = to deliver). This means that the specified volume of liquid is delivered, when used correctly when used correctly. Due to their small cross-section in the area of the ring mark, they generally provide greater measurement accuracy than graduated pipettes.
→ Types
Volumetric pipettes with one graduation mark, in which the liquid is allowed to drain completely according to the specified delivery procedure.
Volumetric pipettes with two graduation marks, in which only the volume defined between the two marks is delivered.
→ Calibration
Class AS: “Ex + 5 s”
Class B: “Ex”
Graduated pipettes
Graduated pipettes are graduated volumetric instruments used to measure and transfer different volumes of liquids. Unlike volumetric pipettes, they feature a volume scale in their cylindrical part that allows both the nominal volume and partial volumes to be measured and delivered.
Graduated pipettes are generally calibrated to“Ex” (TD = to deliver). This means that the scale indicates the respective volume of liquid delivered. Their graduation makes them flexible to use, although they generally offer lower measurement accuracy than volumetric pipettes.
→ Types of graduated pipettes:
Type 2 – Nominal volume at the top, complete delivery for both nominal and partial volumes.
Type 1 – Nominal volume at the bottom, partial delivery for all volumes.
Type 3 – Nominal volume at the bottom, complete delivery only for the nominal volume, partial delivery for all partial volumes.
→ Calibration:
Class AS: “Ex + 5 s”
Class B: “Ex”
How to work with bulb pipettes and graduated pipettes type 2
Filling
1. Fill the pipette with a pipetting aid to approx. 5 mm above the selected graduation mark.
2. Remove any liquid remaining on the outside of the tip of the pipette with a tissue.
3. Set the meniscus.
4. Wipe off any drop of liquid adhering to the tip.
Delivering
5. Hold the pipette vertically. Deliver the liquid with the tip of the pipette in contact with the inner surface of the inclined receiving vessel.
6. When the meniscus comes to a rest in the tip, the waiting time of 5 s begins (class AS only).
7. After the waiting time, draw the pipette tip upwards along the inner wall through a distance of about 10 mm to remove residual liquid.
Working with type 2 graduated pipettes is significantly quicker and simpler. With type 1 and type 3 pipettes there is a risk that with the always necessary second meniscus setting too much liquid is released, and that the sample needs to be prepared again (as also with bulb pipettes that have 2 marks).
How to work with graduated pipettes type 1 and type 3
When using type 1 or type 3 graduated pipettes (zero point at top), the meniscus must
1. first be set at the zero point and then the liquid be run out to slightly above the desired partial volume.
2. After a waiting time of 5 s, the meniscus should be set a second time.
FAQ
You can choose between different pipette controllers/aids vom BRAND:
- macro pipette controller (easy manual handling)
- accu-jet S (motorized controller)
- classic pipette fillers (also named Peleus Ball)
