Summary of pipette basics
Pipettes achieve different accuracy and precision through a variety of designs, including simple pipettes made of a piece of glass, to complex adjustable or electronically controlled pipettes. The accuracy of the measurement varies greatly depending on the type. . Today, Sister Xiaoxi will have a good chat with everyone about pipettes.
Pipettes, also known as "quantitative pipettes", "pipettes", and "pipettes" are experimental instruments designed to measure the volume of liquids and transfer them to other containers. Often used in biological experiments or chemical experiments.
Classification and principle of pipettes
Common pipettes can be divided into the following five types: exhaust micropipette, positive displacement pipette, positive displacement pipette, graduated pipette, and Pasteur pipette.
1. Exhaust type micro pipette
Exhaust type micropipette, often called "exhaust type pipette", referred to as "pipette gun", is an adjustable pipette used to measure the volume of 0.1-1000 microliters. This type of pipette requires a disposable tip, which is in contact with the liquid. The exhaust type micropipette is driven by a piston to discharge air, whereby the vertically moving metal or ceramic piston creates a vacuum in the closed tube. When the piston pumps upwards, the second half of the gas is compressed, and the first half of the space becomes a vacuum. At this time, the liquid near the tip of the gun enters the vacuum part, and then can be transferred or discharged again. This pipette has high accuracy and precision and is suitable for routine pipetting operations. However, because it relies on the movement and compression of gas, the accuracy is greatly affected by environmental conditions, especially temperature, air pressure, and user technology. Therefore, this instrument must be properly stored and calibrated, and the user must also be trained to practice correct and stable operation techniques.
Common brands of exhaust micropipettes include Eppendorf, Gilson, ErgoOne, etc.
2. Positive displacement pipette
This type of pipette is similar to the vented pipette, but is less used, usually used to avoid pollution, or used for small, volatile or viscous substances, such as volatile organic compounds, DNA, etc. The main difference is that the disposable tip is a Microsyringe with a piston, the piston is made of plastic, and the piston is in direct contact with the liquid to suck and discharge the liquid.
3. Volumetric pipette
Volumetric pipettes are also called "pipettes" and have extremely high precision (four significant figures). This type of pipette has a ball, and there is a graduation line above the ball to identify only the pipette The fixed volume. Typical models have volumes of 10, 25, and 50 milliliters. Volumetric pipettes are often used to prepare solutions from basic materials or to prepare titrants.
4. Serological pipette
Serological pipettes, also known as graduated pipettes, graduated pipettes, etc., are long glass tubes with a series of graduated lines that can draw liquids of different volumes. Such serological pipettes usually have 5, 10, 25, and 50 ml specifications. Serological pipettes have a positive and negative error range, which is 0.6% to 0.4% of the theoretical volume when measured at 20°C. Serological pipettes are manufactured according to ISO accuracy and scale arrangement standards. Type A has higher accuracy than type B.
Precautions:
1. The pipette (pipette) should not be dried in the oven.
2. The pipette (pipette) cannot pipette solutions that are too hot or too cold.
3. The same pipette should be used as much as possible in the same experiment.
4. After the pipette is used, it should be rinsed with tap water and distilled water immediately and placed on the pipette rack.
5. Pipettes and volumetric flasks are often used together, so the relative volume of the two is often calibrated before use.
6. When using the pipette, in order to reduce the measurement error, the starting point should be the top scale (0 scale) every time, and the required volume of the solution should be discharged down instead of sucking as much volume as needed.
7. There are old style and new style pipettes. The old style tube body is marked with the word "Blow". You need to use an ear wash ball to blow out the residual liquid at the nozzle. There is no new type, do not blow out the residue of the nozzle, otherwise it will cause too much liquid to be taken.
5. Pasteur pipette
The Pasteur pipette is a plastic or glass pipette used to transfer a small amount of liquid, but it is not marked with any volume scale or guideline. Pasteur pipettes are more commonly called droppers and chemical droppers.
The structure of the pipette
At present, the commonly used exhaust micropipette and positive displacement pipette in laboratories have the following structures: components for sucking and discharging liquid, volume adjustment dial, disposable pipette tip, pipette ejector button, and pipette ejector rod.
The difference between vented and positive displacement pipettes
The accuracy of the exhaust type micropipette is greatly affected by environmental conditions, and the correct pipetting operation can minimize the impact of the environment.
The correct aspiration operation of commonly used exhaust micropipettes:
A. Hold the flat part of the micropipette in the palm in a vertical direction, and press the operation button to the first stop position
B. Just immerse the tip below the liquid surface, release the button steadily, and then wait for a while until the liquid enters the tip, and make sure that there are no bubbles in the tip
C. Gently press the operating button to the first stop point, and after about 1 second, continue to press the operating button down to the second stop point of this operation. The function of this operation is to drain the solution in the mouth
D. Release the button to return to the starting position
as the picture shows
The positive displacement pipette sucks the volume of the actual scale and a certain amount of excess liquid, and its operation method is slightly different from that of the exhaust type:
A. Hold the flat part of the micropipette vertically in your palm, and place the button in the second stop position
B. Just submerge the tip below the liquid surface. Release the button steadily, the liquid enters the tip, and make sure that there are no bubbles in the tip
C. Put the button at the first stop position to discharge the liquid, and keep the operation button at the first stop position, so that a small amount of liquid that does not include the pipetting volume range remains in the nozzle
D. Press the button to the second stop position to discard excess liquid
as the picture shows
1. Use the right tip
In order to ensure better accuracy and precision, it is recommended that the pipetting volume be within the range of 35%-100% of the tip.
2. Set the pipetting volume
Adjusting from a large range to a small range is the normal adjustment method, just rotate the scale counterclockwise
When adjusting from a small range to a large range, it should first be adjusted to exceed the set volume scale, and then back to the set volume, so as to ensure the accuracy of the pipette
3. Installation of the suction head
For most brands of pipettes, especially multi-channel pipettes, it is not easy to install the pipette tip: in order to achieve a good seal, insert the pipette vertically into the pipette tip, rotate it half a circle left and right, and tighten it. There are also people who use the pipette to repeatedly hit the tip to tighten, but this operation will cause the tip to deform and affect the accuracy. In severe cases, the pipette will be damaged, so such operations should be avoided. Some multi-channel pipettes are equipped with O-rings, matched with a tip with a front stop point, and an ideal seal can be achieved with a light pressure.
4. The immersion angle and depth of the tip
The immersion angle of the suction head is controlled within 20 degrees of inclination, and it is better to keep it upright.
