Micropipette is often used to absorb small or trace liquids in the laboratory. Pipettes of different specifications need different sizes of tips, and the shapes produced by different manufacturers are slightly different, but the working principle and operating method are basically the same. The pipette is a precise instrument, so be careful when using and storing it to prevent damage and avoid affecting its measuring range.
2. Pipette types
A. Air displacement micropipette The Air displacement micropipette is an adjustable pipette for measuring the volume between 0.1-1000 microliters. It requires disposable pipette tips touching the liquid. The following types of micropipettes correspond to four different colored tips:
1 – 10
2 – 20
This kind of pipette is driven by a piston to discharge air, whereby a vertically moving metal or ceramic piston creates a vacuum in a 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 can be very accurate and precise. However, it relies on the movement and compression of gas, so its accuracy will be affected by environmental conditions, especially temperature and user operation. Therefore, this instrument must be properly stored and calibrated, and the user must also be trained to practice correct and stable operation techniques.
Different types of micropipettes can be divided into: a. Volume adjustable or fixed b. Single cavity, multiple cavity or continuous cavity c. Conical tip or cylindrical tip d. Manual or electronic pipette
Regardless of manufacturers and price, every manufacturer recommends that users calibrate the micropipette every six months with frequent use. Pharmaceutical and food manufacturers require a calibration every three months. Schools that conduct chemical experiments can calibrate annually. Forensic and research departments that conduct numerous tests usually perform monthly calibrations.
B. Positive displacement pipette This type of pipette is similar to the air displacement micropipette, but it is less used and is usually used to avoid contamination, or for small, volatile or viscous substances, such as DNA. The main difference is that the disposable tip is a Microsyringe made of plastic and includes a piston that can directly discharge liquid.
C. Volumetric pipette The volumetric pipette allows the user to measure the volume of the solution with extremely high precision (four significant digits). This pipette has a larger ball connected to a narrow part at the top, which is engraved with a graduation line showing the volume (similar to a volumetric flask). Classic models include 10, 25, and 50 ml volumes. Volumetric pipettes are often used to prepare solutions from basic materials or to prepare titrants.
D. Graduated pipette A graduated pipette is a large pipette that contains a long tube with a series of graduated lines, similar to a graduated cylinder or burette, representing different volumes. It also needs to create vacuum. In the early chemical and biological experiments, the experimenter would breathe in with his mouth. Graduated pipettes usually have 5, 10, 25, and 50 ml specifications.
To prevent the inhalation of harmful substances, various manually or electronically controlled pipettes have been invented. Initially, pipettes were made of soda-lime glass. Many pipettes today are made of borosilicate glass. Disposable graduated pipettes are usually made of polystyrene. There are two common calibration methods for graduated pipettes:
a. Mohr pipette has a zero mark in front of the end. A certain volume of liquid is sucked into the pipette, usually to the maximum volume, and then partially removed as needed. b. Serological pipette does not have a zero mark. The required volume of liquid is sucked into the pipette and then removed.
Historically, the accuracy of graduated pipette is not as good as that of volumetric pipette, but with the advancement of production methods, the accuracy of today's graduated pipettes can be comparable to volumetric pipettes. The graduated pipette has a positive and negative error range, which is 0.6% to 0.4% of the theoretical pipette volume when measured at 20 °C. Graduated pipettes are manufactured according to ISO standards for accuracy and graduation arrangements. Type A has higher accuracy than type B.
E. Pasteur straw The Pasteur pipette is a plastic or glass pipettes used to transfer a small amount of liquid, but it is not marked with any volume scale or guideline. Pasteur's pipettes are often called pipette droppers or chemical droppers.
How to use a pipette?
When conducting research on analysis and testing, a pipette is generally used to measure small or trace amounts of liquid. Many people ignore the correct use of the pipette and its detailed operations. I will describe it in details in several aspects.
1. Range adjustment
When adjusting the range, if you want to adjust the volume from a large volume to a small volume, follow the normal adjustment method and turn the knob clockwise; but if you want to adjust the volume from a small volume to a large volume, you can first turn the scale knob counterclockwise to over the scale of the range. Then adjust it back to the set volume, so that the highest accuracy of measurement can be guaranteed.
During this process, do not turn the button out of the range, otherwise it will jam the internal mechanical device and damage the pipette gun.
2. Assembly of the tip
When putting the pipette tips on the pipette, many people will knock on the pipette tip box a few times. This is a wrong approach, because it will cause the internal parts (such as spring) of the pipette tips to be damaged. The instantaneous impact force generated by the knock makes parts loose, and even causes the scale adjustment knob to jam.
The correct method is to insert the pipette (apparatus) vertically into the tip of the pipette, and turn it slightly left and right to make it tightly combined. If it is a multi-channel (such as 8-channel or 12-channel) pipette, you can align the first pipe of the pipette with the first pipette tip, then insert it at an angle, and shake it forward and backward to lock it. The sign that the gun tip is clamped is slightly beyond the O-ring, and you can see that the connecting part forms a clear seal.
3. Methods of pipetting
Before pipetting, make sure that the pipette, pipette tips, and liquid are at the same temperature. When absorb the liquid, keep the pipette upright, and insert the pipette tip 2-3 mm below the liquid surface. Before absorbing the liquid, you can absorb and lose the liquid several times to wet the suction nozzle (especially when you want to absorb a liquid with a viscosity or a density different from water). At this time, two pipetting methods can be adopted.
A. Forward pipetting Press the button with your thumb to the first stop, then slowly release the button to return to the origin (aspirate a fixed volume of liquid). Then press the button to the first stop to discharge the liquid, pause for a while and continue to press the button to the second stop to blow out the remaining liquid. Finally, release the button.
B. Reverse pipetting This method is generally used to transfer high-viscosity liquids, biologically active liquids, easily foaming liquids or very small amounts of liquids. The principle is to absorb in more liquid than the set range first, without blowing out the remaining liquid when transferring the liquid. First press the button to the second stop, slowly release the button to the origin, and after sucking up, lean against the container wall to let the excess liquid back to the container along the wall. Then press the button to the first stop point to discharge the liquid of set range, continue to hold the button at the first stop point (don’t press it down), remove the tip of the residual liquid, and discard it.
4. Pipette placement
After use, you can hang it upright on the pipette holder, but be careful. When there is liquid in the pipette tip, do not place the pipette horizontally or upside down to prevent the liquid from flowing back and corroding the piston spring.
Common pipette brands
1. Top 10 Brands in China
A. Huaou B. Lichen Technology C. Rebs D. Lianhua Technology E. Zhiyunda F. Diaopu Optics G. Hongsheng H. Gida I. Precision Home J. Ruixin Office
2. Top 10 Foreign Brands
A. Eppendorf pipette (Germany) B. Gilson pipettes(America) C. Finnpipette (America) D. BIOHIT (Finland) E. BRAND (Germany) F. RAININ (America) G. NICHIRYO (Japan) H. SOCOREX (Switzerland) I. Hamilton (Switzerland) J. HTL (Poland)
Micropette is a classic laboratory tool. Each laboratory should be equipped with pipettes. Pipettes of various volume ranges, as well as manual and electronic pipettes, are the most commonly used instruments in daily laboratory work.