Common problems and precautions in basic operation of knowledge sharing of pipette

Quite a lot of people think that the pipette is a very simple instrument, and its operation is also very simple There is no need to talk about it, not to mention any training courses In fact? A good habit of using the pipette is very helpful for prolonging the service life of the pipette, improving the precision of the pipette and maintaining the health of the user Here are some common bad operation behaviors in the laboratory Let's see if you have the same habitual mistakes? First, install the suction head In the laboratory where the pipette is frequently used, the sound of knocking on the suction head can be heard one after another, which adds a bit of music to the boring laboratory life In a closer look, it turned out that the user was afraid that the suction head could not be tightened After the suction head was installed on the pipette, he knocked several times in the suction head box, hoping to ensure the sealing of the pipette through this impact force What's wrong with this operation? First, under the impact, the suction head may deform and affect the precision of liquid transfer; second, the part of the handle of the pipette that contacts the suction head will gradually become rough and difficult to ensure the sealing after several times of strong friction, and in order to achieve good sealing, more impact force is required, so the vicious cycle begins; Third, the handle of the small range pipette is relatively thin, which is likely to become a fishing hook under the constant impact; fourth, sometimes the impact force is greater than the force of the pipette falling to the ground, and some of the precision parts in the pipette are likely to strike at any time Second, suction angle In order to observe the condition of the sample in the suction head easily, many users will let the pipette keep a 45 ° angle or even more close to the horizontal angle during the suction process But it's wrong again First, when the sample is close to or reaches the maximum volume of the suction head, the large angle inclination of the pipette makes it easy for the liquid to slip into the sleeve handle of the pipette, thus polluting or even corroding the piston of the pipette, and at the same time, it is easy to cause cross contamination of the sample; Second, the large angle inclination of the pipette will also increase the contact surface between the outer wall of the suction head and the liquid, so that when the suction head leaves the liquid surface, there will be more liquid left on the outer wall, and it is easy to leave the suction head together with the liquid in the suction head when draining, so as to reduce the precision of the pipette, and these residual liquid for small range (such as 2ul and 10ul ）As far as the pipette is concerned, its damage to accuracy is likely to be fatal! Third, suction speed Have you ever had liquid back suction into the piston during operation? It is often seen in the laboratory that in order to "improve efficiency", the user's thumb is released rapidly when sucking, which makes the liquid rush into the suction head quickly As we all know, this forces the liquid to form a turbulent state after entering the suction head Thus, for the small and medium range pipettes, there will be invisible vapor mist entering the inside of the pipette, and for the large range pipettes, there will be liquid rushing directly into the inside of the pipette The final result is to pollute or even corrode the piston of the pipette, which is easy to cause cross contamination of the sample and also has an impact on the accuracy Fourth, storage Do you place the pipette flat on the table after using it? A considerable number of users will directly place the pipette on the experimental platform after the use of the pipette, and those who are interested in neatness may put the pipette in the drawer In fact, this is not good! In the process of liquid transfer operation, it is inevitable that liquid will enter into the internal part of the pipette In the flat state, the liquid will stay on the piston and other parts, polluting the piston and even corroding the piston after accumulating over time In the problems listed above, the corrosion of piston is often mentioned Someone might say: the piston of my pipette is corrosion-resistant! But I still have to remind two points: first, except for a few low-end pipettes that use all plastic accessories, most of the piston components of the pipette have metal parts; second, as long as the piston is polluted, no matter what the piston material is, there may be problems such as the decrease of the internal air tightness of the pipette and the cross contamination of the samples In a word, it is necessary for each laboratory to establish and perfect SOP (standard operating procedures) for the use of the pipette, and strictly manage the operation of the pipette There are six steps in a complete liquid transfer cycle: 1 Installation of suction head 2 Capacity setting 3 Pre washing suction head 4 Suction 5 Discharge 6 Removal of suction head Each step has operation specifications to be followed Here is a detailed introduction of the key precautions of the pipette 1 After the suction head enters the suction head at the lowest end of the sleeve handle of the pipette, if the operation is carried out in the suction head box, shake the pipette or slightly rotate the pipette (only the single pipette can rotate) for 1-2 seconds while gently pressing it down; if the suction head is used in bulk, slightly rotate the suction head 1-2 while gently pressing the suction head towards the direction of the pipette by hand Seconds If this operation does not achieve the desired tightness, it is necessary to check the suction head and the pipette 2 Coarse adjustment of capacity setting: quickly adjust the volume value to close to the expected value by turning the button; fine adjustment: when the volume value is close to the expected value, place the pipette horizontally in front of your eyes, and slowly adjust the capacity value to the expected value by adjusting the wheel, so as to avoid the influence caused by visual error When it is adjusted from large volume to small volume, it is just enough; when it is adjusted from small volume to large volume, it needs to be adjusted over one third of a turn and then returned, because there is a certain gap in the counter, which needs to be made up 3 After we install a new gun head or increase the capacity value, the liquid to be transferred should be sucked and discharged twice or three times, so as to form a homogenous liquid film on the inner wall of the gun head, ensure the precision and accuracy of the liquid transfer work, and make the whole liquid transfer process highly reproducible Secondly, when the organic solvent or highly volatile liquid is absorbed, the volatile gas will form a negative pressure in the white sleeve room, resulting in liquid leakage At this time, we need to pre wash four to six times to make the gas in the white sleeve room saturated, and the negative pressure will disappear automatically The viscous liquid can be accurately transferred by the way of pre wetting the gun head First, suck in the sample liquid, and then blow it out The inner wall of the gun head will absorb a layer of liquid, so that the surface absorption reaches saturation, and then suck in the sample liquid, and finally the volume of the liquid will be very accurate 4 Suction depth and angle (1) immersion depth of suction head: P2, P10 ≤ 1mm; P20, P100, P200 ≤ 2mm; P1000 ≤ 3mm; p5ml, p10ml ≤ 4mm; of course, the specific immersion depth should be flexibly controlled according to the size of the container containing the liquid Note: 1) if it is immersed too deep, the hydraulic pressure will have a certain impact on the accuracy of suction; 2) make the outer wall of suction head contact with the liquid as little as possible; 3) suction angle: keep the pipette in a vertical state during the process of liquid transfer, with the maximum inclination not more than 20 °; 4) Suction speed: in the process of suction, the downward pressure of the thumb must be slowly reduced to make the liquid rise evenly and slowly in the suction head; 5) retention time: for a large range of liquid (ml level) and a liquid whose viscosity is significantly higher than that of the water sample, the suction head must stay in the liquid 3-5 after loosening the thumb during suction It can only be removed after seconds (because the movement of the liquid into the suction head is relatively time-consuming, it must be ensured that the liquid reaches the dynamic balance) 5 When discharging liquid, the gun head shall be close to the vessel wall First press the discharge button to the first stop point, and then press it to the second stop point after a slight pause, so as to ensure that there is no residual liquid in the gun head If there is residual liquid after this operation, the gun head should be replaced Forward suction: during operation, the suction button can be pressed to the first gear to suction and release When draining, first press the first gear to pump out most of the liquid, then press the second gear to drain the remaining liquid Reverse suction: when suction, press the button directly to the second gear, and then release it, so that some more liquid will be inhaled, and when the liquid is ejected, just press the first gear The multi suction liquid can compensate the surface adsorption inside the gun head The reverse suction is generally used in combination with the pre wetting suction method, which is suitable for viscous liquid and volatile liquid (3-5 seconds residence time is required for both suction and discharge) It is also suitable for small volume pipettes 6 The removed suction head and the discharged suction head must not be mixed with the new suction head to avoid cross contamination After the completion of the use of the pipette, the pipette must be adjusted to the maximum range, and then hung (it can be hung on the special support, or on the metal crossbar of the test bench cabinet) When there is liquid in the gun head, do not level or invert the pipette, so as to avoid liquid backflow corroding the piston spring Other precautions: 1 Lift the liquid transfer gun off the liquid level, stop for about one second, and observe whether there is any liquid drop flowing out slowly If there is any flowing out, it indicates that there is air leakage The reason may be that the gun head is not tightened, or the internal air tightness of the liquid transfer gun is not good 2 Slow suction and slow release, control the expansion and contraction speed of the spring, too fast suction speed will produce recoil and blister, resulting in inaccurate volume of liquid transfer; the remaining liquid on the outer wall is dipped with filter paper to wipe the attached liquid drop 3 The temperature of the hand will affect the accuracy of the pipette Although the shell of the holding part of the pipette is generally made of low thermal conductivity material, the temperature of the hand will still be transmitted to the pipette when the holding time is long The components in the pipette may be deformed due to the temperature change, thus affecting the accuracy of the pipette Therefore, attention should be paid in the operation process: first, in the operation process, as long as the thumb force is not required, try to hang the pipette on the hand by the finger hook and release the palm; second, generally, the continuous pipette should not exceed half an hour, if the workload is heavy, the hand can be changed for operation In this way, while minimizing the influence of hand temperature, your precious hand can also get a certain rest 4 The precision values of the high density / low density sample pipette are all based on the transferred pure water If the density of the sample is very different from that of the water, the precision will be correspondingly poor Therefore, it is necessary to find out the density of the sample before the transfer, and then adjust the range to the product of the volume to be transferred and the density For example, if the density of a sample is 1.2g/cm3 and you need to transfer 300ul, you should set the range to 360ul This is only a rough method of adjustment Strictly speaking, it also requires the accurate calculation of the meter or balance as an auxiliary tool In a word, it's basically a job requiring experience 5 Pay attention to three points for high temperature / low temperature samples: first, never wet and wash the suction head before transferring; second, change the suction head every time; third, the suction and discharge should be completed as soon as possible (quoted above: "silly bird: not professional professional pipette blog") this is the book