Accurate analysis methods are extremely important for biochemical experiments. Among various biochemical analysis techniques, the first thing to be mastered is accurate pipetting technology. To this end, various forms of pipettes are used, some of which are unused by students in chemical experiments but commonly used in biochemical experiments. The figure below lists some commonly used pipetting instruments in biochemical experiments.
â‘´ Dropper
It is easy to use and can be used for semi-quantitative pipetting. The pipetting volume is 1mL-5mL, commonly used 2mL, can be changed to different sizes of drippers (Figure 1 (A)). There are two types of dropper, long and short. A new dropper with scale and buffer bubble is newly added, which can transfer liquid more accurately than ordinary dropper and prevent liquid from being sucked into the dripper.
⑵ Pipette (pipette)
The straws should be washed until the inner wall does not hang water drops before use. The straws above 1mL should be washed with a special brush for straws. The 0.1mL, 0.2mL and 0.5mL straws can be soaked with detergent, and can be cleaned with an ultrasonic cleaner if necessary. Due to the carcinogenic properties of chromic acid lotion, it should be avoided as much as possible. If a large number of straws are washed after washing, you can use a washing bucket, put the tip of the straw up into the bucket, rinse it with tap water for many times, and then rinse it with distilled or deionized water.
There are two kinds of straws, one is non-indexed, called fat belly straw (figure 1 (F)), the accuracy is high, its relative error is A level 0.7% ~ 0.8%, B level 1.5% ~ 0.16%, the liquid flows from the marking line to the mouth (with residual liquid left), Class A waits 15s, and Class B waits 3s.
The other type of straw is an indexing straw. The body of the tube is a glass tube of uniform thickness. The index line indicating the volume is evenly engraved on it. Its accuracy is lower than that of a fat belly straw. The relative error is A level 0.8% ~ 0.2%. Grade B is 1.6% -0.4%, grade A and grade B have A and B on the straw body, the word "fast" means fast flow type, the word "blow" means blow-out type, no "blow" word Do not blow out the residual liquid from the tip of the pipette. Wipe the tip of the tube with absorbent paper before aspirating or placing the solution.
⑶ Micro sampler
The micro sampler is often used as a sampler for gas and liquid chromatographs. It is mainly used as a sampler for electrophoresis experiments in biochemical experiments. It can usually be divided into two types: no storage solution and stored solution.
1) 0.5mL ~ 5mL non-retained micro sampler: The stainless steel core of the sampler directly leads to the tip of the needle, and no liquid will appear, so it can be used for the injection of very small amounts of liquids under 5mL.
2) 10mL ～ 100mL with liquid storage micro sampler: the stainless steel needle tube part is an empty tube, and the plunger of the sampler cannot reach, so there will be air or liquid in the tube. The precautions for its use are: ①Alkaline solution to avoid corrosion of glass and stainless steel parts. ② Because there is liquid stored in it, it is necessary to pull back and forth several times to aspirate the liquid, and exhaust all the air bubbles in the needle tip tube. ③ The inner hole of the needle tip tube is extremely small. After use, especially after absorbing the protein solution, the needle tip tube must be cleaned immediately to prevent blockage. If the needle tip tube is blocked, it cannot be burned, and only φ0.1mm stainless steel wire can be used to patiently collude. ④ Do not pull the core back and forth when the sampler is not wet to avoid abrasion and air leakage. ⑤ If the sampler is black and has stainless steel oxide, you can dip the core in a small amount of soapy water and pull it back and forth a few times to remove it.
â‘· Automatic liquid picker
Such pipettes are widely used in biochemical experiments. They are mainly used for rapid and quantitative pipetting with multiple repetitions, and can be operated with only one hand, which is very convenient. The accuracy of pipetting (ie, volume error) is ± (0.5% to 1.5%), and the accuracy of pipetting (ie, repeatability error) is smaller, ≤0.5%.
Pipettes can be divided into two types: one is fixed volume, commonly used are 100ml, 200mL and 1000mL, etc .; the other is adjustable capacity pipette, commonly used are 200mL, 1000mL and 5000mL, etc. Specs. Each pipette has its own special polypropylene plastic tip. The tip is usually used once, of course, it can also be reused after ultrasonic cleaning, and this type of tip can also be autoclaved at 120 ℃.
The operation method of the adjustable automatic pipette is to use the thumb and index finger to rotate the knob on the upper part of the pipette, so that the number window shows the number of the required volume, insert a plastic pipette tip at the lower end of the pipette, and tighten to ensure Airtight, then hold the top of the pipette with four fingers together, press the button on the top of the plunger rod with your thumb, press down to the first stop point, insert the pipette tip into the solution to be taken, slowly loosen Open the button, suck up the liquid, and stay for 1 to 2 seconds (longer residence time for a viscous solution), slide the tip out of the container along the wall, wipe off any liquid that may adhere to the surface of the tip with absorbent paper, and drain When the tip touches the inclined wall, first press the button to the first stop point, and stay for one second (the viscous liquid needs to be longer), then press to the second stop point, and blow out the remaining solution at the tip of the tip If it is not convenient to remove the suction head by hand, you can press the de-sucking push rod to push the suction head into the waste tank.
The precautions for the use of the automatic pipette are: ①Always release your thumb slowly and steadily when drawing liquid, and never allow it to be released suddenly, to prevent the solution from being drawn too fast and rushing into the pipette to corrode the plunger and cause leakage gas. ② In order to obtain higher precision, the pipette tip needs to suck up the sample solution once, and then formally pipette, because when the serum protein solution or organic solvent is sucked, a layer of "liquid film" will remain on the inner wall of the pipette tip, causing a discharge Too small to produce errors. ③Liquids with high concentration and viscosity will produce errors. To eliminate the error compensation amount, it can be determined by experiment. The compensation amount can be set by adjusting the knob to change the reading of the reading window. ④The analytical device can be used to weigh the weight of pure water and calculate it to correct the liquid picker. 1mL of distilled water weighs 0.9982g at 20 ℃.
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