Accurate analytical methods are especially important for biochemical experiments. The first to be mastered in various biochemical analytical techniques is accurate pipetting techniques. To do this, we need to use various types of pipettes , some of which are not used in chemical experiments and are commonly used in biochemical experiments. Here it is les
Let's talk about these various pipettes .
1 Dropper dropper is easy to use and can be used for semi-quantitative pipetting. The pipetting amount is 1mL~5mL. The commonly used pipetting range is 2mL, and the dripper of different sizes can be replaced. There are two types of dropper, long and short. A new type of dropper with a scale and a buffer bulb can pipette more accurately than a normal dropper and prevent liquid from sucking into the dripper.
2 pipette (sipper)
The pipette (sipper) should be cleaned until the inner wall is not hanged before use. The straw of 1mL or more can be brushed with a special suction brush. The 0.1mL, 0.2mL and 0.5mL straws can be soaked with detergent. If necessary, ultrasonic cleaner can be used. Cleaning. Since chromic acid lotion is carcinogenic, try to avoid it. If a large number of batches of pipettes need to be washed after washing, use a flushing bucket, place the tip of the pipette up in the bucket, rinse it with tap water multiple times, and rinse with distilled or non-ionized water.
There are two types of straws, one is not indexed, called the big belly straw, the accuracy is higher, the relative error is 0.7%~0.8%, the grade B is 1.5%~0.16%, the liquid self-calibration line Flow to the mouth (with residual liquid), wait for 15 s for Class A and 3 s for Class B. The other type of straw has an indexing straw, and the tube body is a uniform and thin glass tube. The upper part is uniformly engraved with a dividing line indicating the volume, and the accuracy is lower than that of the big belly straw. The relative error A is 0.8% to 0.2. %, B grade is 1.6%~0.4%, grade A and grade B have A and B on the straw, "fast" is fast flow, and "blow" is blown, no "blow" The word straw cannot blow out the residual liquid from the tip. Wipe the tip of the tube with absorbent paper before absorbing or discharging the solution.
3 Micro-injector micro-sampler is often used as an injector for gas and liquid chromatographs, and is mainly used as a sampler for electrophoresis experiments in biochemical experiments.
Generally, it can be divided into two types: no liquid storage and no liquid storage.
(1) A very small amount of liquid injection below 10 μL.
No liquid micro-injector: The stainless steel core of the injector passes directly to the tip of the needle without depositing liquid.
(2) 10μL～100μL There is a liquid micro-injector: the tip of the stainless steel is empty, the plunger of the injector can't reach, so there will be air or liquid in the tube. The precautions for use are: 1 Concentrated alkali solution to avoid corrosion of glass and stainless steel parts; 2Because there is liquid, it is necessary to pull back and forth several times to absorb all the bubbles in the needle tip tube; 3 needle tip tube inner hole is very small, especially after use Immediately after the protein solution, the needle tip tube must be cleaned to prevent clogging. If the needle tip tube is blocked, it can't be fired. Only the stainless steel wire of φ0.1mm can be used for patient collusion. 4 When the sampler is not wet, the core can not be pulled back and forth to avoid wear and leakage; 5If the sampler is inside Blackening means that there is stainless steel oxide. You can use a small amount of soapy water with a core and pull it back and forth several times to remove it.
4 automatic pipette
This type of automatic pipette is used extensively in biochemical experiments (such as Eppendorf, Biohit, and IKA pipettes). It is mainly used for rapid quantitative pipetting of multiple repetitions. It can be operated with only one hand, which is very convenient. The accuracy of pipetting (ie, capacity error) is ± (0.5% to 1.5%), and the precision of pipetting (ie, repeatability error) is smaller, ≤0.5%.
Pipettes can be divided into two types: one is a fixed capacity, and the more commonly used ones are 100 μL. Each type of pipette has its own special polypropylene plastic tip. The tip is usually used once. It can also be re-used after ultrasonic cleaning. The tip can also be autoclaved at 120 °C. It is a pipette with adjustable capacity. It is commonly used in several sizes such as 200μL, 500μL and 1000μL.
Adjustable pipettes (Eppendorf, Biohit, and IKA pipettes) are operated by turning the knob on the upper part of the pipette with your thumb and forefinger to bring the number of the desired volume to the digital window. Insert a lower end of the pipette. Plastic tip, and tighten to ensure airtightness, then hold the upper part of the liquid extractor with four fingers together, press the button on the top of the plunger rod with your thumb, press down to the first stop point, and pipette the tip of the pipette Insert the solution to be taken, slowly release the button, suck the liquid, and stay for 1 to 2 seconds (the sticky solution can be extended for a long time), slide the tip along the wall out of the container, wipe it off with absorbent paper. The liquid on the surface of the tip may be attached. When the liquid is drained, the tip touches the inclined wall. Press the button to the first stop point for one second (the liquid with a thick viscosity should be extended for a long time), and then press the second stop. Point, blow out the remaining solution at the tip of the tip. If it is not convenient to remove the tip by hand, press the tip of the tip to push the tip into the waste bin.
The precautions for using automatic pipettes (Eppendorf, Biohit, and IKA pipettes) are:
1 When sucking the liquid, be sure to slowly and smoothly release the thumb. Never let it suddenly loosen, in case the solution is sucked too fast and flush into the pipette to corrode the plunger and cause air leakage.
2 In order to obtain higher precision, the sample solution needs to be sucked once before the sample is taken, and then the liquid is officially pipetted. Because the serum protein solution or the organic solvent is taken up, a “liquid film†remains on the inner wall of the tip, causing partial discharge. Small and error.
3 Liquid with high concentration and viscosity will produce an error. The amount of compensation to eliminate the error can be determined by experiment. The compensation amount can be set by changing the reading of the reading window with the adjustment knob.
4 The weight of the pure water taken by the analytical balance can be weighed and calculated to correct the pipette. The weight of 1 mL distilled water is 0.9982 g at 20 °C.
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