What are the precautions for using the pipette? See if you do it all?

1. 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 be adjusted to exceed the set volume scale first, and then back to the set volume, so as to ensure the accuracy of the pipette

2. Assembling the pipette tips

Insert the pipette vertically into the tip, rotate it half a turn left and right, and tighten it. The method of hitting the tip with a pipette is very inadvisable. Long-term operation in this way will cause the parts of the pipette to loosen due to the impact, which will seriously cause the knob to adjust the scale to get stuck.

3. For suction and discharge, the tip of the vertical suction tip is immersed below 3mm of the liquid surface. Before suction, the tip should be pre-rinsed in the liquid. Slow suction and slow discharge. If the amount is small, the tip of the tip should be reliable on the inner wall of the container.

4. The pipette that sucks liquid should not be laid flat. The liquid in the pipette tip can easily contaminate the inside of the gun and may cause the spring of the gun to rust.

5. The pipette should be adjusted to the maximum scale after each experiment to allow the spring to return to its original shape to extend the life of the pipette

6. When sucking the liquid, the thumb must be released slowly and steadily, and it is not allowed to release suddenly, in order to prevent the solution from being sucked too fast and rushing into the liquid dispenser to corrode the plunger and cause air leakage.

7. In order to obtain higher accuracy, the tip needs to absorb the sample solution once in advance, and then formally pipette, because when sucking serum protein solution or organic solvent, a layer of "liquid film" will remain on the inner wall of the tip, resulting in the discharge volume. Errors are caused by being too small.

8. Liquids with high concentration and viscosity will cause errors. In order to eliminate the compensation amount of the error, the amount of compensation can be determined by experiment. The amount of compensation can be set by changing the reading of the reading window with the adjustment knob.

9. The liquid dispenser can be calibrated by weighing and calculating the weight of the pure water taken with an analytical balance. 1mL of distilled water weighs 0.9982g at 20°C. The set range is within the range of the pipette. Do not turn the button out of the range. , otherwise it will jam the mechanism and damage the pipette.

10 When setting the range, please pay attention: the number is clearly displayed in the display window, rotate to the desired range

11. The pipette is strictly prohibited to absorb highly volatile and corrosive liquids (such as concentrated acid, concentrated alkali, organic matter, etc.).

12. It is strictly forbidden to use a pipette to mix the liquid.

13. Do not use a large-scale pipette to remove small volumes of liquid, so as not to affect the accuracy. At the same time, if you need to pipette a larger amount of liquid outside the range, please use a pipette for operation.

In general, there are some basic operating principles that must be followed in order to prevent errors in the volume picked up. There are three main factors that affect the suction volume error: ①hydrostatic pressure; ②tip wetting; ③hydrodynamics. When the sample volume is reduced from the milliliter range to the microliter range, the relationship of physical forces changes, which, for sample loading, means that the force effects of the liquid surface are in contrast to the force effects of its volume or mass (e.g., gravity) ratio has increased, so pipette manufacturers must carefully consider this situation in the design and construction of pipettes and tips, and must also take care when using them.

Hydrostatic pressure: When aspirating liquid, the pipette tip can only be immersed in a few milliliters of the liquid to ensure the same hydrostatic pressure conditions as when expelling the liquid, therefore, the pipette must be dispensed in an almost vertical manner because of the tilt method will reduce the height of the liquid column, resulting in too much liquid being drawn. If the pipette is drawn vertically at 30°C, up to 0.15% more liquid can be drawn.

Tip Wetting: When the tip is emptied, there will still be some residual liquid left on the side of the tip in the form of a thin film 6f, the amount of which depends on the interaction of the liquid and the tip surface, so it is a constant, But it varies according to the liquid material. For aqueous solutions, this wetting effect should be considered when constructing the pipette. For liquids with high viscosity such as protein solutions, it is recommended to pipette the liquid several times before adding samples to ensure the consistency of sample addition.

Hydrodynamics: The third effect on volumetric aspiration is the release of liquid from the outer wall of the pipette tip, in which tip geometry plays a key role. To ensure stable conditions during sample addition, the tip of the sampler should rest on the tube wall, so that the liquid can flow out along the tube wall without droplets, the formation of which can be prevented due to its surface tension. Liquid is released from the tip. If the tips are installed incorrectly or use mismatched tips, the relative sample addition error will reach more than 0.4%.