What issues should we pay attention to when using pipetting filter tips?

Pipette filter tips are a commonly used laboratory tool that help experimenters precisely control the movement and distribution of liquids. However, there are some issues to be aware of when using pipette tips.

1. Check whether the pipette tip is clean before use. Failure to properly clean and disinfect pipette tips before use may introduce impurities or bacteria and affect experimental results. Therefore, it is recommended that proper cleaning and disinfection be carried out before use.

2. You need to choose the correct tip size. Different tip sizes are suitable for different capacity ranges. Improper selection may result in inaccurate aspiration or leakage. Therefore, when choosing to use a tip, the appropriate tip size should be selected based on experimental needs.

3. The depth of the suction head needs to be controlled. When operating, you should ensure that the depth of the suction head reaches just below the liquid level to avoid inhaling air or initiating foam. In addition, do not insert the tip too deeply, otherwise it may damage the pipette or damage the container.

4. Pay attention to the pipetting speed. When using pipettes to aspirate and dispense liquids, the speed of aspiration and discharge should be controlled. If the speed is too fast, bubbles or overflow may occur, affecting the experimental results.

5. The pipetting filter tip needs to be cleaned and maintained in time after use. The suction head should be cleaned immediately after use to remove residual matter or stains. At the same time, in order to maintain the working effect of the pipette, the tips need to be disinfected and replaced regularly.
a. Influence of electron effect: electron-withdrawing substituents increase the acidity, and electron-donating substituents reduce the acidity.

b. The presence of hydrogen bonds also affects the acidity of carboxylic acids:

The pKa1 of maleic acid is smaller than the trans isomer; the pKa2 of maleic acid is larger than the trans isomer.

Reason: The cis isomer ionizes a proton to generate a carboxylate negative ion, which can form a hydrogen bond with another carboxyl group to disperse the negative charge, but the second proton is difficult to ionize due to the formation of a hydrogen bond.

Regardless of whether there is an electron-withdrawing group or an electron-donating group in the ortho position of the carboxyl group of benzoic acid, the acidity is enhanced; generally, there are electron-withdrawing groups in the para- and meta-positions of the carboxyl group, which enhances the acidity, and weakens the acidity when connected with an electron-donating group.

c. Steric effect: The spatial structure that is conducive to H+ dissociation is highly acidic, while the spatial structure that is not conducive to H+ dissociation is weakly acidic.
By 向阳 翟


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