The accuracy and precision of pipetting not only requires matching of the tip and the pipette, but also a tip suitable for liquids. When a standard tip (PP) is used to remove a liquid having a small surface tension, it is easy to leave a film (such as a liquid containing a detergent) on the surface of the tip. Residues of the liquid can result in inaccuracies and inconsistencies in the pipetting results, as well as loss of some expensive samples. The reagents and samples used in many DNA and protein assays typically contain a detergent. The development of low adsorption tips is a common problem in order to improve liquid residue.

Different manufacturers use different techniques to make low-adsorption tips, so they are different in consistency, hydrophobicity, and chemical resistance. The following is a comparison of the chemical resistance of the low adsorption tips of various manufacturers.

material
Sartorius Optifit Standard Tip: 1000μ
Sartorius Optifit Low Adsorption Tip: 1000μl
Other manufacturers low adsorption tips: 1000μl
Sartorius Picus electric pipette: 50-1000μl, aspirate at 4 speeds, 1 speed discharge chemical reagent: isopropanol, acetonitrile, DMF (dimethylformamide), green food dye
Low adsorption pipette tips from 3 other manufacturers
96-well microplate spectrophotometer (Biotek)

Absorbance test
In the absorbance test, we used a staining reagent (green food dye dissolved in distilled water) to determine the residual liquid in the pipette tip after draining. Use the largest nominal volume of the measured tip to absorb the green reagent. The liquid is then drained directly back into the container. Next, rinse the tip 5 times with distilled water at the maximum capacity of the tip. The absorbance of the rinse was then measured using a spectrophotometer (405 nm) and the results were compared to a reference reagent. The absorbance of the rinse is directly related to the amount of liquid remaining in the tip.

Chemical resistance test
1000 μl Solvent: Repeat the pipetting of isopropanol, acetonitrile and dimethylformamide 20 times using a 1000 μl pipette tip. The tip was rinsed 3 times with distilled water. The effect of this treatment on the performance of the low adsorption tip was then analyzed using an absorbance test using a dyed liquid as a reagent. Repeat 6 tests for each of the 6 tips. The results of the chemically treated tips were compared to the results of the untreated standard and low adsorption tips.

Chemical resistance of low adsorption pipette tips <br> A variety of techniques have been used to create low adsorption surfaces for pipette tips. The most stable method produces a completely hydrophobic and non-leaching tip. As shown in Figure 1, there is a significant difference in chemical resistance between the low adsorption tips tested. The low adsorption function of some manufacturers' tips is significantly reduced after treatment with selected solvents. The performance of Sartorius low-adsorption tips after chemical testing was at the same level as without any chemical treatment, indicating that these tips were inert and leached. Autoclaving the Sartorius low-adsorption tips also did not affect the performance of the tips (data not shown).

Figure 1 Comparison of chemical resistance of low adsorption pipette tips