For laboratory scientists, this inherent resistance presents a unique set of challenges. The properties of these liquids—cohesion and adhesion—can lead to inaccurate measurements, inconsistent experimental results, and even physical strain during manual pipetting. Therefore, mastering the complexities of handling viscous liquids is not only about precision, but also about ensuring the reliability and reproducibility of scientific research.
Viscous liquids commonly found in laboratory workflows
Saccharified liquid
Glycated liquids are composed of sugar and have a stronger adhesion to the pipette tip wall and a relatively higher cohesion than other viscous liquids. The viscosity of these liquids varies with the degree of dilution. Since these liquids can stick to the tips, slowing down the tip withdrawal speed after aspirating and dispensing can help avoid the formation of bubbles and droplets and ensure clean aspiration and dispensing.
Volatile viscous liquid
Volatile viscous liquids are mixtures of glycerin/PEG and volatile solvents such as ethanol or isopropyl alcohol. Added glycerol/PEG increases viscosity, while volatile solvents increase vapor pressure. Therefore, when pipetting, the user can use the default aspiration flow rate for water. However, the dispensing flow rate needs to be reduced. In order to solve the dripping problem caused by increased vapor pressure, it is necessary to add a section of air column after aspiration to ensure the accuracy of pipetting.
Thick surfactant liquid
Viscous surfactant liquid is a mixture of surfactants and viscous glycated liquid. The most commonly used viscous surfactants are Tween® 20 and Triton® X - 100, with viscosities up to 400 millipascal seconds (mPa). These liquids have higher adhesion to pipette tips but lower cohesion. Viscous surfactants require a slower aspiration flow rate with minimal evacuation of the liquid. The dispensing flow rate needs to be reduced to ensure that the liquid has enough time to slide off the pipette tip.
Oil
Oils with similar properties to viscous surfactants can be treated using the above process. The oil takes longer to completely slide off the tube wall, which means the pipette takes longer to dispense cleanly. Slower tip withdrawal helps reduce the loss of oil that adheres to the outer wall of the pipette tip, but requires longer clean dispensing of the oil because the oil's adhesion to the tip is higher than the oil's cohesion. liquid settling time, causing delays.
Best way to dispense viscous liquids
reverse pipetting
Reverse pipetting is one of the most common techniques for handling viscous liquids. In this method, more liquid is drawn into the pipette than is needed. Then dispense the required volume, leaving excess liquid. This technique is particularly useful for reducing bubble formation and ensuring accurate volume. Reverse pipetting improves accuracy, especially with very viscous solutions, by ensuring that the pipette tip is completely wetted and then dispensing only the required volume.
two-step draining
The two-step drain method is designed to improve accuracy when handling viscous liquids. First, dispense a portion of the liquid slowly to ensure that the required volume is transferred precisely. Then, quickly drain off the remaining liquid. This two-stage approach ensures fluid is released in a controlled manner, minimizing the chance of air entrainment and ensuring consistent, precise dispensing.
Contact Drainage Strategy
A contact dispensing strategy involves direct contact of the pipette tip with the wall or surface of the receiving container. By touching the tip to the side of the container, the viscous liquid can flow down the container wall, reducing the chance of sticking to the tip or forming droplets. This method is particularly suitable for highly viscous or viscous liquids, ensuring total sample transfer and minimizing waste.
Use special tips to handle viscous liquids
Wider hole tips
Wide-mouth tips are designed with a wider opening than standard pipette tips and are suitable for handling very thick solutions, gels or slurries. The wide mouth design reduces resistance when sucking or discharging viscous liquids, allowing for smoother flow and minimizing the chance of bubbles forming. This design is particularly beneficial when working with extremely viscous samples, where standard tips may become clogged or have inconsistent output.
Low suction tips
Made from a unique polypropylene material or coated with a hydrophobic substance, low-retention tips are the first choice when maximum sample recovery is required. These tips minimize the adhesion of liquid to surfaces, ensuring that virtually all of the aspirated volume is removed. This feature is particularly important when handling precious samples, ensuring minimal waste and optimal precision.
Filter tips
These tips have an integrated barrier or filter that prevents liquids, aerosols or any contaminants from entering the pipette. This design ensures sample purity and provides an extra layer of protection for the pipette from potential contamination or damage. In workflows such as PCR or when handling DNA/RNA, even minor cross-contamination can affect the results, so filter tips are indispensable.
Positive displacement pipette tips
These disposable pipette tips are uniquely designed with an integrated plunger. The piston is in direct contact with the liquid, bypassing the air cushion typical in standard pipettes. The result is precise and complete dispensing of even the most viscous or volatile liquids. For researchers working with highly heterogeneous or volatile samples, these pipette tips provide a reliable solution.
Extended suction tip
Extended pipette tips are longer than standard tips and are designed for easy access to the bottom of deep containers or test tubes. Extended tip length ensures aspiration and dispensing of the entire sample, minimizing dead volume and ensuring consistent results. Extended tips are particularly useful when working with deep well plates or long test tubes, where standard tips may not be able to aspirate the sample effectively.
Special material suction head
In addition to the standard polypropylene material, some pipette tips are made from materials targeted to specific liquid properties. Depending on their composition, these tips can offer benefits such as reduced static electricity, enhanced chemical resistance, or other special properties. Their application is related to the nature of the liquid or experimental requirements, ensuring that the tip material complements the characteristics of the sample to achieve optimal results.
