In the biological laboratory, researcher Xiao Zhang was about to use a pipette to absorb the sample, and the instructor next to him reminded him: "Rinse the tip first before operating." This seemingly simple step is related to the accuracy of the experimental results. Do pipette tips need to be pre-wetted? How to choose in different experimental scenarios? This article will start from the principles, operating specifications, experimental types, etc. to reveal the scientific logic behind this basic operation, helping scientific researchers and laboratory newcomers avoid error traps.
Contents
1. Why should we consider wetting the tip? Core principle analysis
2. Which experiments must rinse the tip? Three typical scenarios
3. The correct posture for rinsing: operating steps and precautions
4. Applicable situations for non-rinsing: two special scenarios
5. The risk of improper rinsing: error cases and consequence analysis
6. Answers to common questions: detailed control from material to frequency
1. Why should we consider wetting the tip? Core principle analysis
1. Surface tension and adsorption effect
When the material of the inner wall of the tip (such as polypropylene) comes into contact with the liquid, surface tension and adsorption will be generated. Taking water as an example, when the first pipette is sucked, about 0.5-1μL of liquid remains and adheres to the inner wall of the pipette tip, resulting in a smaller actual pipette volume.
Experimental data: A laboratory test shows that the error of transferring 10μL of liquid without rinsing the pipette tip can reach 8%-12%; after rinsing 3 times, the error is reduced to less than 1%.
2. Differences in solution affinity
Different solutions have different affinities with pipette tip materials:
Strongly adsorbable liquids: such as protein solutions and nucleic acid samples, are easy to adhere to the inner wall of the pipette tip, and rinsing can reduce losses;
Low surface tension liquids: such as isopropanol and ether, rinsing can reduce volume deviations caused by volatilization.
3. Temperature and humidity effects
Environmental factors can change the physical properties of liquids:
High temperature environment: Liquid evaporates quickly, rinsing can form a protective film on the inner wall of the pipette tip, reducing volatilization during subsequent pipetting;
High humidity environment: The pipette tip is prone to condensation of water vapor, affecting the accuracy of pipetting, and rinsing can remove potential interference.
2. Which experiments require rinsing the pipette tip? Three typical scenarios
1. Micro-pipette (<10μL)
Risk analysis: Micro-liquids are significantly affected by the adsorption effect, and the error may exceed 15% when not rinsing.
Case: In a PCR experiment, 2μL of enzyme solution was transferred without rinsing the pipette tip, resulting in a 40% decrease in amplification efficiency and invalid experimental results.
2. High-value sample operation
Scenario examples: precious clinical samples, radioactive markers, rare cell suspensions.
Operation specification: After rinsing 3 times, rinse with the sample once (to avoid cross contamination) to ensure that every drop of liquid is used to its full potential.
3. High-precision quantitative experiment
Typical experiments: ELISA, HPLC sample pretreatment, standard curve drawing.
Data comparison: In a drug concentration determination experiment, the CV value (coefficient of variation) of the rinse group was 3%, and that of the non-rinsed group was 8%. The latter data is not recognized by the journal.
3. Correct posture for rinsing: operation steps and precautions
1. Standard operation procedure
① After installing the pipette tip, absorb 3-5 times the liquid range;
② Slowly discharge to the waste tank, repeat 3 times;
③ If processing special samples, rinse with the sample once at the end (new pipette tips need to be replaced to avoid contamination);
④ Keep vertical when pipetting, and aspirate at a moderate speed (too fast to easily generate bubbles).
2. Common error demonstrations
Over-rinsing: More than 5 times may introduce additional errors (such as dilution caused by liquid residue);
Randomly discarding liquid: The rinsing liquid is not discharged into the designated waste tank, causing biosafety hazards;
Mixed pipette tips: Failure to distinguish between ordinary pipette tips and filter pipette tips affects the rinsing effect.
3. Key points for tool selection
Filter pipette tips: Suitable for nucleic acid and protein experiments to prevent aerosol contamination, but it is necessary to ensure that the filter element is not blocked during rinsing;
Low adsorption pipette tips: Essential for handling viscous liquids (such as glycerol), although the adsorption is reduced, rinsing is still required.
4.Applicable situations for non-rinsing: two special scenarios
1. Volatile organic solvents
Principle: rinsing will accelerate the evaporation of solvents, resulting in concentration changes.
Alternative solution: use an airtight pipette and absorb 10% more volume for the first aspiration (to compensate for evaporation losses).
2. Large batches of the same sample operation
Scenario description: such as 96-well plate loading, repeatedly pipetting the same solution.
Operation skills: After rinsing the first well, the subsequent wells are directly pipetted (provided that the solution properties are stable and there is no risk of cross-contamination).
5.Risks of improper rinsing: error cases and consequence analysis
1. Experimental result deviation
Case 1: In the cell culture experiment, the failure to rinse the pipette tip resulted in a low cytokine concentration and a misjudgment of the cell proliferation rate;
Case 2: When testing environmental water samples, the rinsing solution was not completely drained, resulting in a false increase in the concentration of the target pollutant.
2. Cost and time waste
Data: A pharmaceutical company failed a batch experiment due to a mistake in rinsing, resulting in a direct loss of 20,000 yuan in consumables and a 15-day delay in the R&D cycle.
3. Biosafety hazards
Risk point: After rinsing samples containing pathogens, the pipette and countertop were not disinfected in time, causing laboratory contamination.
6.FAQs: Detailed control from material to frequency
Q1: Do all pipette tips need to be rinsed?
A: Due to the special structure of the filter tip, the number of rinses can be reduced to 2 times; ordinary pipette tips require 3 times.
Q2: How to control the frequency of rinsing?
A: When changing the solution, switching the sample type, or not using it for more than 30 minutes, you need to rinse again.
Q3: How to rinse in high-temperature experiments (such as hot-start PCR)?
A: First preheat the pipette tip to the reaction temperature (such as a 60°C water bath), and then rinse with the preheated solution to avoid volume errors caused by temperature differences.
Q4: Can pure water be used instead of sample rinsing?
A: It is only applicable to non-viscous, non-biologically active buffers. Sample rinsing is required when handling samples such as proteins and nucleic acids.
Summary
Pre-wetting of pipette tips is a typical example of "details determine success or failure" in the laboratory. For micro-volume, high-precision, and high-value sample experiments, rinsing is a necessary step to ensure reliable data; while in volatile liquids or large-scale repeated operations, flexible adjustment strategies are required.
Remember three principles:
Rinse on demand: choose whether to rinse and the number of times according to the nature of the sample and the accuracy of the experiment;
Standard operation: follow the "absorb-discharge-absorb" process to avoid cross contamination;
Dynamic adjustment: timely evaluate the necessity of rinsing when the environment changes (such as temperature and humidity fluctuations).
As a senior experimenter said: "Behind a precise pipette is a thousand times of respect for details." Next time you pick up a pipette, spend 10 more seconds rinsing - this may be the key to the success of the experiment.