The micropipette is an instrument of daily use in laboratories, so preventing contamination in pipetting is essential to achieve reliable results. Therefore, it is necessary to know how to identify potential contamination factors capable of altering the precision and quality of these results.
The first step to avoid contamination in the laboratory environment is the correct use of the personal protective equipment (PPE) recommended for each type of routine. The most used are:
- Protective goggles
- Protective footwear
Laboratory benches are a good place for bacteria, due to the fact that several different products and objects pass by each day. When some dirt gets encrusted on the bench, the chance of the sample being handled there being changed in pipetting is great. Therefore, it is important to keep these surfaces regularly cleaned. Each laboratory works with different samples, so it is important that the site is cleaned according to the routine done there. The products most used in laboratory bench cleaning are water, bactericidal soap, 70% alcohol and sodium hypochlorite (bleach).
TYPES OF CONTAMINATION IN PIPETTING AND HOW TO AVOID THEM
Suspensions of solid or liquid particles in a gas or aerosols are formed in many laboratory activities, mainly with the use of air displacement pipettes. And these aerosols are one of the main contamination factors in pipetting. For example, they can be transferred into the micropipette when using tips without a filter, causing contamination in subsequent samples. Check out the most frequent contaminations in a laboratory below:
Pipetting: micropipette contamination – sample
It results from the use of a contaminated micropipette or non-certified tips. In this way, contamination of the sample in pipetting can be avoided with the use of sterile tips, cleaning or autoclaving the micropipette.
The tips have three categories between degrees of purity:
- without purity certification
- contaminant-free certificate like DNase, RNase and endotoxins
- sterilized free of microbial life
Contamination of the sample micropipette can be avoided by following a few guidelines:
- Select a tip with the purity class relevant to your application
- Use sterile tips with filter or positive displacement tips. Alternatively, it is also possible to use filters on some brands of micropipettes. Thus, filters prevent aerosols from reaching the micropipette body, being a potential factor in the contamination of subsequent samples.
- Always change the tips after each sample
- Autoclave or regularly clean the pipette and other components that may come in contact with the sample
Pipetting: sample contamination – micropipette
It occurs when the sample or its aerosol particles enter the micropipette body at the time of pipetting. Therefore, to minimize this risk of contamination, some steps must be followed:
- Always hold the micropipette in an upright position during the procedure and store it upright. This prevents liquids from leaking and contaminating the equipment
- It is recommended to immediately eject the tip after use to prevent the entry of aerosols
- Release the micropipette button slowly to avoid aerosol formation and sample spills inside the equipment
- Use filter tips or positive displacement tips to avoid transferring the aerosol to the micropipette
Sample contamination for the micropipette
Pipetting: Sample – sample contamination
Sample to sample contamination (or contamination by transport) occurs when the aerosol or liquid residue from one sample is transported to another. This occurs when the same tip is used multiple times. Like this:
- Always change the tip after each manipulation
- Use filter tips or positive displacement tips to prevent the sample aerosol from passing through the micropipette body and contaminating the next sample
- If you suspect contamination of the micropipette, autoclave or clean the equipment according to the manufacturer’s instructions
HOW TO DECONTAMINATE YOUR MICROPIPETTE
Before applying any of the guidelines, check that the micropipette material is compatible with the cleaning solutions shown below.
|Causes of Contamination||Decontamination Techniques||Cleaning Guidelines|
|Radioactive compounds||Detergent – cleaning solution||Disassemble the bottom of the micropipette. Completely immerse contaminated parts * in an ultrasonic bath with detergent or cleaning solution recommended for laboratory instruments. It is highly recommended to rinse several times with water. Dry well.
Always check that the radioactivity has decreased to an acceptable level.
|Viruses, bacteria, mycoplasma , fungi||UV radiation||Work surfaces can be decontaminated by exposure to 300 nm of UV light for 15 minutes. Note that UV rays cannot penetrate inside the micropipette and cannot be considered as a decontamination protocol for components.|
|DNA, RNA, biological samples||3% hypochlorite solution or UV radiation||Disassemble the bottom of the micropipette. Completely immerse contaminated parts * in 3% sodium hypochlorite for 15 minutes. Rinse well with distilled water and dry. Exposure to UV light for 30-60 minutes will further reduce DNA contamination, but does not eliminate it entirely from the pipette surface.|
|Aqueous solutions and buffers||Cleaning with water||Disassemble the bottom of the micropipette. Wash contaminated parts thoroughly with distilled water and dry.|
|Acids / alkalis|
|Organic solvents||Detergent – cleaning solution||Disassemble the bottom of the micropipette. Completely immerse contaminated parts * in an ultrasonic bath with detergent or cleaning solution recommended for laboratory instruments.
Wash the micropipette several times with water and dry it well.
* Refer to the Instructions for Use for specific parts for immersion cleaning.
Some micropipettes can be fully autoclaved or only parts that have been contaminated due to improper use.
Air displacement pipettes and some tips are normally autoclaved at 121 ° C with a positive pressure of 1 bar (100 kPa) over a period of 20 minutes.
- Remember: filter tips should not be autoclaved. Instead, it is recommended to use sterile products.
After autoclaving, micropipettes or autoclaved parts should dry completely and cool to room temperature. As heated plastic parts can easily stretch or damage, micropipettes should only be screwed in again after they have cooled completely.