Practical Tips for the Care and Use of Pipettes
Using a pipette is a part of normal routine in a typical science laboratory. You need a pipette whether you are doing a biuret test, diluting a stock solution or purifying plasmid DNA. This essential and highly precise lab instrument needs to be handled with extreme care, maintained well and calibrated on a regular basis.
Whether you are using a micropipette or a graduated pipette, always hold the pipette in a vertical position. Try not to deviate more than 20 degrees from vertical. A horizontal position may cause an incorrect amount of liquid to be drawn.
For accuracy and ease of use, choose the correct pipette based on the volume that will be dispensed. When using a fixed volume pipette, pick one with the desired volume. When selecting a variable volume micropipette, the most commonly used one, you need to pick one that has the correct volume range. For example, a 5000 µl micropipette is not the right choice for a 150 µl sample.
When you are pipetting an aqueous solution use an air-displacement pipette. When you are pipetting a viscous, volatile or corrosive solution use a positive-displacement pipette. Aspirating and dispensing steps vary based on the type of the pipette. Please follow the instructions provided by the manufacturer.
Ensure that you use a correct tip for your pipette. Do not touch the pipette tip. Re-use the tip only if you are dispensing the same reagent into separate tube(s). If you are dispensing a different reagent, you have to use a new tip.
A graduated pipette has graduation markings indicating volume along its body. It is used to transfer liquid in milliliter range, from 1 ml to up to 50 ml. It can be glass or plastic (disposable).
Regardless of the type of pipette, always use a pipette-aid for drawing up the solution. Never use suction through your mouth to fill a pipette—it is very dangerous, since you may accidentally swallow the solution. Many different pipette aids are available that can help you safely draw the solution into your pipette. There are tri-valve, syringe and electronic pipette aids designed to fit into all types of graduated pipettes.
Always hold your pipette upright and do not touch the pointed tip. When you are filling the pipette, you will notice that the solution will form a meniscus. If the solution has a high viscosity, measure the volume by looking at the upper meniscus. If the solution has a low viscosity, measure the volume by looking at the lower meniscus. Always focus on the center of the meniscus to ensure the best volume measurement.
You can use a common cleaning agent such as soap, mild detergent or alcohol to remove the dust or dirt on the outside of your pipette (micropipette or glass pipette).
Cleaning the inside of a graduated glass pipette can be done by soaking and flushing in detergent or distilled water. If there is a laboratory glassware washer, you can use it to wash your graduated glass pipettes.
Cleaning the inside of a micropipette can be tricky since individual parts will need to be cleaned differently based on the part. Ideally, follow the steps in the instruction manual.
If your pipette is contaminated, you will need to use a specific solution to clean it.
- Aqueous solutions, inorganic solvents or buffers: Use 70% alcohol to rinse the contaminated part and air dry at 60-70°C.
- Organic Solvent: The solvent will evaporate on its own. Alternatively, you can wash with a detergent and air dry at 60-70°C.
- Radioactive Substances and Proteins: Use a strong detergent and rinse with distilled water several times. Then air dry at 60-70°C.
- Nucleic Acids: Boil the lower parts of pipette in glycine/HCl buffer for 10 minutes. Rinse with distilled water several times. Then air dry at 60-70°C.
Calibration of a pipette must be done regularly, depending on the frequency of the use and application. Annual calibration is recommended. If the pipette is used on a daily basis, calibration should be done more often, such as every 3 months. Since a micropipette is sophisticated lab instrument, it is better to send it in for service rather than calibrating it yourself.
It is easier to calibrate a glass pipette than a micropipette. It can be done by using distilled water, thermometer, beaker, balance and weight boats. For details, watch this short YouTube video.
When not in use, pipettes should be properly stored. For micropipettes, pipette stands are ideal storage options. Keep the pipettes in an upright position, tips removed, set at the highest volume and away from heat/moisture. For graduated pipettes, you can use storage racks, boxes or designated drawers as safe storage options.
I hope this information will help you maintain the accuracy and performance of your pipettes.