Sterilab Guide to Reducing Pipetting Errors
LEARN TO PIPETTE LIKE A PRO!
BACKGROUND
Even the most experienced scientist can sometimes do with a reminder of good practice in pipetting, so we have put together the following quick hints, tips and reminders to improve your pipetting technique.
Better results start with the correct technique, and by spending a little time training the team you can ensure that everyone is consistent in their approach. The smallest of changes can make a great difference even to the most accomplished professionals.
Sterilab’s top recommendations for pipetting practice:
OPERATOR PROFICIENCY
Documentation to prove operator proficiency. Identify the skills of your team and ensure that an up-to-date training and proficiency schedule is maintained. Remember, online and physical training can be combined.
VOLUME OF PIPETTE
Picking the correct instrument for the task is key! Select, the correct volume of pipette. Use the pipette that will dispense the volume in one go, and do not use a pipette that you need to use 2-3 times to achieve the required volume.
DEPTH - IMMERSION
Whether it is over- or under-immersing, the correct immersion of the tip can improve accuracy by up to 5%. The correct immersion is 1-2mm for micro volume and 3-6 mm for normal range. Too much liquid can be aspirated if the volume of gas in the tip is compressed.
PIPETTING ANGLE
Pipetting correctly is all about getting the right angle. The angle of the pipette can make all the difference, so place the pipette 10-45° against the inside wall of the receiving vessel and wait for a second before aspirating.
RHYTHM AND SPEED
As with everything, consistency is the key. Employing the same rhythm and speed will ensure that samples are aspirated in the same manner every time, whereas a jerking action can cause spillage.
PRE-RINSING / WETTING
Remember to pre-rinse new tips. This is a speedy way to increase accuracy and to ensure the same volume consistently dispensed. Dispelling liquid from a pipette leaves some residual coating on the tip, therefore pre-rinsing will stop the expelled liquid being less than required. The dosing of the liquid from a pipette leaves a liquid coating on the tip, which causes the dispensed volume to be slightly lower than it should be. Pre-rinsing a new tip a couple of times, at least, with the liquid that is going to be used, will serve to condition the inside of the tip.
INSTRUMENT CARE
An operator is only as good as their tools. Ensuring that pipettes are correctly cleaned and cared for not only increases accuracy, but also has an environmental impact on the laboratories usage of plasticware by reducing the need to replace pipettes. Daily cleaning can ensure that samples are not contaminated – it is recommended that pipettes are cleaned with 70% ethanol.
ERGONOMICS
Choose a pipette that is lightweight and comfortable to use. Keep the wrists straight and in a neutral pose. Relax and employ a comfortable hold without over-gripping the pipette. Use a support in between use if needed and pipetting tasks can be repetitive.
TEMPERATURE
Pay attention to the temperature of the solution being pipetted, and remember that the calibration of pipettes is done at room temperature. Working with liquids that are significantly higher or lower than this will alter the accuracy of your pipetting. An increase or decrease in temperature can cause thermal expansion or shrinking, as a point to remember when liquids are colder they become more dense whereas warmer liquids the opposite, compared to room temperature liquids.
STORAGE
Pipettes should be stored in an upright position on supports which are designed for them (if available).
TIPS
Use the correct size tip for the pipette and ensure that it has been manufactured to a high level - a universal fit tip may be a good choice. Ensure that you check the tip before aspirating the sample. Tips and pipettes work together as a system. Remember, tips are single use and are not designed for multiple transfers, this can cause contamination and also inaccuracies in volumes.
CALIBRATION
It is an annual requirement to calibrate your pipettes but advisable to do this a little more often, perhaps every three months for instruments that have a heavy usage. Calibration will ensure that you are dispensing the correct amount of sample every time.
AIR ASPIRATION
This is one of the most common pipetting errors. It may seem the most common sense, however, paying attention to the air being sucked up can not only cause air to enter the liquid (causing air bubbles) but also cause the volume pipetted to be inaccurate due to the air entering the neck of the pipette.
USE A PIPETTING MANAGEMENT SYSTEM
Using a pipetting ID system (such as the PlatR) can reduce the likelihood of errors and will remember your pipetting plan. This will ensure that samples are correctly pipetted into the correct well every time and reduce the likelihood of sample contamination.
Learn how we can help with your Laboratory Consumables, get in touch with Sterilab and we will put you in touch with our Specialist Consumables Manager.