You have a favorite pipette. Familiarity with the electronic interface makes its use second nature. Maybe your hand fits it just right, or the smoothness of the action makes it easy to use. Then, one day, your dispensed volume just feels “off”. You try pipetting the liquid again, and again it looks too low or too high. What can you do? Basic pipette testing verifies the accuracy – or inaccuracy – of your equipment.
Fortunately, you can perform basic pipette testing with a few pieces of lab equipment. Let’s get started.
Collect the following equipment and supplies.
- A weighing device. Balances offer more precision, but a digital scale can suffice for larger volume samples.
- A weighing vessel, such as a beaker.
- A steady and consistent pipette technique.
- An environment with stable temperature and humidity.
- A stable surface.
- Distilled water.
Pipette Testing Preparations
Once you collect the needed items, start by setting up your weighing device on a stable surface in an environment with minimal temperature and humidity variations. If your scale or balance has a leveling bubble and internal calibration, utilize both now. Finally, set your weighing device to read grams.
With your scale or balance ready, place your weighing vessel on the weighing device and either “tare/zero” the unit or record the weight of the vessel to be subtracted from your overall weight later.
Pipette Testing Procedure
With all the preparations made, set the pipette’s volume to the middle of its range. Draw up a sample of water and dispense it into your weighing vessel. The elegance of this procedure lies in the near-perfect conversion of microliters of distilled water to grams of mass. This conversion involves nothing more than moving the decimal three (3) places. To go from grams to microliters, move the decimal to the right. To from go from microliters back to grams, move the decimal to the left.
For instance, fifty (50) microliters of water weighs 0.05 grams: a movement of the decimal from 50.0 three places to the left to 0.05. Similarly, .0485 grams of distilled water translates to 48.5 microliters of water: a movement of the decimal from 0.0485 three places to the right, to 48.5.
So, when you verify a pipette with a range of 10-100 microliters at 50 microliters and the balance reads 0.0487g, then your pipette dispensed 48.7 microliters. If your scale or balance does not have a zero or tare function, subtract the weight of the vessel from the total measured weight after dispensing the water. After verification at the mid-range, set the pipette’s range for its lowest and highest settings and repeat the procedure for the respective ranges.
While this method does not yield the precision results of more in-depth procedures, it provides you with a general idea of pipette performance and accuracy. With that in mind, let’s say you’ve figured out that your pipette is reading too far out of range to be used within your lab. What do you do now? Throw the pipette away and buy new?
Of course not! Send it to the professionals at Precise Technical Solutions. The diagnosis, repair, and calibration of lab instruments such as pipettes forms a core part of our team’s competencies. With a little time in our lab, our technicians will have your favorite pipette operating just like it did the day it was new.