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capping the tubes or using a temporary push-cap or seal of the type supplied by Azenta Life Sciences for just such a purpose.
Additionally, it is important to ensure your labware defi nition in the set up program of the robot matches your tube or well geometry, and that the deck Z home point coordinate is accurately calibrated so that the liquid handling system can calculate the correct rate of descent for the tip as liquid is removed from the tube if using surface dispensing. When observing the tip move down the Z axis as it aspirates, it should keep a consistent distance between the bottom of the tip and the liquid surface. If this is not observed, the container defi nition may need to be adjusted. It is good practice for an automation engineer to test using material representative of their intended reagents (if possible) and liquid handling parameters which will be used in the method, to ensure everything is optimised.
It is possible to aspirate set amounts of a known volume and re-dispense back into the container to characterise a robust residual volume limit. Checking by weight before and after aspiration from a previously dispensed known volume is a widely used method for calculating dead volume in addition.
Recent work by a major tube manufacturer has shown that storage tube design can have an impact on residual volume. The work shows that in designing the best consumables to improve maximum sample aspiration, internal compound-curve tapers should be designed near the bottom of the tube to reduce total volume stored in this area whilst still allowing industry-standard pipette tips access to as near the bottom of the tube as possible.
of the inner well, but requires a minimum of 4mm internal diameter of the tube at that point.
Given most standard pipette tips for 10-1,000µl dispensing have less than a 2mm outer diameter at this point, it is self- evident that even with the tapered design of the new 1.6ml Tri-Coded Maximum Recovery Tube there will be no issues with automated liquid handling at 4mm above the bottom of the inner tube. There are clear benefi ts to the Maximum Recovery design. If the expected residual volume of the 1.6ml Tri Coded Tube is 50µl and the 1.9ml Tri Coded Tube is 210µl at the same Z-axis position in the liquid handler, one can compare the total amount of unrecoverable sample over a set number of storage tubes used.
Figure 3 shows the calculated amount of sample loss for the 1.9ml tubes over one hundred runs is equivalent to 21,000µl (21ml) compared to 5,000µl (5ml) with the 1.6ml tubes, resulting in a saving of 16ml over the same number of tubes. With expensive reagents, this can quickly accumulate into substantial savings.
We may conclude that it is imperative that lab managers considering a switch to automated liquid handling workfl ows should study the common variables and how to accurately measure the exact residual volume in their sample storage tubes using an automated liquid handler in advance, using their own experimentation and data from the robot and tube manufacturers.
Figure 1: Comparison between 1.9ml W.V rounded bottom tube & 1.6ml W.V. V-shaped bottom tube. Left - 1.9ml Tri-Coded tube (height in mm vs. volume in ml), Right -1.6ml Tri-Coded tube (height in mm vs. volume in ml).
In the comparison above, it can be seen that by creating a tapered internal wall at the bottom of the tube the total working volume is reduced for the same height (i.e. 15.8mm for 1.0ml volume vs. 20.1mm for 1.0ml volume) and at the same time this improves the shape for maximum sample recovery with a standard pipette tip.
Figure 2: Design comparison - 1.6ml Maximum Recovery Tube vs. 1.9ml standard Tri Coded Tube.
In this example, the total amount of residual sample volume left in the 1.6ml Tri-Coded tube would be as low as 50µl (3% of working volume) compared to 210 µl (12% of working volume) with the standard 1.9ml Tri- Coded tube when pipetting with an automated liquid handler that can go as low as 4mm above the bottom
Figure 3: Volume (µl) of Sample Lost per tube over one hundred cycles.
Producers are now starting to take into consideration design aspects that allow users to benefi t from reduced waste, not only to maximise the recovery of precious samples, but to save on reagent purchasing costs with a mind towards sustainable practices along the entire supply chain.
While the 1.6ml Maximum Recovery Tube from Azenta Life Sciences is the fi rst uniquely designed sample storage tube designed specifi cally for automated liquid handling, it is predicted that this will become one of a family of tubes manufactured to reduce dead volume and improve sample utilisation.
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