WPI UltraMicroPump II Instruction Manual page 7

UltraMicroPump II
Choosing a Syringe
the syringe should be chosen to inject no less than 5% of the volume of any given
syringe.
Example: A 100 µl syringe may be used for injections on the umPii to volumes of
5 µl (5000 nl) and higher with high precision and repeatability. expecting this 100
µl syringe to inject lower than 1 µl may be difficult if the syringe is not calibrated
specifically on the pump. the overall accuracy of the syringe itself is usually no
greater than +/-3% and the syringe internal diameter may deviate from location to
location along the length of the syringe interior.
choosing the correct syringe for an injection is a very important consideration,
due to accumulated errors of the syringe and the pumping method. For a 1000 nl
injection from a 10 µl (10,000 nl) syringe, the user is asking for a 1/10th the
syringe's volume value to be injected. theoretically, based on mathematics without
any consideration to surface tension, heat, pressure, compressibility, silanization,
or air bubbles, the 3% error rate should yield a ± 300 nl variance.
As a rule of thumb, the choice of the syringe should not exceed 1/10th to 1/20th the
stated full volume of the syringe. the micro4-umP2 system uses a stepper motor
to move the syringe piston forward to inject the volume. A consideration should
also be made to allow the motor to step forward a good number of steps to prevent
errors in volume injecting.
Example: in the 10 µl case above, a 1-step movement of the motor will inject
a volume of 0.5276 nl. For two steps to occur, a volume of 1.055 nl will be
injected. this may or may not be acceptable as the total error may exceed 1
nl or nearly 0.1%. Also note that two steps is probably not enough resolution to
accurately control the volume; another rule of thumb would be to step no less than
10-100 steps for the entire single injection. using this 10-step rule, the minimum
acceptable injectable volume from this 10 µl (10,000 nl) syringe would be
0.527.6 nl × 10 or 5.276 nl. other syringes will give other results, due to the inside
diameter and the volume per step.
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