
UltraMicroPump II
WORLD PRECISION INSTRUMENTS 5
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.