chemistries. Moving smaller amounts
of liquids precisely can often exceed the
capabilities of older pump technologies.
Most syringe and piston pumps use
stepper motors, which work by breaking
the motion down into discrete steps.
At high speeds, these steps are virtually
undetectable; however, at lower speeds,
the motor starts and stops in small steps,
which is known as “clocking.” When is
stepper motor is driving a pump, clocking
leads to pulsations in the flow, which can
create serious problems. High sensitiv-
ity sensors exposed to pulsations often
produce erroneous data. Pulsation can
also create “noise” that makes it difficult
to differentiate the sample results from
the background. In contrast, servo-mo-
tor-based drive trains like the ones used
in the latest syringe pump designs offer
smooth motion without clocking, even
at very low speeds, which translates
into non-pulsatile flow at low flow rates, Figure 2. Mounting a probe directly on the pump, as shown here, allows delivering small
volumes of liquid with high precision.