TriContinent C24000, Product Manual

Page: 133 / 144

Optimizing pump performance
C-Series Product Manual
133
Optimizing pump performance
There are two types of movements in a syringe pump, measured and
preliminary . Both are equally important in achieving optimum perfor-
mance.
• Measured movements provide accurate and precise fluid volumes to a
specified location.
• Preliminary movements prepare the fluid path for MEASURED move-
ments.
While most pump users are only concerned with the results of their
MEASURED movements, it is imperative to understand and fully utilize
PRELIMINARY movements if optimum pump performance is to be
achieved. One way to visualize the effect of PRELIMINARY movement in
the fluid path is to imagine trying to push or pull two bricks with an
inflated toy balloon between them. In order to get equal movement
between the bricks, you must either expand or compress the balloon to
its fullest point through preliminary movements. Once you have accom-
plished this, you have a
charged fluid path and MEASURED movements
will be optimized.
Air gaps are useful in minimizing mixing of aspirated and primed fluids
but must be handled carefully. Their introduction into a positive dis-
placement system can severely degrade precision and accuracy unless
countered with appropriate PRELIMINARY movements. AIR GAPS must
be kept as small as possible.
Even with air gaps between sample and priming fluids, some mixing will
take place in probes and tubes. In one-step sample dilutions, this has no
effect; but in multiple aliquoting and sample transfers, some dilution of
the measured sample closest to the air gap will occur. Make PRELIMI-
NARY allowances for some waste if absolute sample integrity is
required. Aspirate an additional amount of the sample to act as a buffer.
Discard this amount as part of the probe cleaning process. Typically 10%
can be used as a guideline, but variables such as speed, type of fluids,
volumes, and allowable error will determine final adjustments. Optimum
waste allowances can only be determined through testing.
Repetitive functions, such as multiple dispenses and aliquoting, are best
done when all MEASURED movements are done in a like manner and
speed. PRELIMINARY movements to ensure a CHARGED fluid path are
critical to achieving optimum precision. The best method for accom-
plishing this task is to make a PRELIMINARY dispense, roughly equal to
the desired MEASURED movement, of the aspirated fluid into a waste
cup or even into the same receptacle aspirated from, if possible.
Backstepping or anti-backlash routines built into most commercial
syringe drive software typically eliminate only the inherent looseness of
the drive mechanism. They do not CHARGE the fluid path.
Priming, the most common PRELIMINARY movement, is important. All
air should be expelled from the syringe, valves, tubes, and other wetted
surfaces to achieve optimum performance.
Bubbles and air pockets may cause inconsistencies. Small bubbles
located directly on the surface of the syringe seal often do not cause
problems. However, should they break free and enter the fluid path, a
MEASURED movement could be affected. It is best to try and remove
these through adequate priming. Surfactants in priming fluids make