Reading the Meniscus
Pipets and Cylinders.
Rinse the pipet or cylinder two
or three times with the sample to be tested before filling.
safety pipet filler to draw the sample into the pipet.
When filling a
pipet, keep the tip of the pipet below the surface of the sample as
the sample is drawn into the pipet, or you will lose the suction and
possibly introduce surface particles.
(1) Serological Pipets.
Serological pipets are long tubes
with a series of calibrated marks to indicate the volume of liquid
that will be delivered by the pipet.
The calibrated marks may extend
to the tip of the pipet may only be on the straight portion of the
Fill serological pipets to the zero mark and discharge the
sample by allowing the sample to drain until the meniscus is level
with the desired mark.
If the serological pipet has calibrated marks
extended to the tip of the pipet, the sample must be blown out of the
tip for accurate sample measurements.
(2) Transfer Pipets.
Transfer pipets are long tubes with a
single ring to indicate the volume of liquid that will be delivered
when it is filled to the mark.
To discharge the sample from a trans-
fer pipet, hold the tip of the pipet at a slight angle against the
container wall and allow the sample or reagent solution to drain.
Do not attempt to discharge that portion of the sample of reagent
that remains in the tip of the pipet after draining.
are manufactured so that a reproducible amount of sample always
remains in the tip of the pipet.
(3) The Rubber Bulb Pipet Filler.
There are several types which
may be used.
The rubber bulb assembly can be used as illustrated
Insert the pipet into the sample; depress the bulb;
restrict the intake end of the rubber tubing and release the bulb.
Observe the pipet to ensure that the direction of suction is