18.104.22.168. Using Pipets.
Pipets are used to accurately measure a volume of liquid and then to transfer it to a vial or other container. There are
two general types of pipets in the WQAS-PM: dropping pipets and standard volumetric pipets (including one micro
Use: Dropping pipets are found in several of the individually packaged test kits within the WQAS-PM.
They are simply eyedroppers with a liquid-level line marked on them. They are used to measure and
transfer liquid when only a reasonable amount of accuracy is necessary. They are also used to add
reagents to a solution drop by drop (titrating).
Drop Size: The size of a drop from a dropping pipet may vary depending on how the dropper is held. For
accurate results with the WQAS-PM drops should be kept the same size. Two things are most important in
producing drops of the same size.
The angle at which the dropper is held: The dropper should be held vertically, that is straight up and
down, when expelling drops.
How hard the rubber bulb is squeezed: The rubber bulb should be squeezed firmly, slowly, and
steadily, until a drop is formed at the tip and falls into the container. Some practice is required to be
able to consistently produce drops of the same size.
Standard Volumetric Pipets: Volumetric pipets are used to measure and transfer liquids when great accuracy is
needed. There are three volumetric pipets in the WQAS-PM. They are found in the main carrying case. Use of all three
Rinse: Rinse the pipet two or three times with the sample to be tested before filling. Always use a pipet
filler to draw the sample into the pipet (fig. 24).
Never pipet chemical solutions or water samples by mouth. May be harmful if swallowed. Use
the pipet filler. In the event a reagent is accidentally swallowed, follow the directions in the
warning statement for that reagent.
Fill: Fill the pipet(l) using the pipet filler(2). The pipet filler is a rubber bulb with several valves. It is used
to draw liquid into the pipet and to expel the liquid into a container. It is used as follows:
Figure 2-4. Using the Pipet Filler.
Insert the pipet(l) into the tube on the pipet filler(2) containing Valve S(3) until it is firmly seated. If
necessary use a twisting motion to firmly seat the pipet(l) within the tube.
Squeeze Valve A(4) while squeezing the rubber bulb. Lower the tip of the pipet(l) into the liquid.