Hach DR/850, Procedures Manual, Page: 27 / 460

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CHEMICAL ANALYSIS INFORMATION
, continued
Figure 3 Reading the Meniscus
Rinse the pipet or cylinder two or three times with the sample to be tested
before filling. Use a pipet filler or pipet bulb to draw the sample into the
pipet. Never pipet chemical reagent solutions or samples by mouth. When
filling a pipet, keep the tip of the pipet below the surface of the sample as
the sample is drawn into the pipet.
Serological pipets have marks that indicate the volume of liquid delivered
by the pipet. The marks may extend to the tip of the pipet or may be only
on the straight portion of the tube. If the marks are only on the straight
part of the tube, fill serological pipets to the zero mark and discharge the
sample by draining the sample until the meniscus is level with the desired
mark. If the serological pipet has marks extended to the tip of the pipet,
fill the pipet to the desired volume and drain all the sample from the pipet.
Then blow the sample out of the pipet tip for accurate measurements.
Volumetric (transfer) pipets have a bulb in the middle and a single ring
above the bulb to indicate the volume of liquid when it is filled to the
mark. To discharge a volumetric pipet, hold the pipet vertical until only a
small amount of liquid remains (about ¾ inch), then hold the pipet at a
slight angle against the container wall to drain. Do not attempt to
discharge the solution remaining in the tip of the pipet after draining.
Volumetric pipets are designed to retain a small amount of sample in the
pipet tip.
If sample drops stay on the walls of the pipet, the pipet is dirty and is not
delivering the correct amount of sample. Wash the pipet thoroughly with a
laboratory detergent or cleaning solution and rinse several times with
deionized water.
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