Temperature Considerations; Use Of Pipets And Graduated Cylinders - Hach DR/700 Procedures Manual

Temperature Considerations

For best results, most tests described in this manual should be performed
with sample temperatures between 20 °C (68 °F) and 25 °C (77 °F). If
certain tests require closer temperature control, that requirement will be
indicated in notes following those procedures.

Use of Pipets and Graduated Cylinders

When small sample quantities are used, the accuracy of measurements is
important. Figure 6 illustrates the proper way of reading the sample level
or the meniscus formed when the liquid wets the cylinder or pipet walls.
Figure 6 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 are long tubes with a series of calibrated marks to
indicate the volume of liquid delivered by the pipet. The calibrated
marks may extend to the tip of the pipet or may be only on the straight
portion of the tube. 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.
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