Page 45 - Modern Analytical Chemistry

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28 Modern Analytical Chemistry

(c) (d)

Figure 2.5
Common types of pipets and syringes: (a) transfer pipet; (b) measuring pipet;
(c) digital pipet; (d) syringe.
Photos courtesy of Fisher Scientific.
(a) (b)

pipets, delivery of the calibrated volume requires that any solution remaining in
the tip be blown out. Digital pipets and syringes can be used to deliver volumes as
small as a microliter.
Meniscus Three important precautions are needed when working with pipets and
Calibration volumetric flasks. First, the volume delivered by a pipet or contained by a volu-
mark
metric flask assumes that the glassware is clean. Dirt and grease on the inner
glass surface prevents liquids from draining evenly, leaving droplets of the liquid
on the container’s walls. For a pipet this means that the delivered volume is
less than the calibrated volume, whereas drops of liquid above the calibration
Figure 2.6 mark mean that a volumetric flask contains more than its calibrated volume.
Commercially available cleaning solutions can be used to clean pipets and volu-
Proper means of reading the meniscus on a
volumetric flask or pipet. metric flasks.