Processing kodak motion picture films, module 3 analytical procedures

In observing the lowest point on the meniscus it
is very important that the line of vision be in the
same horizontal plane as the bottom of the
meniscus. This is easily ascertained if the
graduations on the glassware extend at least
halfway around the tube. The eye is correctly
positioned when both front and back portions of
the graduation coincide (Figures 1 and 2). The
meniscus may be seen more clearly if a small
white card with a rectangular black patch is held
behind the meniscus. Raise or lower the card
until the bottom of the meniscus is clearly
outlined (Figure 3).
Figure 3 Outlining the Meniscus
F002_0904AC
2. Pipets
Pipet specifications are established on the basis of a
pipet's ability to deliver (TD) a known volume of
distilled water (20°C [68°F]) within the specified
tolerances. Pipets meeting the volume shown in
Table 1 have been used successfully. The pipets
conforming to these requirements are defined as
“Class A.” However, experience has shown that some
pipets marked “Class A” do not meet delivery time
specifications. Other pipets having shorter delivery
time than “Class A” meet “Class A” volume
tolerances. Pipets meeting “Class A” volume
tolerances but not meeting delivery time requirements
may be used for analytical purposes as long as the
analyst understands and practices the following
instructions on the use of pipets:
a. Cleanliness
Use a clean pipet. The pipet does not have to be
dry, but must be perfectly clean and free from
grease so that drops of the solution will not
adhere to the walls, causing the pipet to deliver
less than the rated volume. Any contaminant
may affect the results.
b. Perfect Tip
Use a pipet with a perfect tip. A pipet with a
broken or chipped tip must be discarded since it
will deliver a volume other than the rated
volume when the tip is touched against the wall
of the receiving vessel.
c. Rinsing (or Seasoning)
With one hand holding the pipet and the other
hand holding a rubber bulb, squeeze the bulb,
place it over the upper end of the pipet and
release slowly. Draw a small portion of the
solution into the pipet, i.e., about 20 percent of
the volume of the pipet, then remove the bulb
and cap the pipet with the forefinger. See
Figure 4. Place the pipet in a horizontal position,
and rotate it, permitting the solution to wet the
walls to a point about two inches above the
calibration mark. Do not permit the top of the
mouthpiece to become contaminated with
solution, which in turn may contaminate the
bulb. Discharge the solution through the tip, and
repeat the rinsing with another portion of the
solution.
Note: If the solution being pipeted is a
standardized reagent, the reagent is drawn into
the pipet from a clean beaker which was rinsed
once with reagent. To prevent contamination of
the reagent, the pipet should not be placed into
the stock bottle.
Figure 4 How to Use a Rubber Bulb for Pipeting
B. Release bulb and liquid will
be drawn up slowly. If suction
ceases before pipet is full,
remove bulb, recompress,
and reapply.
F002_0905GC
A. Dip pipet tip into liquid.
Compress rubber bulb in left
hand, and slip bulb over end
of pipet.
C. When liquid rises above
calibration mark, remove bulb
and place index finger of right
hand to end of pipet.
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 3