CLINICAL LAB SCIENEC

CHAPTER 8: PIPETTING AND USE OF GLASSWARE 187
for pipettes, the tolerance level may be etched or stamped onto the devices. So
depending on the intended use, a piece of glassware may be made of varying
grades of glass. Where accuracy to a great degree is not required, it is possible to
use pipettes and other glassware that are not accurate beyond a minimal standard.
Some pieces are more suitable for heating, and others are designed to be
disposable due to the materials used in their manufacture. Laboratory plastics
might still be called glassware and are often used to replace the actual glassware
used in the clinical laboratory. Plastics are highly flexible, somewhat inexpensive,
and easily disposed of following use. The drawbacks of plastics are due to the
use of large amounts of scarce petroleum products for their manufacture and
the need for special handling for the safe disposal of some types. Toxic fumes
emitted when plastics are burned may be hazardous to the health of humans as
well as wildlife. Some work is being done on biodegradable plastics that will not
create environmental contamination.
For safety, it should be noted that glass and plastics that are in direct contact
with biohazardous materials are most often disposable. In addition, plastic containers
may not break if dropped on a hard surface, but actual glass will almost
always break in a laboratory accident, requiring the cleanup of toxic materials
in many cases. A number of plastics are manufactured for laboratory practice,
and each is practical for certain procedures. The major types of plastics used in
a laboratory are polystyrene, polyethylene, polypropylene, Tygon, Teflon, polycarbonate,
and polyvinyl chloride.
Use and Cleanliness of Plastic versus Glass
Both plastic and glass supplies may require special handling when they are being
cleaned. Rinsing glass or plastic supplies after they are used and then washing
with detergent designed for cleaning laboratory supplies, followed by rinsing
with distilled water, may be sufficient in many instances. Detergents and temperature
levels of water for washing the supplies must be compatible with the material
from which the supplies are constructed. Glass is required for some procedures
while plastics are sufficient for others, depending upon the potential for absorption
of chemicals and damage that may occur to the containers when exposed to
various chemicals. Plastics may break down when exposed to harsh detergents,
so these are considerations to be heeded when washing laboratory supplies. Both
plastic and glass containers, tubes, and pipettes should appear spotless on visual
inspection if an acceptable process of cleaning was followed.
Although pipettes, both serological and volumetric, are usually disposable,
some laboratories find it useful to wash certain pipettes. Pipettes are washed in
special cylindrical washers, if it is necessary to wash them. The ends of the pipettes
with the smaller openings are placed toward the top of the wash cylinder and the
ends with the larger openings are positioned toward the bottom to facilitate quick
and easy drainage (Figure 8-2). For each final rinse, Type I or Type II water is used
in a pipette container used exclusively for rinses only, with no detergents added
to contaminate the surface of the washer. Some types of plastics have a nonwettable
surface and are therefore more easily cleaned. Some organic solvents,
stiff wash brushes, and abrasive cleaners should not be used on plastics. Plastics
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