Page 97 - The Veterinary Laboratory and Field Manual 3rd Edition

66 Willy Schauwers

General purpose centrifuge them in the centrifuge diametrically opposite
to each other or balance them.
The general purpose centrifuge is used:
• Check that the centrifuge is on a firm, level
base and is steady.
• to centrifuge cells, bacteria and parasites
• to separate the serum/plasma or to wash red • Ensure that tubes containing potentially
blood cells pathogenic material are sealed before cen-
• to concentrate parasites in a suspension. trifugation to avoid aerosol forming and
spreading.
A general purpose centrifuge is used with two • Increase the speed of the centrifuge gradually
types of head: the ‘fixed angle’ head and the (if mentioned in the instruction manual).
‘swing out’ head. The ‘swing out’ head is the • Wipe the inside of the centrifuge regularly
one mostly used in the laboratory. (for example, at least weekly) with disinfec-
Several types of tube holders are available: tant (70% ethanol).
• If a breakage occurs:
• buckets to hold one round-bottomed tube
• buckets to hold more than one round- • switch off the centrifuge
bottomed tube • wait for minimum 30 min to allow the
• buckets which can be covered by a lid (screw aerosol to settle
cap). • remove all debris (wear protective gloves)
• disinfect the inside of the centrifuge and
the buckets (use 70% ethanol).
Care, maintenance and general
operating rules
• Fill the tubes no more than three-quarters pH meters
full to prevent spillage.
• Check that the tubes are not too large for the It is critical to know the exact degree of acidity or
centrifuge. Overlong tubes will break during alkalinity (pH) of reagents in many procedures
centrifugation. carried out in a veterinary laboratory, for exam-
• Do not use thin-walled glass tubes, they will ple, the preparation of media for microbiology
break easily during centrifugation. and for solutions used in serology and biochem-
• Close the centrifuge lid before use. istry. If the pH is not correct the culture or test
• Nowadays centrifuges with brushless drive often will be unsuccessful or invalid.
induction motors are available (no need to
replace carbon brushes). The principle of pH
• If required, keep spare carbon brushes in
stock when the centrifuge has a brushed drive pH is a unit of measurement that defines the
motor. If it is difficult to change the brushes, degree of acidity or alkalinity of a solution. It
request help from a qualified electrician. is measured on a scale of 0 to 14. The pH value
• Check that cushions are in the buckets to is essentially a measure of the hydrogen ion
reduce the risk of breakages. concentration.
• Before spinning tubes, ensure that the sam- The internationally accepted symbol, pH,
ples are balanced. To do this balance them on is derived from ‘p’, the mathematical symbol
a two-pan balance (by adding water to the of the negative logarithm and ‘H’, the chemi-
bucket containing the lighter tube) then place cal symbol for hydrogen. The pH value is the

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