CLINICAL APPLICATIONS AND MAINTENANCE PROCEEDURES
FOR LABORATORY EQUIPMENT
LABORATORY CENTRIFUGE
 Without reference, identify at least four out of six basic facts about the clinical
applications of a centrifuge.
 Purpose
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Machine used to separate substances of different densities that are suspended in a
fluid
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Centrifuging only speeds up what will eventually happen with the force of gravity
You are, therefore, creating “artificial gravity”
Works because heavier particles move farther from the center of rotation and collect
at the bottom of the container
Some common applications:
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Separating red blood cells from whole blood
Separating plasma from whole blood
Separating platelets from plasma
Separating sediment from urine
 Centrifuge components:
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An electric motor to produce rotation
An apparatus called a rotor (or head) to hold the samples
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Come in many different sizes depending upon the centrifuge and application
Hold varying amounts and/or sizes of sample containers (usually tubes)
Two basic rotor designs:
 Fixed position (called fixed angle or vertical rotor) – samples remain in an
upright, vertical position during rotation
 Swing-bucket rotors – tube holders are moveable and swing into a horizontal
position during rotation
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Rotors must always be balanced for proper and safe rotation (the higher the rotation
speed the more exact the balance must be)
 Controls for speed and time
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Some units (primarily small units) have a set speed (cannot be changed)
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Many units have variable speeds
Nearly all units have variable timers
 Safety features (should be mandatory on all units purchased)
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Lid locks to prevent lid from being opened while rotor is spinning
Out-of-balance detector to stop rotation if rotor is not balanced properly
 Optional features such as refrigeration or heating system can be added
 Terms
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Centrifugal force – the force that makes rotating bodies move away from the center of
rotation
Centrifugation – the process by which substances of different densities are separated
from one another by centrifugal force
g-Force (or G’s) – unit of measurement for samples undergoing centrifugation (a force
of 1g is equal to the force of gravity at the earth’s surface)
Relative centrifugal force (RCF) – the force (measured in G’s) that a sample undergoes
and depends upon:
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Speed of rotation (measured in revolutions per minute [RPM])
The rotating radius (the distance measured from the center axis of the rotor to the
extreme tip of the tube
Formula for calculating the RCF using the RPM’s from a centrifuge display
RCF = (1.119 · 10-5) · (RPM)2 · r
1.119 · 10-5 is a conversion factor
r = radius of the rotor in centimeter
 Basic factors that a laboratory technician considers when spinning a sample
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Speed of rotation
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This factor, of course, determines the RCF that the sample undergoes
Usually displayed as RPM on the centrifuge display
Some units can calculate and display the actual RCF
Amount of time the sample should spin (centrifugation time)
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The time of centrifugation includes the time of acceleration, but not deceleration
The higher the force of gravity, the less time it will take for separation to occur
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The time required is therefore inverse to the gravities generated by the centrifuge
Amount of time will also depend upon what is being centrifuged (some materials
take longer to separate than others)
 Types of laboratory centrifuges
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Common laboratory centrifuges
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Operate at speeds of about 3,000 RPM, but can attain speeds as high as 7,000
RPM
Some specialized centrifuges are equipped with heating or refrigeration systems
to provide controlled temperatures
Two common configurations:
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Floor standing (larger, hold more/bigger samples)
Tabletop (smaller units)
 Microhematocrit centrifuges
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Very small units capable of high speeds in the range of 10,000 – 11,000 RPM
Used with tiny capillary tubes that hold a very small whole blood sample
Used for quickly estimating red blood cell counts during patient screening and
blood donation procedures
 Micro centrifuges
 Small, tabletop, high-speed units with maximum speeds around 13,000 – 15,000 RPM
 Used for a wide variety of molecular biology studies and various procedures that
require only a short spin cycle
 Ultracentrifuges
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Large, high-cost, specialized machines
Used mostly in research labs for separation of proteins and nucleic acids
Capable of speeds in the range of 20,000 – 100,000 RPM
All ultracentrifuges have refrigeration systems to compensate for the heat generated
by the high rotation speeds
 General Maintenance
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Aside from the necessary preventive maintenance checks, routine verification of RPM
and time are mandatory
RPM is normally determined using
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Handheld photo-tachometer
Strobe light
Vibrating reed tachometer
Motor brushes (on units that utilize them) should be checked at regular intervals
LABORATORY REFRIGERATOR
 Without reference, answer questions with at least a 70% accuracy about the laboratory
refrigerator.
 Most refrigeration systems are based on a vapor compression cycle for cooling.
 This is a cycle where a refrigerant is forced to change from liquid to vapor and back which
causes a strong cooling reaction.
 This is explained in the
next few slides
 There are four main components to a refrigeration system
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Compressor – Refrigerant enters compressor as a vapor and is compressed to a high
pressure
Condenser – cools the vapor until it starts condensing
Expansion Valve (also called throttle valve) – liquid refrigerant goes through which
causes the pressure to abruptly decrease causing flash evaporation and autorefrigeration. This remaining mixture is part liquid and part vapor at a low
temperature and pressure.
Evaporator – The refrigerant then goes through the evaporator coils or tubes where a
fan circulates air from within the refrigerator across the coils, thus cooling the air in
the refrigerator
 Calibration and Maintenance
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Temperature check
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Use calibrated thermometer to verify temperature is within tolerance
Clean dust and dirt off of any fans as well as off of the evaporator coils or tubes.
 LABORATORY MICROSCOPE
 Without reference, answer questions with at least a 70% accuracy about the laboratory
microscope.
 Definition – A microscope is an instrument used to look at objects to small to see with the
naked unaided eye.
 The most common type of laboratory microscope is an optical microscope. This is usually
in the form of a light microscope.
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A light microscope uses a series of lenses to allow you to view a lighted object with up
to 1500 times magnification.
 There are a few components of note in a light microscope.
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Eyepieces – this is the part that you look directly through. They normally contain a
lens with a small magnification amount – usually around 10 times.
Objectives – these are the main lenses in the microscope and are responsible for the
largest portion of magnification
Stage and stage controls – the stage is the surface on which your specimen is placed.
The stage can be moved a small amount using the stage controls in most microscopes.
The controls are normally separated into coarse and fine adjustments.
Diaphragm and light source – The light source is usually located below
the stage with the
diaphragm between
them to control the
amount and intensity
of the light that reaches
the specimen.
 Common Maintenance
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The most common thing that will need to be done with a microscope is the
replacement of the light source bulb.
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This is a very simple procedure in most units
Other that bulb replacement you may be required to clean the lenses or clean or
repair the coarse and fine adjustment mechanisms. Anything beyond this normally
requires sending the microscope out for service, but luckily problems of this nature
are extremely rare.
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Coarse and fine adjustment mechanisms
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The coarse and fine adjustment mechanisms are based on a series of gears
attached to two different adjustment knobs. As each of these knobs are
turned the stage is moved. The coarse adjustment causes the stage to move
quickly while the fine adjustment moves it slowly. This causes the specimen
to move which helps to focus the image.
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There is one thing to keep in mind about the maintenance of the coarse and
fine adjustment mechanisms.
 From time to time the gears that control these adjustments will become
dirty or clogged with dirt and/or other debris.
 You should know when this is the case because you will have difficulty
adjusting the microscope.
 Stage either won’t move at all or will move with short jerky motions.
 In this situation you must disassemble and clean the adjustment
mechanisms. When you do this you must be extremely careful to
keep track of all of the small pieces within the microscope. Nothing is
worse than going through all of the work to fix something and then it
won’t work because you lost a piece.
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This is not the way to fix a microscope!