clinical applications and maintenance proceedures for laboratory equipment

CLINICAL APPLICATIONS AND MAINTENANCE PROCEEDURES FOR

LABORATORY EQUIPMENT

Without reference, identify at least four out of six basic facts about the clinical applications of a centrifuge.

LABORATORY CENTRIFUGE

Purpose Machine used to separate substances of different

densities that are suspended in a fluid 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: Separating red blood cells from whole blood Separating plasma from whole blood Separating platelets from plasma Separating sediment from urine


Centrifuge components: An electric motor to produce rotation An apparatus called a rotor (or head) to hold the

samples 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

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

Some units (primarily small units) have a set speed (cannot be changed)

Many units have variable speeds

Nearly all units have variable timers


Safety features (should be mandatory on all units purchased) 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 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:


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 x 10-5) x RPM² x r• 1.119 x 10-5 is a conversion factor• r = radius of the rotor in centimeter


Basic factors that a laboratory technician considers when spinning a sample

Speed of rotation 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)• 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• 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 Common laboratory centrifuges

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: Floor standing (larger, hold more/bigger samples) Tabletop (smaller units)


Microhematocrit centrifuges 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 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 Aside from the necessary preventive maintenance

checks, routine verification of RPM and time are mandatory

RPM is normally determined using• Handheld photo-tachometer• Strobe light• Vibrating reed tachometer

Motor brushes (on units that utilize them) should be checked at regular intervals


Without reference, answer questions with at least a 70% accuracy about the laboratory refrigerator.

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 thenext few slides


There are four main components to a refrigeration system 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 auto-refrigeration. 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 Temperature check• 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.


Without reference, answer questions with at least a 70% accuracy about the laboratory microscope.

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. 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. 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 belowthe stage with the diaphragm between them to control the amount and intensity of the light that reachesthe specimen.


Common Maintenance The most common thing that will need to be done

with a microscope is the replacement of the light source bulb.• 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.


• Coarse and fine adjustment mechanismso 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.


o 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.


LABORATORY MICROSCOPE This is not the way to fix a microscope!

clinical applications and maintenance proceedures for laboratory equipment

Documents

force of gravity

centrifuge displaysome

relative centrifugal

centrifuge display rcf

vertical rotor samples

small units

tubeslaboratory centrifuge

basic rotor designs