PHAROS UNIVERSITY

FACULTY OF ALLIED MEDICAL SCIENCE

CLINICAL LABORATORY

INSTRUMENTATION

(MELI-201)

Dr. Tarek El Sewedy

LECTURE 2

Clinical Laboratory classification

Balances and Centrifuges

Intended Learning Outcomes

By the end of this lecture the student would learn the following:

1. Laboratory classification.

2. Balances.

3. Centrifuges

Lecture content

1. Laboratory classification.

2. Balances.

3. Centrifuges

EARLY LABORATORY INSTRUMENTATION

EARLY LABORATORY INSTRUMENTATION

EARLY LABORATORY INSTRUMENTATION

EARLY LABORATORY INSTRUMENTATION

Classification of clinical laboratories

The world Health Organization (WHO) lists four

kinds of levels of laboratories based on their

biosafety.

1. Basic laboratory level I

2. Basic laboratory level II

3. Containment laboratory (Level III)

4. Maximum containment laboratory

Basic laboratory level I

Basic laboratory level I is the simplest kind and adequate for

work with organisms which have low risk to the individual

laboratory personnel as well as to the members of the

community.

Such organisms are categorized under Risk Group I by WHO.

These organisms are unlikely to cause human diseases.

Example, food spoilage bacteria, yeasts.

Basic laboratory level II

Basic laboratory level II is suitable for work with organisms that

predispose to moderate risk to the laboratory worker and a limited

risk to the members of the community.

Such organisms are categorized under Risk Group II by WHO.

They can cause serious human diseases but not serious hazards due

to the availability of effective preventive measures and treatment.

Example, staphylococci and streptococci.

Such laboratory should be clean, provide enough space, have

adequate sanitary facilities and equipped with autoclave.

Level III Containment laboratory

Containment laboratory is more advanced and it is used for work

with infectious organisms that present a high risk to the laboratory

personnel but a lower risk to the community.

Such organisms are categorized under Risk Group III by WHO.

Example, Salmonella and HIV.

The principle is to isolate those organisms from the basic laboratory

and limit the activities which are particularly hazardous. They are

easily transmitted through airborne, ingestion of contaminated food

or water.

Such laboratory should be a separate room with controlled access

and clothing by authorized staff. It should also be fitted with

microbial safety cabinet.

Maximum containment laboratory

Maximum containment laboratory is intended for work with

viruses, which predispose to a high risk for both laboratory

personnel and the community.

Such organisms are categorized under Risk Group IV by WHO.

Example, Small pox, Ebola and others.

Most of these organisms cause serious disease and readily

transmitted from on person to another. These laboratories are

usually a separate building with strictly controlled access.

Respect Lab Containment rules for your safety

Balances

Balances

Balances in medical laboratory may be:

A. Rough balances (mechanical

balances)

B. Analytical balances

should be kept clean and located in an area

away from heavy traffic, large pieces of

electrical equipment, and open windows.

To minimize any vibration, as interference

that may happen, a slab of marble is

placed under the balance.

Rough balances

• Used for weighing substances, which do not call for extreme

accuracy.

• They do not require electricity or battery power.

used to:

• To weigh large amounts (up to several kilo grams)

• When a high degree of accuracy is not required.

Analytical balances

Highly sensitive instrument.

requires electricity or battery

These balances are used:

1. To weigh small quantities usually in milli gram(mg)

range.

2. When great accuracy is required.

Use and care of balances

Read carefully the manufacturer’s instructions.

Position the balance on a firm bench away from vibration.

Before starting to weigh, zero the balance as directed by

the manufacturer.

Never put the chemicals directly on the balance pan.

Use small brush to remove any chemical, which may have

been spilt on the balance.

Container of silica should be kept inside the balance case to

remove any moisture present in the atmosphere.

Keep the balance clean, being particularly careful not to let dirt

accumulate near the pivots and bearings.

Centrifuges

Centrifuges

Is an equipment that is used to separate solid matter from a liquid

suspension by means of centrifugal force.

They sediment particles (cells, bacteria, parasites, etc.) suspended in fluid

The suspended materials are deposited in the order of their weight.

Different materials need a different rate of spinning to obtain adequate

separation. So, all centrifuges can be adjusted to control the rate

at which the sample spins.

Spinning can be measured as revolutions per minute (rpm)

Basic principle of operation

When a body is rotated in circular movement at

speed, centrifugal force is created that drives the

body away from the center of the circular movement.

The greater the outward pull due to rotation

“centrifugal force”, the more rapid and effective is

the sedimentation. As a result, elements are

thrown to the bottom of the tube followed by

particles.

heavier

lighter

Centrifugal force increases with the speed

of rotation that is the revolution of the

rotor per minute (rpm) and the radius of

rotation.

The actual sedimentation achieved at a

given speed depends therefore, on the

radius of the centrifuge.

Classes of centrifuges and their applications

Differential centrifugation.

Separation is achieved primarily based on the size and weight of the

particles in differential centrifugation. This type of separation is

commonly used in simple pelleting and in obtaining partially-pure

preparation of subcellular organelles and macromolecules.

For the study of subcellular organelles, tissue or cells are first disrupted to

release their internal contents. This crude disrupted cell mixture is

referred to as a homogenate. During centrifugation of a cell homogenate,

bigger and heavier particles sediment than lighter ones and this

provides the basis for obtaining crude organelle fractions by differential

centrifugation.

FASTER

Differential centrifugation of a tissue homogenate

1000g/10 min

Decant supernatant

3000g/10 minetc.

Basic components of centrifuges

1. Shaft: - It is the central part that rotates when

spinning is effected.

2. Rotor: - It is a part that holds the bucket

3. Bucket: - Are portions that hold test tubes

containing a given sample.

Special centrifuges called ultracentrifuges can exceed

100,000 rpm.

The forces in a sample spinning at 10,000 rpm can

exceed 17,000 g-force units. This is the equivalent of a

150-pound person being pressed upon by a 1,275- kg

weight.

Ultracentrifuges can exceed 1 million g-force units.

Respect the Ultra

CsCl Gradient UltracentrifugationSeparation According to density

Cont , gradient centrifugation

Hand centrifuges:

Operated by hand and they are most commonly used

in small laboratory for routine purposes, Used for

preparation of urinary sediments and to concentrate

parasites from the given specimen.

Rotors Based on their tube angle rotation, there are two types.

A. Swing head: -

The head is designed to swing the tubes to the

horizontal position during centrifugation process.

B. Fixed head: -

They are fixed and have different angles.

Use and care of centrifuges

1. Read the manufacturer’s instructions.

2. Placing a centrifuge on a firm level bench

3. Whenever possible using plastic tubes made from

polystyrene or autoclavable.

4. Always balancing the tubes that are being centrifuged.

5. Never open the centrifuge while it is still spinning. Never try

to slow it down with your hand.

6. Most centrifuges have a brake, use it only when appropriate

Assignment

Assem Talal: is selected to make the

assignment on different types of

centrifugation.

Suggesting reading

Encyclopedia of Medical Devices and Instrumentation, 2nd ed. New York: Wiley, 2006