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Dr. Tarek El Sewedy. Pharos university Faculty of Allied Medical SCIENCE Clinical Laboratory Instrumentation (MELI-201). Clinical Laboratory classification Balances and Centrifuges. Lecture 2. Intended Learning Outcomes. By the end of this lecture the student would learn the following:
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Dr. Tarek El Sewedy Pharos universityFaculty of Allied Medical SCIENCEClinical Laboratory Instrumentation(MELI-201)
Clinical Laboratory classification Balances and Centrifuges Lecture 2
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
Classification of clinical laboratories • The world Health Organization (WHO) lists four kinds of levels of laboratories based on their biosafety. • Basic laboratory level I • Basic laboratory level II • Containment laboratory (Level III) • 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 workerand 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. • Suchorganisms 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 personneland 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 personto another. These laboratories are usually a separate building with strictly controlled access.
Balances • Balances in medical laboratory may be: A. Rough balances (mechanical balances) B. Analyticalbalances • 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 electricityor battery These balances are used: 1. To weigh small quantities usually in milligram(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 • 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 heavier lighter 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.
Centrifugal force increases with the speedof 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.
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
Decant supernatant 1000g/10 min 3000g/10 min etc. Differential centrifugation of a tissue homogenate
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 ultracentrifugescan 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.
CsClGradient UltracentrifugationSeparation According to density
Hand centrifuges: • Operated by handand they are most commonly used in small laboratory for routine purposes, Used for preparation of urinarysediments 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 • Read the manufacturer’s instructions. • Placing a centrifuge on a firm level bench • Whenever possible using plastic tubes made from polystyrene or autoclavable. • Always balancing the tubes that are being centrifuged. • Never open the centrifuge while it is still spinning. Never try to slow it down with your hand. • Most centrifuges have a brake, use it only when appropriate
Assignment • AssemTalal: 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
