General Laboratory Instruments and Equipments

• LABORATORY GLASSWARES AND PLASTICWARES
• Cleaning of Laboratory Glassware and Plastic ware 

 EQUIPMENT'S FOR WEIGHING

1. Analytical balance
2. Electronic balance

3. Direct read-out and top-loading balance.
1. Analytical balance
2. Electronic balance
3. Direct read-out and top-loading balance.

• AUTOCLAVE
• INCUBATOR
• WATER BATH

Use and Care of Water Bath
Distillation
1. Splash guard
2. Cut out devices
3. Easy cleaning

Deionization

• Different models of deionize

REFRIGERATORS AND FREEZERS 

pH meter - click here

• Principle,

• Components of pH meter,

• Measurement of pH 

• using pH meter

General Laboratory Instruments and Equipments:- 

Instruments and equipments are essential for the functioning of any medical laboratory. The last twenty years have witnessed great progress in the area of automation in the field of medical laboratory technology.

 It has been observed that this development has led to a more efficient medical laboratory practice, and in the long run, less expensive service. The manufacturers of laboratory instruments are continually introducing new lines of products into the market. 

Most of these new instruments are computerized. It has thus become necessary for members of the laboratory staff to acquire at least a basic knowledge of computer operation.

In addition to the essential general instruments and equipments, there are those which are of specific importance to, and used in particular departments. Some of the essential instruments and equipments are discussed below.

LABORATORY GLASSWARES AND PLASTICWARES:- 

Most of the routine laboratory wares used to be of glass, but recent advances made in the use of plastic resins to manufacture a wide range of plasticwares have led to a gradual replacement of glasswares with durable plasticwares. 
 

The plastic ware used in the laboratory should be of high quality. The plasticwares are also cheaper and safer to use than glassware. 

The glasswares have the minor advantages of being re-usable and autoclavable. However, it is heavier, more costly and easily broken. In fact, in this age of good awareness of the dangers posed by hepatitis and Human Immunodeficiency Viruses (HIV), most laboratories are encouraged to make use of plasticwares. 

Furthermore, most of the plasticwares are disposable, thereby cutting down on the cost of cleaning. The plasticwares are fashioned and shaped exactly like the glasswares.

A range of laboratory glasswares and plasticwares used in a medical laboratory is shown in Figs respectively.

Cleaning of Laboratory Glassware and Plastic ware:

- The use of clean, unbroken glassware is one of the many factors that ensure accurate results in the laboratory investigations. Different methods of cleaning glassware are available depending on the glassware used. In addition to being physically clean, laboratory wares for clinical chemistry must be chemically clean, and those for bacteriology must be bacteriologically clean, or sterile.

All laboratory glassware can withstand strong disinfectants and chemicals. It is important never to allow dirty glassware to dry-out. This is because once dried out on the surface, it is not easy to remove the dirt. It is essential therfore, to have a soaking jar available in the working area.

A new glassware is often slightly alkaline and so, should be soaked for several hours in dilute (approx. 1 %) hydrochloric acid or nitric acid solution. This glassware is then washed and rinsed thoroughly in distilled water.

It is important that contaminated glassware, as that used with patients' specimens, should be decontaminated before it is washed. This is carried out by presoaking in 5 % hypochlorite solution or by boiling, autoclaving, or some other similar procedure. The cleaning job of the contaminated glass ware is made much easier if the soaking was carried out in a solution of detergent.

The plastic wares are given the same treatment as the glassware except that they are soaked in very dilute disinfectants, and some of them are non-autoclavable.

EQUIPMENT'S FOR WEIGHING:- 

 Weighing equipments are essential in a medical laboratory. They are used to weigh substances for the preparation of reagents. Weighing balances, have different sensitivity ranges depending on the nature and amount of the substance to be weighed.

There are three types of balances which are very useful in the laboratory. They are:

1. Analytical balance

2. Electronic balance

3. Direct read-out and top-loading balance.

 FOR MORE ABOUT  EQUIPMENT'S FOR WEIGHING CLICK HERE

AUTOCLAVE:

- This is a valuable piece of equipment for sterilising articles and media by steam under pressure. The principle and use of the autoclave is discussed in the chapter on sterilisation in Bacteriology.                           (FOR  MORE CLICK HERE)

INCUBATOR:

-The incubator is required for incubation, under controlled temperature, of microbiological cultures and many other laboratory tests. Electric models are mostly in use, though there are a few models that are battery operated.

The incubators are fitted with thermostats. The operating temperature range is 5°C to 80°C. For alarge capacity incubator, air is circulated by means of a fan while air circulation in the small capacity incubator is by natural convection. For use, maintenance and care, the manufacturer's instructions should be followed carefully.

WATER BATH:

- The water bath, like the incubator, is required for controlled temperature incubation of cultures and liquids, and many other laboratory tests. The temperature of the water bath is thermostatically controlled and can be set at any desired level ranging usually from 20°C to 100°C. 

The water baths are available in various types and capacities. The heating coil may be of immersion type or enclosed in a case. Some models have propellars to help to circulate water so that identical temperature is maintained throughout the water bath.

Use and Care of Water Bath:-

1. Maintain the minimum level in the water bath with chemically pure water. Avoid use of tap water as salts from tap water may get deposited on the coil and so affect its function.

2. Always use a thermometer to check that the temperature is stable at the desired level.

3. Make sure that the substance being incubated is below the surface of water in

the bath.

4. It is advisable to cover the tubes, flasks or plates during incubation to avoid contamination and dilution as a result of condensation of water from the lid of the water bath.

 5. Clean the water bath regularly.

WATER DISTILLER AND DEIONIZER

Chemically pure water is required for the performance of many laboratory tests, especially in clinical chemistry. Sources of pure water are by distillation and by deionization.

Distillation 

-This is a process of boiling water and then condensing the resulting steam on a cold surface, the condenser, to yield pure water. The instrument used for distillation is called a still. The tap water is introduced into the still. It is electrically heated by a heating coil. On boiling, the steam produced is condensed in the condenser and cooled by circulating tap water.

The cooled steam is collected as distilled water. The quality of pure distilled water should be such that it must be free from dissolved salts, and should be clear, colorless, odourless and tasteless. It can also be made pyrogen free if it contains only condensed steam and is collected in a clean, sterile container. Pyrogen is defined as a substance, usually of bacterial origin which is capable of causing fever if transfused in an intravenous fluid.

Water stills Most water stills are electrically heated and they all contain the following special features:

1. Splash guard: This device prevents untreated water from splashing over into the distillate.

2. Cut out devices:These devices switch offthe power in emergencies such as power failure, and reduction of water supply. Some models are also provided with the cut-out device that switches off the power when the collecting container is full. These devices provide safety as the stills can be

operated without continuous attention. 

3. Easy cleaning: The water still should beregularly cleaned bacause of deposition of salts on the boiler. For this reason it should be so constructed that it can be easily dismantled and should also be fixed in an easily accessible position.

The rate of production of distilled water depends on the power of the elements of the still. An average sized still produces about 4 to 5 litres of distilled water per hour.

Figures (a) and (b) show the working of stainless steel and glass stills.

Testing distilled water A number of simple chemical tests are employed for testing the quality of distilled water. These tests include: 

(a) Test for chlorides: Add a few drops of 10 % silver nitrate to a small quantity of water under test. Good distilled water should show no cloudiness.

 (b) Test for sulphates: Add a few drops of 10% barium chloride to a small volume of water under test. Absence of precipitate indicates distilled water free of sulphates.

Deionization: -  
De ionization is another method of obtaining chemically pure water. The method involves passing tap water through anion and cation exchange resins. 

Cations such as calcium, magnesium and sodium are exchanged (removed) by the resin and replaced by hydrogen ions. Anions such as sulphates, chlorides, bicarbonates, silica and nitrates are similarly exchanged by the anion resins and replaced by hydroxyl ions.

The hydrogen ions combine with the hydroxyl ions to form water. Deionised water has a low electrical conductivity and is free from water soluble salts, but is not pyrogen free. It must not, therefore, be used to prepare intravenous solutions.

There are different models of deionizer-

The portable hand-held deionizer, the bench models or the wall-mounted deionisers. Figure 3.9 shows a wall-mounted deionizer. The newest models available in the market are easy to operate. 

The initial installation, however, should be done by a knowledgeable technician and enough spare parts for the instrument should be readily available.

The resins should be regenerated after a period of usage. The procedure for regeneration is to pass hydrochloric acid through the cation resin, and sodium hydroxide through the anion resin, and then rinsing thoroughly with distilled water. 

Some manufacturers actually opt to carry out this procedure for their customers.

For some specialized laboratory tests, for example, enzyme estimations, water of high degree of purity is required. This type of water is easily obtained by passing distilled water through a deionization column or by double distillation of water. 

The use of deionization column is more convenient in practice than the process of double distillation, and has the added advantage that the resins need less frequent regeneration than when they are used with tap water.

Testing demonized water Demonized water has high resistance to electricity, and measuring this resistance is an easy way of determining the quality of water produced.

A conductivity meter is usually a part of the deionizer. Generally, a resistance of greater than about 1.5 to 2.0 milli Ohms per ml is acceptable for most laboratory usage.

REFRIGERATORS AND FREEZERS

Some reagents and chemicals are best kept at a temperature of 4°C, plus or minus 2°C. In microbiology laboratory, culture media and bacterial cultures are refrigerated to prevent contamination and preserve the cultures. The blood bank is a specially built refrigerator.

The size of the refrigerator meant for a laboratory depends on the envisaged usage. In big and busy laboratories, the refrigerator is usually replaced by a well-insulated "cold room".Some samples and reagents are best kept frozen. This ensures that the antigenic properties of the samples and the potency of the reagents are retained.

For short term storage, the common domestic freezer of about -20°C temperature is quite adequate. But for a long time storage, deep freezers of about - 80°C are recommended.

Refrigerators and freezers are durable equipments that can last for years if properly used and maintained. It is important to avoid overloading of the refrigerator or the freezer.