EXERCISE – 1
COMMON LABORATORY EQUIPMENTS AND THEIR USE IN
MICROBIOLOGY LABORATORY
INTRODUCTION:
Any individual working in laboratory must learn the use and care of laboratory
Instruments. Most instruments, for their efficient use, require some measure of
training and skill. Instruments are delicate and should be handled carefully. Hence it
is advisable to read the ‘instruction manual’ carefully before its operation or should
contact the person who is familiar to the instrument. It provides information regarding
operation, maintenance, trouble shooting and essential knowledge for repair jobs.
In microbiology laboratory, following instruments are used:
1. Weighing Balance 7. Water Bath
2. pH Meter 8. Orbital Shaker
3. Autoclave/ Steam Sterilizer 9. Colony Counter
4. Hot Air Oven 10. Centrifuge
5. Laminar Air Flow Cabinet 11. Refrigerator
6. Incubator
1. WEIGHING BALANCE:
Several types of balances such as single pan
balance, top pan balance, analytical balance are
available for weighing different ingredients required
during course of experimentation. Accuracy of weighing
is determined by sensitivity of the balance, which may
be as low as 0.0001 gram (1 milligram). Electronic
balances are easy to handle and are more accurate and
sensitive.
1. Electronic balances are highly sensitive and even a
little movement of air may affect the accuracy of the
measurements.
2. After every use clean the pan with dry clean tissue
paper and keep in dust proof chamber.
2. pH METER:
As a convenient way of expressing hydrogen ion concentration, S.P.L.
Sorensen introduced the symbol pH in 1909. ‘pH is defined as the negative value
of the logarithm to the base 10 of the hydrogen ion concentration or the
logarithm (to the base) of the reciprocal of the hydrogen–ion concentration’.
pH = –log 10 [H+] = log 10/[8+] , or [H+] =10 –pH
The most reliable way to measure the pH of a solution is to use pH meter. A
pH meter measures the differences in potential between two solutions of different pH
value.
2
PRINCIPLE:
When two solutions containing
hydrogen ion are separated by the bulb of a
glass pH electrode that is hydrogen sensitive,
an electrical potential is developed across the
thin glass separating the two solutions. If the
solution inside the bulb is of fixed hydrogen
ion concentration, the potential across the
glass will change as the hydrogen ion
concentration of the other solution varies.
This difference in potential can be measured
by making an electrical connection between
the internal element of the glass electrode
and a reference electrode (potential of which is known). pH meter should be
calibrated using standard solutions of pH 4.0, 7.0 and 9.0.
3. AUTOCLAVE/ STEAM STERILIZER:
Autoclave was developed by Charles Chamberland in 1879, which
tremendously promoted growth of microbiology discipline.
PRINCIPLE:
Increase in pressure of steam is directly proportional to the increase in
temperature. In other words, it is called as ‘Steam under Pressure’. Moist heat has
more penetration power, kills living cells by degrading nucleic acid or by denaturing
enzymes and other essential proteins. It may also disrupt cell membrane. Autoclave
is used for sterilization of various utilities specially the media under saturated steam
pressure at any selected point between 10–20 Pounds per square inch (psi).
Autoclaves may be either vertical or horizontal. It is a double or triple walled
unit mounted on a sturdy metal (Steel) body. The heating element is fitted at the
base of the cylinder. The space between the outer and steam jacket is insulated to
minimize temperature loss. The lid is fitted with rubber gasket and tightened by wing
nut/radial locking system. All autoclaves are fitted with standard accessories such as
water indicator, pressure gauge, temperature gauge, steam release valve, safety
valve etc. Generally sterilization is carried out at 15 psi for 20 minute and time here
is considered after the pressure is achieved.
Relationship between pressure and temperature is as follows.
Pressure Saturated steam*
[OC]
Pressure (psi) Saturated steam*
[OC]
05 109 20 126
10 115 25 130
15 121 30 135
(*Pressure–temperature relationship holds true only if the chamber is completely
filled with saturated steam only.)
PRINCIPLE:
When two solutions containing
hydrogen ion are separated by the bulb of a
glass pH electrode that is hydrogen sensitive,
an electrical potential is developed across the
thin glass separating the two solutions. If the
solution inside the bulb is of fixed hydrogen
ion concentration, the potential across the
glass will change as the hydrogen ion
concentration of the other solution varies.
This difference in potential can be measured
by making an electrical connection between
the internal element of the glass electrode
and a reference electrode (potential of which is known). pH meter should be
calibrated using standard solutions of pH 4.0, 7.0 and 9.0.
3. AUTOCLAVE/ STEAM STERILIZER:
Autoclave was developed by Charles Chamberland in 1879, which
tremendously promoted growth of microbiology discipline.
PRINCIPLE:
Increase in pressure of steam is directly proportional to the increase in
temperature. In other words, it is called as ‘Steam under Pressure’. Moist heat has
more penetration power, kills living cells by degrading nucleic acid or by denaturing
enzymes and other essential proteins. It may also disrupt cell membrane. Autoclave
is used for sterilization of various utilities specially the media under saturated steam
pressure at any selected point between 10–20 Pounds per square inch (psi).
Autoclaves may be either vertical or horizontal. It is a double or triple walled
unit mounted on a sturdy metal (Steel) body. The heating element is fitted at the
base of the cylinder. The space between the outer and steam jacket is insulated to
minimize temperature loss. The lid is fitted with rubber gasket and tightened by wing
nut/radial locking system. All autoclaves are fitted with standard accessories such as
water indicator, pressure gauge, temperature gauge, steam release valve, safety
valve etc. Generally sterilization is carried out at 15 psi for 20 minute and time here
is considered after the pressure is achieved.
Relationship between pressure and temperature is as follows.
Pressure Saturated steam*
[OC]
Pressure (psi) Saturated steam*
[OC]
05 109 20 126
10 115 25 130
15 121 30 135
(*Pressure–temperature relationship holds true only if the chamber is completely
filled with saturated steam only.)