Archive for May, 2014


May 30th, 2014

Pressure is defined as the force exerted over a unit area. Force may be exerted by liquids, gases, and solids. Pressure is governed by the following equation:

P = F/A


P = Pressure , F= force and A = area

Measurement of Pressure

The pressure of a fluid is measured by following devices:

  1. Manometers
  2. Mechanical gauges


A manometer is a device for measuring fluid pressure consisting of a bent tube containing one or more liquids of different densities.A known pressure (which may be atmospheric) is applied to one end of the manometer tube and the unknown pressure (to be determined) is applied to the other end.

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Manometer operates on hydrostatic balance principle. A basic manometer includes a reservoir,filled with a liquid. The reservoir is usually enclosed with a connection point that can be attached to a source in order to measure its pressure. A transparent tube, or column, is attached to the reservoir. The top of the column may be open, exposing it to atmospheric pressure. Or, the column may be sealed and evacuated. Manometers that have open columns are usually used to measure gage pressure, or pressure in reference to atmospheric pressure. Manometers with sealed columns are used to measure absolute pressure, or pressure in reference to absolute zero. Manometers with sealed columns are also used to measure vacuum.

When a manometer is connected to a process, the liquid in the column will rise or fall according to the pressure of the source it is measuring. In order to determine the amount of pressure, it is necessary to know the type of liquid in the column, and the height of the liquid. The type of liquid in the column of a manometer will affect how much it rises or falls in response to pressure, its specific gravity must be known in order to accurately measure pressure.

Manometers are accurate, they are often used as calibration standards. The shape of the liquid at the interface between the liquid and air in the column affects the accuracy of the manometer. This level is called the meniscus. The shape of the meniscus is determined by the type of liquid used. In order to minimize the errors that result from the shape of the meniscus, the reading must be taken at the surface of the liquid in the center of the column.

The quality of the fill liquid will also affect the accuracy of pressure measurements. The fill liquid must be clean and have a known specific gravity.

Classification of Manometer

Broadly manometers are classified into two classes

  1. Simple manometers ; simple manometers are those which measure pressure at a point in a fluid containing in the pipe or a vessel.

Simple manometer is of many types

  • Piezometer
  • U- tube manometer
  • Single column manometer
  1. Differential manometers ; Differential manometers measure the difference of pressure between any two points in a fluid contained in a pipe or vessel. Differential manometer is of following types
  • U-tube differential manometer
  • Inverted U- tube differential manometer ; This type of manometer is used for measuring the difference of two pressures (where accuracy is the major consideration)

Piezometer is one of the simplest forms of manometers. It can be used for measuring moderate pressures of liquids. The setup of piezometer consists of a glass tube, inserted in the wall of a vessel or of a pipe. The tube extends vertically upward to such a height that liquid can freely rise in it without overflowing. The pressure at any point in the liquid is indicated by the height of the liquid in the tube above that point.

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Pressure at point A can be computed by measuring the height to which the liquid rises in the glass tube. The pressure at point A is given by p = wh, where w is the specific weight of the liquid

Limitations of Piezometer

  • Piezometers can measure gauge pressures only. It is not suitable for measuring negative pressures.
  • Piezometers cannot be employed when large pressures in the lighter liquids are to be measured since this would require very long tubes, which cannot be handled conveniently.
  • Gas pressures cannot be measured with piezometers, because a gas forms

U – tube manometer

The piezometer cannot be employed when large pressures in the lighter liquids  are to be measured, since this would require very long tubes , which cannot be handled conveniently.Further more, gas pressures cannot be measured by the piezometers because a gas forms no free atmospheric surface. These limitations can be overcome by the use of U-tube manometers. A U-tube manometer consists of a glass tube bent in U-shape, one end of which is connected to a point at which pressure is to be measured and other end remains open to the atmosphere .Using a “U’ Tube enables the pressure of both liquids and gases to be measured with the same instrument. The “U” is filled with a fluid called the manometric fluid. The fluid whose pressure is being measured should have a mass density less than that of the manometric fluid

Characteristics of liquid used in U-tube Manometer:

  • Viscosity should be low.
  • Low surface tension is required.
  • The liquid should stick on the walls.
  • Should not get vaporized.
  • The two fluids should not be able to mix readily that is, they must be immiscible.

Advantages of U-tube Manometer:

  • Simple in construction
  • Low cost hence easy to buy.
  • Very accurate and sensitive
  • It can be used to measure other process variables.


  • Fragile in construction.
  • Very sensitive to temperature changes

Applications of U-tube manometer:

  • It is used for low range pressure measurements.
  • Extensively used in laboratories.
  • Is used in Orifice meter and Venturi meter for flow measurements.
  • It is used for calibration of gauges and other instruments.
  • It is used for measuring pressure drop in different joints and valves.

Single column manometer (micromanometer)

The U-tube manometer described above usually requires the reading of fluid levels at two ormore points since a change in pressure causes a rise of the liquid in one limb of the manometer and adrop in the other. This difficulty is however overcome by using single column manometers. A singlecolumn manometer is a modified form of a U-tube manometer in which a shallow reservoir having alarge cross-sectional area (about 100 times) as compared to the area of the tube is connected to one limb of the manometer,

Factors affecting manometer

Basic manometer principle of hydrostatic balance is inherently 100% accurate but there are some factors that can affect the pressure measurement

  • Characteristics of indicating fluid ; Fluid must have good ‘Wetting’ characteristics and should be capable of forming a consistent well shaped meniscus in the indicating tube to facilitate accurate and repeatable reading.
  • Readability; Scales must be clear, sharp, accurate and easy to read.

Advantages of Manometers

  • Easy to fabricate and relatively inexpensive;
  • Good accuracy;
  • High sensitivity;
  • Require little maintenance;
  • Not affected by vibrations;
  • Specially suitable for low pressure and low differential pressures; and
  • It is easy to change the sensitivity by affecting a change in the quantity of manometric liquid in the manometer

Limitations of manometer

  • Usually bulky and large in size.
  • Being fragile, get broken easily.
  • Readings of the manometers are affected by changes in temperature, altitude and gravity.
  • A capillary effect is created due to surface tension of manometric fluid, and
  • For better accuracy meniscus has to be measured by accurate means.


  • specific pressure monitoring applications
  • Visual monitoring of air and gas pressure for compressors.
  • Vacuum equipment and specialty tank applications such as medical gas cylinders, fire extinguishers.
  • In power plants,mercury absolute manometer have been used to check condenser efficiency by monitoring vacuum at several points of the condenser
  • Used for the research of atmosphere of other planets.
  • And many more applications such as in whether studies, research labs, gas analysis and in medical equipments.
  • Some types of liquids used in manometers are toxic and can be damaging to the environment. Therefore, when using manometers to measure or indicate pressure, do not connect any manometer to a pressure that has the potential to exceed the range of the manometer. This could cause the liquid to be forced out of the tube.
  • In addition, since the tubes in many manometers are made of glass and can be easily broken, it is important to use care in handling these manometers.
  • Never operate damage equipment.
  • Meter and its tubing should be free from any breaking and blockage.
  • Electronic manometers do not measure water pressures; under these conditions they will fail. Do not exceed 10 PSI input pressure.


  • Some types of liquids used in manometers are toxic and can be damaging to the environment. Therefore, when using manometers to measure or indicate pressure, do not connect any manometer to a pressure that has the potential to exceed the range of the manometer. This could cause the liquid to be forced out of the tube.
  • In addition, since the tubes in many manometers are made of glass and can be easily broken, it is important to use care in handling these manometers.
  • Never operate damage equipment.
  • Meter and its tubing should be free from any breaking and blockage.
  • Electronic manometers do not measure water pressures; under these conditions they will fail. Do not exceed 10 PSI input pressure.

Major equipments used in cell culture

May 30th, 2014

What is Tissue/Cell Culture?

Tissue/cell culture is a biological method of asexual propagation where a very small piece of tissue (shoot apex, leaf section, or even an individual cell) is excised (which is known as Explants) and placed in sterile /aseptic culture in a test tube/petri dish/tissue culture container containing a special culture media.

A tissue/cell culture is used for rapid multiplication of an organism. A very specialized laboratory with sterile/aseptic conditions is required for tissue culture. All the procedure involved in tissue culture should be carried out in a aseptic conditions.

Steps involved in Tissue/cell Culture are

Explants ; excision of the plant parts.Place the explants in a tissue culture container/test tubes/petri dishes.
Multiplication ; Tissue grows and produce small plants.(Rapid multiplication by transfer of fresh culture).
Transplanting the plant into some kind of acclimation container.

Major equipments involved in Tissue/cell culture for providing various conditions such as Aseptic conditions


Incubation is a significant process for the growth of cell in the Tissue/Cell Culture. Growing cells require strictly controlled environment. Incubator provides the correct growth conditions, such as temperature, degree of humidity and CO2 levels in a controlled and stable manner. Incubators minimize contamination problems apart from offering energy efficiency and safe environment for cell lines. Some Incubators also have the facility to control oxygen level. Copper-coated incubators are reported to reduce the risk of microbial contamination within the Incubator due to the microbial inhibitory activity of copper. The inclusion of a bactericidal agent in the Incubator water trays will also reduce the risk of bacterial and fungal growth. However, there is no substitute for regular cleaning. CO2 Incubators provide best optimal conditions for Cell/Tissue Culture.


Shakers are one of the important Tissue/Cell Culture equipments. Laboratory shakers including Incubated Shakers are used in a wide variety of scientific applications such as

Molecular biology,
Plant and animal cell culture,
Genetic research,
Drug discovery and


Centrifuges are used routinely in Tissue/Cell Culture as part of the subculture routine for most cell lines and for the preparation of cells for Cryopreservation. Only low speed centrifuges are used generally at 20 degree C to avoid disruption of the separated bands of cells.The motor releases the heat which leads to the increase in temperature. Therefore, use of low temperature for centrifugation is recommended so that cells are not exposed to high temperature. The centrifuge should have a clear lid so that the condition of the load can be observed without opening the lid. This will reduce the risk of the operator being exposed to hazardous material if a centrifuge tube has broken during centrifugation. Care should always be taken not to over-fill the tubes and to balance them carefully. These simple steps will reduce the risk of aerosols being generated.

Laminar Air Flow

Laminar Air Flow provides a work area with aseptic/sterile conditions for the tissue culture. Laminar Air Flow has continuous displacement of air (it provides streamline flow of air) that passes through HEPA (High Efficiency Particulate Air) filter that removes the particulates from the air.
Laminar Air Flow are equipped with a UV lamp that should be turned on about 10-20 minutes  before being used to sterilize the shell or cabinet or the surface of the Laminar Air Flow to avoid any kind of contaminations. Wipe down the surface with ethanol before and after each use.
Laminar Air Flow can be vertical and horizontal. In the Vertical Laminar Air Flow the air blows down from the top of the cabinet. Vertical Laminar Air Flow is best for working with hazardous specimens since the aerosols that are generated in the cabinet are filtered out before they are released into the surrounding environments.
Horizontal Laminar Air Flow are designed such that the air flows directly at the operator hence they are not useful for working with hazardous specimens but are best protection for Tissue/cell culture.
Laminar Air Flow provides aseptic/sterile conditions for the preparation of Culture Media. All the culture vessels, test tubes, pipette, tip boxes, stocks of sterile eppendorfs should be opened only in the Laminar Air Flow to avoid any kind of contaminations. Culture Media cannot be prepared outside the Laminar Air Flow because it can get contaminated and there would not be any result

Seed Germinators

A seed germinator is Tissue/Cell Culture equipment. Using Seed Germinators, varying atmospheric conditions can be created within the chambers without the need of going outside. Typically, these create an environment in which light, humidity and temperature are controlled to provide optimum conditions for the germination of seeds. They are made of double walled structure having two chambers, one inner and one outer. The main components of a Seed Germinator include;

A germinating cylinder
A temperate controller

Seed Germinators are designed in such a way that they are able to control the crucial environmental parameters.


The Microscope is used for visualizing Tissue/Cell Cultures in situ. The cells in culture vessel remain at the bottom of the vessel and the medium floats above the growing cells. It is impossible to observe these cells under the ordinary Microscope; therefore, the Inverted Microscope is used for such purposes. The Inverted Microscope has the optical system at the bottom and the light source at the top, this arrangement helps to observe the cultured cells in the plates.

What is Lyophilization?

May 28th, 2014

Lyophilization/freeze drying is a method of extracting the water from Biological samples,foods and other products so that foods or products remain stable and are easier to store at room temperature. Biological materials should be dried to stabilize them for storage, preservation and shipping. In many cases this drying can cause damage and some loss of cellular or protein activity. Lyophilization significantly reduces damage to biological samples.

Principle of Lyophilization

Lyophilization is based on a simple principle of physics called “SUBLIMATION”. Sublimation is the process of transition of a substance from solid to the vapor state without passing through an intermediate liquid phase. The process of lyophilization consists of:

  • Freezing of the product to convert the water in the product to ice form,
  • Sublimation of ice directly into water vapor under vacuum.
  • Drawing off the water vapor
  • Once the ice has been sublimated, the products are freeze-dried and can be removed from machine.

The principle advantages of lyophilization as a drying process are:

  • Minimum damage and loss of activity in delicate heat-liable materials
  • Speed and completeness of rehydration
  • Possibility of accurate, clean dosing into final product containers
  • Porous, friable structure

The principle disadvantages of lyophilization are:

  • High capital cost of equipment (about three times more than other methods)
  • High energy costs (2-3 times more than other methods)
  • Long process time (typically 24 hour drying cycle)


Equipment used for Lyophilization – LYOPHILIZER

A lyophilizer consists of

  • A vacuum chamber containing product shelves which are capable of cooling and heating containers and their contents.
  • A vacuum pump, a refrigeration unit, which is associated controls are connected to the vacuum chamber.

Samples are generally placed in containers such as glass vials that are placed on the shelves within the vacuum chamber.

Cooling elements within the shelves freeze the product. Once the product is frozen, the vacuum pump evacuates the chamber and the product is heated. Heat is transferred by thermal conduction from the shelf, through the vial, and ultimately into the product.

Comparison with Liquid-Phase drying

Lyophilization avoid denaturation that is caused by heating the product, by maintaining it frozen throughout drying. This is the most obvious advantage over liquid-phase drying which cause the denaturation of proteins and other products.

Equally important is that in liquid-phase drying there is an undesirable shrinkage and concentration of active constituents that causes damage as well as a movement of these constituents to the surface of evaporation, where they form a dense, impermeable skin that inhibits drying, and later, rehydration. Such effects can be avoided by spray drying, but this requires brief exposure to temperatures around 100 degree C.

Advantages of the Lyophilization

Lyophilization has many advantages over the other drying and preserving techniques.

  1. It maintains food/ biochemical and chemical reagent quality because they remains at a temperature that is below the freezing-point during the process of sublimation.The use of lyophilization is particularly important when processing lactic bacteria, because these products are easily affected by heat.
  2. Food/biochemicals and chemical reagents which are lyophilized can usually be stored without refrigeration, which results in a significant reduction of storage and transportation costs.
  3. Lyophilization greatly reduces weight, and this makes the products easier to transport. For example, many foods contain as much as 90% water. These foods are 10 times lighter after lyophilization.
  4. Because they are porous, most freeze-dried products can be easily rehydrated. Lyophilization does not significantly reduce volume, therefore water quickly regains its place in the molecular structure of the food/ biochemicals and chemical reagents.

Safety Guidelines for Lyophilizer

  • Mammalian cells can not be preserved by lyophilization because it can desteoy mammalian cells. Many microorganisms and proteins survive lyophilization well,because they rehydrate easily and quickly because of the porous structure left after the ice sublimes.
  • Wear appropriate eye protection at all times when working with or near a lyophilizer.
  • Specimens shell-frozen in ampoules are dried on a vacuum manifold or in a chamber-type drier at low negative pressure. If the glass neck of the ampoule is sealed off while the ampoule is still under vacuum, it may cause implosion, either during the sealing or later when the evacuated ampoule is being opened. To avoid this, after drying is completed, and before sealing is done, bring the pressure within the ampoule back to normal by gradually introducing dry nitrogen, avoiding turbulent disturbance of the dry product.
  • The narrow or constricted neck of the ampoule is contaminated if the specimen is allowed to run down the wall of the neck during filling. Subsequently, when the ampoule is sealed with a torch, the dried material on the wall becomes charred or partially decomposed; residues of this material may adversely affect the dried material when it is reconstituted. To avoid this, a syringe with a long cannula or a Pasteur-type pipette should be used to fill the vial. Do not allow the delivery end of the cannula or pipette to touch the neck of the vial.
  • All ampoules used for freeze-drying of cultures, toxins, or other biohazardous material should be fabricated of Pyrex-type glass. This type of glass requires a high-temperature torch using an air-gas or oxygen-gas mixture for sealing. These hard glass ampoules are much less apt to form gas bubbles that burst inwardly during sealing under vacuum than the soft glass ampoules and are more resistant to breakage during handling and storage.
  • The filling of ampoules and vials with infectious specimens, the subsequent freeze-drying, and sealing or closing of ampoules and vials in the preparation of dry infectious specimens should be performed in a biological safety cabinet. The same is true for the preparation of ampoules and vials containing liquid specimens not subject to freeze-drying.

Safety precautions to be taken will depend on the agents, equipment, and containment available.