Care should be taken not to dispose in normal waste disposal systems. They should be properly segregated and handled according to the recommendation by experts.

Biological wastes that is not a regulated medical waste

Microbiological cultures must first be sterilized or disinfected in autoclaves or by chemical methods before disposal, carcasses, blood, and other biological specimens can be disposed by Burying, burning or incineration. Disposable biological instruments to be first sterilized in autoclave or dispose them by incineration.

Explain any four methods of laboratory waste disposal.

Burning
Burrying
Incineration
Dilluting and flushing through sinks

State for information to include while labeling laboratory solution and reagents

Name of the chemical ,
Its concentration,
Its storage requirements (if requires specific storage requirements),
its expiration date, if applicable

the hazards present.

State any four sources of water for laboratory work

The types of water used in laboratory processes and settings are defined, by the American Society for Testing and Materials (ASTM), into four grades: Type I, Type II, Type III and Type IV.

Type I: The purest type of water — used for cell culturing, gas chromatography, HPLC, tissue culturing, mass spectrometry and any other process requiring the highest levels of purity. Type I lab water is considered “ultrapure,” and must meet the following requirements:

Resistivity: Greater than 18 MΩ-cm

Conductivity: Less than 0.056 µS/cm

Total organic carbons: Less than 50 ppb

Type II: Not considered “ultrapure,” but still pure enough for specialized use, Type II is used for clinical analyzers, instrument feeds, electrochemistry and direct sample dilution — as well as for a feed to create Type I water. Type II water meets the following standards:

Resistivity: Greater than 1 MΩ-cm

Conductivity: Less than 1 µS/cm

Total organic carbons: Less than 50 ppb

(c) Type III: Produced from standard tap water using reverse osmosis, Type III water is a lower level of purity more suited for general use and as an initial stage for Type I or Type II water. Type III is used in rinsing and other preparation and secondary tasks. Type III water has the following properties:

Resistivity: Greater than 4 MΩ-cm

Conductivity: Less than 0.25 µS/cm

Total organic carbons: Less than 200 ppb

Type IV: Most often used as a feed to create more pure water,

Type IV water is produced through reverse osmosis to the following specs:

Resistivity: 200 KΩ-cm

Conductivity: Less than 5 µS/cm

Total organic carbons: No standard

Describe four categories of water impurities which necessitates its treatment before use in the laboratory

Solid impurities eg dust, fine sand, clay, dirt,
Biological contaminants eg microorganisms .
Chemical impurities eg heavy metal ions and , acids , bases and salts
Organic solvents

Describe the process of filtration in treatment of domestic water

Filtration is an essential step in the treatment of domestic water to remove impurities, particles, and contaminants. Here is a description of the process of filtration in the treatment of domestic water:

Coagulation/Flocculation: Before filtration, the water undergoes a process called coagulation/flocculation. Chemicals such as aluminum sulfate or ferric chloride are added to the water to create coagulation. These chemicals cause impurities and particles to clump together and form larger particles called flocs. Flocculants, such as polymers, may also be added to aid in the formation of flocs.
Sedimentation: After coagulation/flocculation, the water is allowed to sit in large sedimentation tanks. During this time, the flocs settle to the bottom of the tanks under the force of gravity. This process, known as sedimentation, allows the larger particles to separate from the water.
Filtration: The water is then passed through filters to remove any remaining suspended particles and impurities. Different types of filters are used, including:
Sand Filters: Sand filters consist of layers of graded sand and gravel. The water passes through these layers, and the sand and gravel act as physical barriers, trapping and removing fine particles, sediment, and larger impurities.
Activated Carbon Filters: Activated carbon filters contain granules of activated carbon, which have a large surface area and high adsorption capacity. These filters can effectively remove organic compounds, chlorine, and certain chemicals, improving the taste and odor of the water.
Multimedia Filters: Multimedia filters are made up of different layers of media, such as anthracite coal, sand, and garnet. Each layer has different sizes and densities, allowing for the removal of a wide range of impurities and particles.
Disinfection: After filtration, the water typically undergoes a disinfection process to kill or deactivate any remaining harmful microorganisms. Common methods of disinfection include chlorination, ultraviolet (UV) irradiation, or ozonation.
Additional Treatment: Depending on the quality of the water source and specific requirements, additional treatment processes such as pH adjustment, softening, or additional filtration steps may be included to ensure the water meets the desired quality standards.

It is important to note that the filtration process may vary depending on the specific water treatment plant and the source water quality. The objective is to remove suspended particles, turbidity, and certain contaminants to make the water safe and suitable for domestic use. Regular monitoring and testing of the treated water are crucial to ensure its quality and safety.

Describe three methods used in disinfecting water used in the laboratory

In laboratory settings, it is essential to ensure that the water used is free from microbial contaminants to maintain a sterile and safe environment. Here are three commonly used methods for disinfecting water in the laboratory:

Chemical Disinfection:

Chemical disinfection involves the use of chemicals to kill or inhibit the growth of microorganisms in water. Common disinfectants used in laboratories include chlorine-based compounds (e.g., sodium hypochlorite), iodine-based compounds (e.g., iodine tablets), or hydrogen peroxide. To disinfect water using chemicals, a predetermined dosage of the disinfectant is added to the water. The water is then allowed to sit for a specified contact time, typically recommended by the manufacturer or regulatory guidelines, to ensure sufficient disinfection. After the contact time, the water is considered disinfected and can be used for laboratory purposes.

UV Irradiation:

Ultraviolet (UV) irradiation is an effective method for disinfecting water by using UV light to kill or inactivate microorganisms. UV light damages the DNA and cellular structure of microorganisms, rendering them unable to reproduce. UV irradiation systems are installed in laboratory water supply systems, and water passes through a chamber where it is exposed to UV light. The exposure time depends on the flow rate and the intensity of the UV light. This method is effective against bacteria, viruses, and some protozoa.

Filtration:

Filtration is another method used to disinfect water in the laboratory. The filtration process physically removes microorganisms, particulate matter, and larger impurities from the water, reducing the microbial load. Different types of filters, such as membrane filters or depth filters, can be used in laboratory water systems. Membrane filters have pore sizes that effectively block the passage of microorganisms, while depth filters rely on a combination of physical entrapment and adsorption. Filtration should be used in conjunction with other disinfection methods to ensure comprehensive water treatment. Filtration alone may not be sufficient to eliminate all microbial contaminants, especially viruses, as their sizes can be smaller than the filter’s pore size.

It is important to note that the choice of disinfection method in the laboratory depends on factors such as the type and concentration of microorganisms present, water quality requirements, and specific laboratory protocols. Regular monitoring and validation of the disinfection process are essential to ensure the water is consistently disinfected and suitable for laboratory use.

Name any four contaminants removed during water treatment process

During the water treatment process, several contaminants are targeted and removed to ensure the water’s safety and quality. Here are four common contaminants that are typically removed during water treatment:

Suspended Solids: Suspended solids refer to particles or matter that are suspended in the water, such as sediment, silt, clay, and organic matter. These solids can make the water appear cloudy or turbid and can also harbor microorganisms. Filtration processes, including sedimentation and various filtration techniques, are used to remove suspended solids.
Bacteria and Viruses: Waterborne bacteria and viruses pose a significant health risk. They can cause various illnesses, including gastrointestinal infections. Disinfection methods like chlorination, UV irradiation, or ozone treatment are employed to kill or inactivate these microorganisms, ensuring the water is safe for consumption.
Organic Compounds: Organic compounds in water can come from various sources, including natural decomposition, industrial discharges, or agricultural runoff. These compounds may include pesticides, herbicides, industrial chemicals, and volatile organic compounds (VOCs). Activated carbon filters and other advanced treatment processes are used to remove or reduce the levels of organic compounds.
Chemical Contaminants: Chemical contaminants in water can arise from various sources, such as industrial activities, mining operations, or accidental spills. These contaminants may include heavy metals (e.g., lead, mercury, arsenic), nitrates, phosphates, fluoride, and various industrial chemicals. Specific treatment processes like coagulation, sedimentation, and activated carbon filtration are employed to remove or reduce the concentrations of these chemical contaminants.

It is important to note that the specific contaminants targeted and removed during the water treatment process may vary depending on the water source, local regulations, and the treatment techniques employed by the water treatment facility. Regular monitoring and testing of treated water are conducted to ensure compliance with safety standards and to address any emerging contaminants.

Describe the proper storage of the following chemicals in the laboratory

(a)Flammable chemicals

Protect container against physical damage, outside storage is most preferable, store in cool well-ventilated room away from any sources of ignition and direct sunlight. Isolate from other combustible materials. Place switches outside the store and use vapor proof bulbs for lighting.

Picric acid

Dry picric acid is very explosive; it reacts with metals to form explosive metal picrates which are highly sensitive to detonation. It explodes in the air and cause fire. Should be stored under water in ground neck glass stoppered bottles. Avoid friction, shock, or sudden heating which can initiate an explosion. There containers should not have metal caps since it vigorously react with it.

Radioactive chemicals

Store in sealed lead container, placed in thick wood or concrete, and kept in a locked cupboard situated away from the main building.

State four ideal conditions for storing chemicals sensitive to light.

Store in dark brown bottles

The bottles should have tightly fitting glass stoppers

Place them in dark cupboards

Place them Dark rooms

Briefly explain why concentrated sulphuric acid would be thought to be a potential source of danger in the laboratory.

Concentrated sulphuric acids are very corrosive and reactive and sometimes fuming.

Describe how to prepare Acidified potassium permanganate

Dissolve 3.2g of the salt in hot water, dilute to 1 liter, and filter through glass wool (0.01M). Add a few drops of sulphuric acid

Distinguish between the following terms
1. Molar and Normal solutions

(e.g., 1 M H₂SO₄= 2 N H₂SO₄)

Molar solution is defined as that which has its number ofmoles of solute dissolved in one liter of solution.

Normal solution is that which has the number of equivalents of solute dissolved in liter of solution.

Aqueous and colloidal solution

Aqueous solution is that which the solvent used is water and the solute size is too small and therefore mixes in water completely to form a clear solution. Colloidal solution is that solution in which the solute dissolved in water is relatively larger than water molecules but too small to be filtered out. However, due to its relative bigger size, colloidal solution will remain, as tiny molecules hence will not form a very clear as in aqueous solution.

Explain the safety precautions that must be observed when preparing the following solutions
- Sulfuric acid

Put on proper protective clothing.

Dissolve the acid in water and not water in acid.

Dissolve small volumes at a time.

Always allow the acid to flow through the walls of the water containing vessel (not to drop or pour directly into the water)

Shake the vessel constantly as you pour the acid.

Sodium hydroxide

Put on proper protective clothing.
Prepare in a well-ventilated room to avoid inhaling fumes
Dissolve little by little while stirring ( the process is very exothermic)

Describe how benedict solution is prepared.

Dissolve 200g sodium citrate, 75g sodium carbonate and 125g potassium thiocyanate in about 600 ml water. Dissolve separately, 18g copper (11) sulphate in 100 ml water. When the solutions have cooled, mix them together with stirring. Now add 5 ml of a 5% potassium ferrocyanide to the solution, and make up to 1 liter.

Explain
- Why glass stoppers stick when used to close flasks containing sodium hydroxide

Sodium hydroxide attacks or aches ground stoppered bottles causing to release some particles of glass which cause it to stick firmly and therefore not easy to be removed.

How the above glass stoppers can be removed

To remove, pour a few drops of dilute hydrochloric acid solution around the glass stopper, the acid will dissolve the particles and will loosen the stopper

Explain the importance of labeling laboratory solutions after preparation

All chemicals prepared in the laboratory must be labeled. Labels help people to easily identify the substance and alert people to the dangers of the product, and basic safety precautions.

State any four information that must be included in the labels

Label must contain the following information:
Product name
Information for the safe handling of the product
Hazard symbols
Risk phrases (words that describe the main hazards of the product)
First aid measures (what to do in an emergency)
For chemicals samples prepared in the lab , they must have the following additional details
Date of preparation.
Concentration prepared .
Name of the person who prepared it.

Explain the storage of the following materials in the laboratory
- Silver compoundsare very sensitive to light; they must therefore be kept away from light. They are also incompatible with, and therefore must be segregated from Acetylene, oxalic acid, tartaric acid, fulminic acid, ammonium compounds.
- Large quantity of gaseous flammable substances

Chemicals should be separated from each other by hazard class, whenever possible to avoid unwanted reactions in the event of a fire or due to leaking or broken containers. Acids should always be separate from cyanides and from bases, while oxidizers should always be kept away from organics and reducers. Carcinogens should be stored in ventilated cabinets. List the five hazard classes recommended for segregating chemicals in storage.

Acids, bases, flammables, oxidizers, reactives

State the storage of the following chemicals in the laboratory
- potassium

Potassium must always be stored under an inert atmosphere. Even when kept under mineral oil, a yellow coating of potassium superoxide may form after prolonged storage if oxygen is present in the headspace of the container.

concentrated sulfuric acid

Concentrated sulfuric acid should be stored in A stoppered ground bottles, in a cool, dry area away from direct sunlight and heat sources. Sulfuric acid should not be stored indoors in large quantities, to prevent the possible accumulation of vapors.

State the importance of incinerating solid wastes from a laboratory

Incineration method provides highest temperatures for burning which completely ensures that the solid waste have been completely burnt into ash while also ensuring that the toxic infectious fumes generated as a result of burning are safely routed out to the top atmosphere hence will not cause harm to the people around

Describe the storage of Helium

Helium cylinders should always be stored in a ventilated area, preferably a secure indoor area. It should not be stored in spaces that do not have protection from the weather. Prolonged storage in a wet or damp area could lead to rusting or weakening of the metal which may cause the helium cylinder to burst.

Explain how the following are prepared in the laboratory

Demineralize water

Demineralized water is devoid of all soluble mineral salts.

A demineralization water can be obtained by removing minerals from water, For this, ion exchange resins are used. First water is passed through cation exchange resin. Then water is passed through anion exchange resin.

When water is passed through cation exchange resin, cations, such as sodium, magnesium and calcium (from water to be demineralization) are exchanged with protons (from cation exchange resin). In this step, water becomes free from cations such as sodium, magnesium and calcium.

In the next step, water is passed through anion exchange resin, anions, such as chloride, bicarbonate and sulfate (from water to be demineralization) are exchanged with hydroxide (from anion exchange resin). In this step, water becomes free from anions such as chloride, bicarbonate and sulfate.Thus, the water obtained, is free from all soluble minerals.

Buffered water

Buffered water is water mixed with a chemical to give it special properties in regards to pH (acidity). The chemical, known as a buffer agent, resists pH changes when exposed to acids and bases when properly mixed in a solution.

Describe the quality control for distilled water in a laboratory

Test strips – These are small, single-use strips that change color to indicate the concentration of a specific chemical. Depending on the particular test, the user “activates” the paper or plastic strip by dipping it into the water sample and swishing it around, or by holding the strip in a stream of water. After waiting for a short time, the user compares the test strip color with a color chart to read the concentration of the chemical. These kits are extremely simple, but they are less accurate than other methods, especially if users don’t follow the instructions.
Color disk kits – Color disk test kits are available for a wide range of chemical tests. In a typical set-up, the user adds a powder packet or a few drops of a liquid reagent to a water sample in a reusable plastic tube. The user then places the sample tube in a small plastic viewing box. This viewing box contains a plastic disk with a color gradient printed on it. The user rotates the color disk to find the part that best matches the color of the sample, and then reads the concentration of the chemical from the disk. Color disk kits typically have multiple steps and often include prescribed wait times, so they’re a little more complicated and costly, but generally more accurate.
Hand-held digital instruments – Lightweight and portable digital meters, colorimeters, and photometers are available for water testing. They provide the most accurate results of these three testing methods, but they are also more expensive and delicate than the previous options. These instruments require batteries and calibration. While digital instruments are helpful to field technicians and are an essential part of any continuous or remote monitoring network,
Chemical quality control

Various chemical methods of quality control are also available for testing presence of various soluble and non soluble substances in waster as well as heavy metal

List three examples of flammable chemicals

All liquid with a flash point under 100°F are considered flammable. Examples: gasoline, acetone, toluene, diethyl ether, alcohols.

Highlight four features of an inflammable liquid store

Flammable and combustible liquids ignite easily and burn with extreme rapidity.
Flammability is determined by the flash point of a material.
Flash point is the minimum temperature at which a liquid forms a vapor above its surface in sufficient concentration that it can be ignited.
Flammable liquids have a flash point of less than 100°F. Liquids with lower flash points ignite easier.
Combustible liquids have a flashpoint at or above 100°F.
The vapor burns, not the liquid itself. The rate at which a liquid produces flammable vapors depends upon its vapor pressure.
The vaporization rate increases as the temperature increases. Therefore, flammable and combustible liquids are more hazardous at elevated temperatures than at room temperature.

Describe the proper disposal of the following
1. Corrosive chemicals

They must be diluted in plenty of water before discharging them through sink

Radioactive chemicals

Radioactive substances are usually collected in stores then periodically shipped to disposal centers.

Care should be taken not to dispose in normal waste disposal systems. They should be properly segregated and handled according to the recommendation by experts.

Biological wastes that is not a regulated medical waste

Explain any four methods of laboratory waste disposal.

Burning
Burrying
Incineration
Dilluting and flushing through sinks

Describe the proper storage of the following chemicals in the laboratory

(a)Flammable chemicals

Picric acid

Radioactive chemicals

Store in sealed lead container, placed in thick wood or concrete, and kept in a locked cupboard situated away from the main building.

State four ideal conditions for storing chemicals sensitive to light.

Store in dark brown bottles
The bottles should have tightly fitting glass stoppers
Place them in dark cupboards
Place them Dark rooms

All lab workers generating hazardous waste should should set up and follow a waste minimization program. Minimizing wastes also minimizes safety hazards. List several procedures for minimizing hazardous waste.
- Periodically inspect inventory of chemicals and discard those which are outdated or for which you have no further use.
- Avoid purchasing larger quantities than needed.
- Check the departmental chemical inventory lists for items before ordering from an outside vendor.
- Minimize the amount of required materials — can the experiment be performed on a smaller scale?
- Substitute less hazardous materials for more hazardous materials used in experiments.
- Before accepting “donations”, know what the material is and its age, and ask yourself if you can really use it.
Briefly explain why concentrated sulphuric acid would be thought to be a potential source of danger in the laboratory.

Concentrated sulphuric acids are very corrosive and reactive and sometimes fuming.

Describe how to prepare Acidified potassium permanganate

Dissolve 3.2g of the salt in hot water, dilute to 1 liter, and filter through glass wool (0.01M). Add a few drops of sulphuric acid

Distinguish between the following terms
- Molar and Normal solutions

(e.g., 1 M H₂SO₄= 2 N H₂SO₄)

Molar solution is defined as that which has its number ofmoles of solute dissolved in one liter of solution.

Normal solution is that which has the number of equivalents of solute dissolved in liter of solution.

Aqueous and colloidal solution

Explain the safety precautions that must be observed when preparing the following solutions
- Sulfuric acid

Put on proper protective clothing.
Dissolve the acid in water and not water in acid.
Dissolve small volumes at a time.
Always allow the acid to flow through the walls of the water containing vessel (not to drop or pour directly into the water)
Shake the vessel constantly as you pour the acid.
- Sodium hydroxide
Put on proper protective clothing.
Prepare in a well-ventilated room to avoid inhaling fumes
Dissolve little by little while stirring ( the process is very exothermic)

Describe how benedict solution is prepared.

Explain
- Why glass stoppers stick when used to close flasks containing sodium hydroxide

Sodium hydroxide attacks or aches ground stoppered bottles causing to release some particles of glass which cause it to stick firmly and therefore not easy to be removed.

(b) How the above glass stoppers can be removed

To remove, pour a few drops of dilute hydrochloric acid solution around the glass stopper, the acid will dissolve the particles and will loosen the stopper

Describe the laboratory waste disposal general rules

Minimise waste and do not accumulate large amounts in the laboratory.
Regular disposal from the laboratories must be part of the laboratory program.
Segregate waste – have a separate residue container if you are generating a large amount of any particular type of waste. Ensure the waste container is compatible with the waste you are collecting.
Label the waste residue container with the appropriate waste label.
Store waste in a suitable area prior to collection. For example, chemicals and solvents should be stored in ventilated areas and residue container lids must be secure.
Ensure container is not leaking and no spillage on the exterior of the container.
Handle waste only if you are aware of the hazards associated with the waste and appropriate risk controls are used.
Dispose waste as per relevant waste disposal guidelines.
Record all disposal on Waste Tracking Log to ensure evidence of correct waste management.

Explain the importance of labeling laboratory solutions after preparation

All chemicals prepared in the laboratory must be labeled. Labels help people to easily identify the substance and alert people to the dangers of the product, and basic safety precautions.

(b) State any four information that must be included in the labels

Label must contain the following information:
Product name
Information for the safe handling of the product
Hazard symbols
Risk phrases (words that describe the main hazards of the product)
First aid measures (what to do in an emergency)
For chemicals samples prepared in the lab , they must have the following additional details
Date of preparation.
Concentration prepared .
Name of the person who prepared it.

State the storage of the following chemicals in the laboratory
1. potassium

concentrated sulfuric acid

State the importance of incinerating solid wastes from a laboratory

State four types of waste disposal in the laboratory

Burning
Burrying
Incineration
Dilute and flash

Describe four categories of water impurities which necessitate its treatment before use in laboratories

The types of impurities in water can include dust, dirt, harmful chemicals, biological contaminants, radiological contaminants, and total suspended solids (TSS).

Describe systematically the process of chemical water treatment.

General steps in purification of drinking water includes

Step 1. Aeration:

Raw water is first collected in large aeration tank and the water is aerated by bubbling compressed air through perforated pipes.
Aeration removes bad odors and CO2. It also removes metal such as iron, manganese by precipitating then as their respective hydroxides.

Step 2. Storage or settling:

Aerated water is then placed in settling tank and stored for 10-14 days.
During storage about 90% of suspended solids settle down within 24 hrs and the water becomes clear.
Certain heavier toxic chemicals also settle down during storage.
Similarly pathogenic bacteria gradually die and bacterial count decreases by 90% in first in first 5-7 days of storage.
During storage organic matter present in water is oxidized by microorganisms. Similarly NH3 present is oxidized into nitrate by microorganisms during storage.

Step 3. Coagulation:

Water from storage tank is then placed in coagulation tank and then some precipitating agents such as alum, lime etc. are added in water and mixed.
These precipitating agents form precipitate of Al(OH)3 when dissolved in water.
Suspended solids absorbs on the surface of precipitate, so gradually mass of precipitate becomes heavier and finally settle down.
This technique is used to remove very light suspended solids that do not settle by themselves during storage. Furthermore, if negatively charged colloidal impurities are present, they are neutralized by Al³⁺ions and settle down.

Step 4. Filtration:

Partially clarified water is then passed through sand gravity filter which removes 98-99% of microorganisms and other impurities.
Sand gravity water filter:
- Sand filter is a rectangular tank in which filter bed is made up to 3 layers.
- Top layer: fine layer of 1 meter thick
- Middle layer: 0.3-0.5 meter thick layer of coarse sand
- Bottom layer: 0.3-0.5 meter thick layer of gravel
There is a collection tank at the bottom of the filter bed to collect filtered water. During filtration filter bed soon gets covered with a slimy layer called vital layer.
Vital layer consists of thread like algae, diatoms and bacteria.
During filtration microorganisms presents in vital layer oxidize organic and other matter present in water. For example if NH3 is present, it is oxidized into nitrate.
Vital layer also helps in filtration of microbial cells.
If water contains unpleasant odor, activated carbon may be placed in filter bed that removes bad odors.

Step 5. Disinfection:

The filtered water is finally purified by using disinfectants. eg. Chlorination
Disinfectant kills pathogenic as well as other microorganism in water.
After disinfection water is pumped into overhead tank for subsequent domestic distribution.

List any four classes of fixatives based on their mechanism of action

The purpose of fixation is to preserve tissues permanently in as life-like a state as possible. Fixation should be carried out as soon as possible after removal of the tissues (in the case of surgical pathology) or soon after death (with autopsy) to prevent autolysis. There is no perfect fixative, though formaldehyde comes the closest. Therefore, a variety of fixatives are available for use, depending on the type of tissue present and features to be demonstrated.

There are five major groups of fixatives, classified according to mechanism of action:

Aldehydes include formaldehyde (formalin) and glutaraldehyde. Tissue is fixed by cross-linkages formed in the proteins, particularly between lysine residues. This cross-linkage does not harm the structure of proteins greatly, so that antigenicity is not lost. Therefore, formaldehyde is good for immunohistochemical techniques. Formalin penetrates tissue well, but is relatively slow. The standard solution is 10% neutral buffered formalin. A buffer prevents acidity that would promote autolysis and cause precipitation of formol-heme pigment in the tissues.

Glutaraldehyde causes deformation of alpha-helix structure in proteins so is not good for immunohistochemical staining. However, it fixes very quickly so is good for electron microscopy. It penetrates very poorly, but gives best overall cytoplasmic and nuclear detail. The standard solution is a 2% buffered glutaraldehyde

Mercurials fix tissue by an unknown mechanism. They contain mercuric chloride and include such well-known fixatives as B-5 and Zenker’s. These fixatives penetrate relatively poorly and cause some tissue hardness, but are fast and give excellent nuclear detail. Their best application is for fixation of hematopoietic and reticuloendothelial tissues. Since they contain mercury, they must be disposed of carefully.

Alcohols, including methyl alcohol (methanol) and ethyl alcohol (ethanol), are protein denaturants and are not used routinely for tissues because they cause too much brittleness and hardness. However, they are very good for cytologic smears because they act quickly and give good nuclear detail. Spray cans of alcohol fixatives are marketed to physicians doing PAP smears, but cheap hairsprays do just as well.

Oxidizing agents include permanganate fixatives (potassium permanganate), dichromate fixatives (potassium dichromate), and osmium tetroxide. They cross-link proteins, but cause extensive denaturation. Some of them have specialized applications, but are used very infrequently.

Picrates include fixatives with picric acid. Foremost among these is Bouin’s solution. It has an unknown mechanism of action. It does almost as well as mercurials with nuclear detail but does not cause as much hardness. Picric acid is an explosion hazard in dry form. As a solution, it stains everything it touches yellow, including skin

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