A 37−40% solution of formaldehyde in water is called formalin.
Formaldehyde Solution is a saturated solution of formaldehyde, water, and typically another agent, most commonly methanol. In its typical form, formalin is 37% formaldehyde by weight (40% by volume), 6-13% methanol, and the rest water.
It is a clear, colorless liquid with a strong, pungent odor, and it is commonly used as a disinfectant and preservative in medical and biological laboratories.

Formalin: Understanding the Preparation methods, Uses, Risks 

Other names

Formalin is also known as formaldehyde solution, formalin solution, or methanal solution.

Following a previous trade name, "formalin," "formaldehyde" was first used as a generic trademark in 1893.

Formalin is not a specific chemical compound, but rather a solution that contains formaldehyde gas dissolved in water, along with small amounts of methanol. The chemical formula for formaldehyde is CH2O or H-CHO, indicating that it consists of one carbon atom, two hydrogen atoms, and one oxygen atom. However, the formula for formalin is typically written as H2CO, which represents the chemical formula for formaldehyde as it is found in the aqueous solution.

History

Formalin was first discovered in the mid-19th century by the Russian chemist Aleksandr Butlerov. Butlerov synthesized formalin by reacting methyl alcohol (methanol) with calcium oxide (lime) and then passing the resulting gas through a tube.

Formalin was later independently synthesized by the German chemist August Wilhelm von Hofmann in the early 1860s. Hofmann obtained formalin by reacting methyl alcohol with formaldehyde gas, which is produced by the oxidation of methanol.

The use of formalin as a tissue fixative was first introduced in the late 19th century by the German physician Ferdinand Blum. Blum discovered that formalin could preserve tissues without destroying their structure or cellular morphology, making it a valuable tool in histology and pathology.

Formalin's use as a disinfectant and antiseptic was also recognized in the early 20th century, and it was widely used during World War I to treat wounds and prevent infection.

Characteristics of Formalin

Strong odor: Formalin has a pungent, irritating odor that is similar to the smell of formaldehyde gas. It is known to cause respiratory irritation and can be harmful when inhaled in high concentrations.

pH : The pH of formalin is typically around 7.0 to 7.5.

Disinfectant and preservative: Formalin is a powerful disinfectant and preservative due to its ability to crosslink proteins and other macromolecules, thus preventing decay and putrefaction. It is commonly used in medical and biological laboratories for this purpose.

Solubility: Formalin is soluble in water, which allows it to be easily mixed and diluted for use in various applications.

Hazardous substance: Formalin is considered to be a hazardous substance and should be handled with care. It can cause skin and eye irritation, respiratory problems, and is a potential carcinogen.

Stability: Formalin is relatively stable and has a long shelf life when stored properly. However, it can slowly decompose over time, releasing formaldehyde gas and becoming less effective as a disinfectant and preservative.

Working mechanism of formalin

Formalin is a solution of formaldehyde gas dissolved in water, with a small amount of methanol added to prevent polymerization of the formaldehyde. When formalin comes into contact with organic material, such as tissue or fruit, it reacts with the proteins and other biomolecules to form cross-links, which are covalent bonds that link different biomolecules together.

The cross-linking process occurs through a series of chemical reactions, which involve the aldehyde group of formaldehyde reacting with the amine groups of proteins and other biomolecules. Here is the chemical equation that represents the reaction of formaldehyde with an amine group:

HCHO + RNH2 → R-CH(OH)-NH2

In this reaction, formaldehyde (HCHO) reacts with an amine group (RNH2) to form a molecule that contains a methylene bridge (-CH2-) linking the two biomolecules together (R-CH(OH)-NH2).

This reaction can occur multiple times, resulting in the formation of a stable and hard polymer that can protect the tissue or fruit from decay and spoilage.

Preparation of Formalin

Formalin is a solution of formaldehyde gas dissolved in water, with a small amount of methanol added to prevent polymerization of the formaldehyde. It is typically prepared in a laboratory or industrial setting, and should be handled with care due to its hazardous nature. Here is a general procedure for preparing formalin:

Materials:   1. Formaldehyde gas

                     2. Distilled water

                     3. Methanol

Equipment:  1.Glass beaker or flask

                       2.Stirring rod

                       3.Scale

                       4.Safety equipment (gloves, goggles, etc.)

Procedure:

1. Calculate the amount of formaldehyde gas needed to prepare the desired concentration of formalin. Formalin typically contains 37% formaldehyde by volume, so you will need to determine the appropriate amount based on the volume of water you will be using.

2.Add the formaldehyde gas to a glass beaker or flask containing distilled water. Use a stirring rod to mix the solution until the formaldehyde gas is completely dissolved.

3.Add a small amount of methanol to the solution to prevent polymerization of the formaldehyde. The amount of methanol needed will depend on the concentration of formalin being prepared, but it is typically around 10% of the total volume.

4.Mix the solution thoroughly to ensure that the methanol is well distributed.

5.Store the formalin in a tightly sealed container, away from heat and light.

Note: It is important to handle formaldehyde and formalin with care, as they are hazardous substances. Always wear appropriate safety equipment and follow proper handling procedures when working with these chemicals.

The purpose of adding methanol to formalin

This reaction can occur multiple times, resulting in the formation of a stable and hard polymer that can protect the tissue or fruit from decay and spoilage.

The addition of methanol to formalin prevents the polymerization of formaldehyde, which can result in the formation of a solid precipitate that can clog laboratory equipment. Methanol acts as a stabilizing agent that helps to keep the formaldehyde in a liquid state and prevent the formation of solid particles. The reaction between formaldehyde and methanol is represented by the following equation:

HCHO + CH3OH ⇌ CH3OCH2OH

In this reaction, formaldehyde (HCHO) and methanol (CH3OH) react to form methylal (CH3OCH2OH), which is a stable liquid that helps to prevent the polymerization of formaldehyde.

Uses of formalin

1. Industrial industry: Formalin is used as a feedstock for the production of many industrial chemicals, including resins, plastics, textiles, and coatings. It is also used as a disinfectant in the food industry, and as a fumigant for storage areas and shipping containers.

2. Agriculture industry: Formalin is used as a pesticide and fumigant for crops, as it has insecticidal and fungicidal properties that help to protect crops from pests and diseases.

3. Beauty industry: Formalin is used in some hair smoothing and straightening products, as it helps to create a smooth, straight hair texture.

4. Medical industry: Formalin is widely used as a preservative and disinfectant for biological specimens in the medical and pathology fields. It is used to preserve tissues for microscopic examination, and it also has antimicrobial properties that help to prevent the growth of bacteria and other microorganisms.

5. Other industries: Formalin is also used in the manufacture of adhesives, paper products, and fire retardants.

Harmful effects of formalin on the human body

1. Irritation: Formalin is a strong irritant that can cause irritation and inflammation of the eyes, nose, throat, and skin.

2. Respiratory problems: Inhalation of formalin vapor can cause respiratory problems such as coughing, wheezing, shortness of breath, and chest tightness. Long-term exposure to formalin can potentially increase the risk of respiratory problems such as asthma.

3. Allergic reactions: Some people may develop allergic reactions to formalin, which can cause symptoms such as skin rash, hives, itching, and swelling.

4. Carcinogenicity: Formalin is classified as a carcinogen, which means that it has the potential to cause cancer. Long-term exposure to formalin has been associated with an increased risk of certain types of cancer, such as nasopharyngeal cancer and leukemia.

5. Neurological effects: Exposure to formalin can also cause neurological symptoms such as headache, dizziness, and confusion.

How formalin cause cancer

Formalin can react with DNA: Formalin is a reactive chemical that can bind to DNA and cause damage to the DNA structure. This can lead to mutations in the DNA that can disrupt normal cellular processes and potentially lead to cancer.

Formation of DNA adducts: When formalin reacts with DNA, it can form adducts, which are abnormal chemical structures that can interfere with DNA replication and transcription. These adducts can cause DNA damage, which can lead to mutations and potentially to cancer.

Activation of oncogenes: Formalin exposure has also been linked to the activation of oncogenes, which are genes that can promote the development of cancer. Formalin can trigger the expression of oncogenes through the formation of reactive oxygen species (ROS), which can cause oxidative stress and DNA damage.

Inhibition of tumor suppressor genes: Formalin exposure has been shown to inhibit the activity of tumor suppressor genes, which are genes that normally help to prevent the development of cancer. This inhibition can occur through the formation of adducts or through the interference with DNA replication and transcription.

Methods for detecting the presence of formalin in raw fish

Test kit : The kit contains a paper and liquid reagent. To test the fish, the paper has to be rubbed against the skin of the fish and the reagent has to be doped on the paper. If the paper turns blue, it is contaminated with ammonia or formalin, if it turns yellow it is free from contamination.

Chromatographic methods: Chromatographic methods such as high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) can be used to detect formalin in fish samples. These methods involve separating the components of the sample and identifying the presence and concentration of formalin.

Chemical tests: Chemical tests such as the Schiff's reagent test and the Nash reagent test can be used to detect formalin in fish samples. These tests involve adding a reagent to the fish sample that reacts with formalin and produces a color change or precipitate.

Biosensor-based methods: Biosensor-based methods involve using a biosensor to detect formalin in fish samples. These methods use biological molecules such as enzymes or antibodies that can bind specifically to formalin and produce a detectable signal