Introduction to Phenol-Chloroform Method of DNA Extraction
The Phenol‑Chloroform Method of DNA Extraction is a classical laboratory technique used to isolate DNA from cells by separating nucleic acids from proteins and other cellular components based on their different solubilities in aqueous and organic solvents.
In this method, the process begins with cell lysis, where cells are broken open to release their internal components, including DNA, RNA, proteins, lipids, and other biomolecules.
After the cells are lysed, the mixture is treated with a phenol : chloroform : isoamyl alcohol solution, which acts as an organic solvent system designed to separate biomolecules into different phases.
During centrifugation, the mixture separates into two distinct layers because of differences in polarity and solubility.
Proteins, lipids, and cellular debris move into the organic phase, which contains phenol and chloroform.
DNA and RNA remain in the upper aqueous (water-based) layer, since nucleic acids are more soluble in the polar aqueous environment.
The aqueous layer containing nucleic acids is carefully collected, usually using a pipette, while avoiding disturbance of the interphase where denatured proteins accumulate.
The extracted DNA is then precipitated and purified, typically using alcohol such as ethanol or isopropanol, allowing the DNA to be collected for further analysis.
This method produces high-quality and intact DNA, making it suitable for various molecular biology applications.
The purified DNA obtained through this method can be used for restriction enzyme analysis, cloning experiments, and DNA sequencing.
The effectiveness and reliability of this method have made it a widely used technique in molecular biology laboratories (Brown, 2020).
Key Reagents of the Phenol‑Chloroform Method of DNA Extraction
EDTA (0.6 M) – Typically 1 mL per 14 mL sample for biological fluids. EDTA acts as a chelating agent that binds divalent cations such as Mg²⁺ and Ca²⁺, which are essential cofactors for DNases. By removing these ions, EDTA inhibits DNase activity and helps stabilize DNA, preventing degradation during extraction.
Extraction Buffer (50 mM Tris-Cl pH 8.0, 100 mM NaCl, 10 mM EDTA, 0.5 % SDS, 0.2 mg mL⁻¹ Proteinase K, 1 % 2-mercaptoethanol) – Used in an amount sufficient to submerge tissue, typically around 500 µL per 50–100 mg of tissue. This buffer performs several functions simultaneously: Tris-Cl maintains a stable pH environment, EDTA chelates metal ions, SDS disrupts lipid membranes and lyses cells, Proteinase K digests proteins, NaCl helps maintain ionic strength, and 2-mercaptoethanol reduces disulfide bonds in proteins, aiding in protein denaturation and improving DNA release.
Phosphate Buffered Saline (PBS) – Usually 500 µL per sample. PBS is used to resuspend the cell pellet and maintain isotonic conditions before cell lysis, ensuring cells remain intact until the lysis step begins.
10 % SDS (Sodium Dodecyl Sulfate) – Included in the lysis buffer. SDS is a strong anionic detergent that solubilizes lipid membranes and denatures proteins, helping to break open cells and release nucleic acids.
Proteinase K (20 mg mL⁻¹ stock) – Added to the lysis buffer at a final concentration of about 0.2 mg mL⁻¹. Proteinase K is a broad-spectrum protease that hydrolyzes proteins, including nucleases and histones, which facilitates efficient release and protection of DNA.
RNase A (10 mg mL⁻¹) – Typically 5 µL added per sample, followed by incubation for about 45 minutes at 37 °C. RNase A degrades RNA molecules, ensuring that the final preparation contains pure DNA without RNA contamination.
Phenol : Chloroform : Isoamyl Alcohol (25 : 24 : 1) – Added in an equal volume to the lysate, usually around 0.5–1 mL. Phenol denatures proteins, chloroform enhances phase separation between aqueous and organic layers, and isoamyl alcohol reduces foaming during mixing, allowing efficient removal of proteins and cellular debris.
Chloroform (100 %) – Added in a volume equal to the aqueous phase after the initial extraction. This step helps remove residual phenol from the aqueous DNA layer, improving purity and preventing phenol contamination in the final DNA sample.
3 M Sodium Acetate (pH 5.2) – Typically 1/10 volume of the aqueous phase is added. Sodium acetate provides Na⁺ ions that neutralize the negatively charged phosphate backbone of DNA, which promotes DNA aggregation and efficient precipitation when ethanol is added.
100 % Ethanol (chilled) – Added at twice the volume of the aqueous phase. Cold ethanol precipitates DNA, allowing it to aggregate and form a visible pellet during centrifugation.
70 % Ethanol (chilled) – Used for two washes of the DNA pellet. These washes remove residual salts, phenol traces, and other organic contaminants, improving the purity of the extracted DNA.
TE Buffer (10 mM Tris-Cl pH 8.0, 1 mM EDTA) – Approximately 50 µL is used to resuspend the DNA pellet. TE buffer solubilizes DNA for storage, where Tris maintains a stable pH and EDTA protects DNA by inhibiting nucleases.
Principle of the Phenol-Chloroform Method of DNA Extraction
The phenol–chloroform method is based on the differential solubility of biomolecules in aqueous and organic solvents, allowing efficient separation of DNA from proteins and other cellular components.
Phenol, which is a polar organic solvent, disrupts hydrogen bonds and hydrophobic interactions in proteins, leading to their denaturation and causing them to migrate into the organic phase during extraction.
Chloroform enhances the clarity and sharpness of phase separation, allowing a distinct boundary between the organic and aqueous layers, which makes it easier to isolate the nucleic acid-containing phase.
Isoamyl alcohol is included in the mixture primarily to reduce excessive foaming during mixing, ensuring smoother handling and better phase separation during centrifugation.
DNA and RNA remain dissolved in the aqueous (water-based) layer because their negatively charged phosphate backbone interacts strongly with water molecules, which stabilizes nucleic acids in the polar aqueous environment.
During centrifugation, the mixture separates into two main layers, where the upper aqueous phase contains nucleic acids, while proteins, lipids, and other contaminants accumulate in the organic layer or at the interphase.
After isolating the aqueous phase, ethanol is added along with sodium ions, typically supplied by sodium acetate, to facilitate DNA precipitation.
The sodium ions neutralize the negative charges on the DNA phosphate backbone, reducing electrostatic repulsion between DNA molecules.
This allows the DNA strands to aggregate and form a visible pellet when ethanol is present, particularly at low temperatures.
The resulting DNA pellet can then be collected by centrifugation, leaving behind most contaminants in the solution and producing purified DNA suitable for downstream molecular biology applications (Brown, 2020).
Protocol of the Phenol‑Chloroform Method of DNA Extraction
A. Sample Preparation
For biological fluids and culture media, transfer 7 mL of the sample into a tube pre-filled with 0.51 mL of 0.6 M EDTA.
Centrifuge at 15,000 g for 15 minutes, then discard the supernatant.
If the cell pellet is not visible, repeat the centrifugation step until a pellet forms.
For tissue samples, add small pieces of tissue into the extraction buffer composed of 50 mM Tris-Cl (pH 8.0), 100 mM NaCl, 10 mM EDTA, 0.5 % SDS, 0.2 mg mL⁻¹ Proteinase K, and 1 % 2-mercaptoethanol.
Homogenize the tissue on ice using a mortar and pestle until no large pieces remain, ensuring that foaming is avoided during homogenization (Kathmandu University, 2025).
B. Cell Lysis
Resuspend the pellet in 500 µL of PBS if the sample needs to be temporarily stored before lysis.
Add 700 µL of prepared lysis buffer containing 10 % SDS and Proteinase K.
Vortex the mixture for 1 minute to ensure proper mixing and disruption of cell structures.
Add 5 µL of RNase A (10 mg mL⁻¹) to remove RNA contamination.
Incubate at 37 °C for 45 minutes, gently inverting the tube every 10 minutes to ensure uniform digestion.
C. Phenol-Chloroform Extraction
Add an equal volume of phenol : chloroform : isoamyl alcohol (25 : 24 : 1) to the lysate.
Mix gently by inversion for approximately 30 seconds to allow proper interaction between phases.
Centrifuge at 16,000–18,000 g for 5 minutes at room temperature.
After centrifugation, three distinct layers appear:
Bottom organic layer: phenol and chloroform containing denatured proteins.
Middle interphase: a white layer composed of protein debris.
Top aqueous layer: contains dissolved DNA.
Carefully pipette the upper aqueous layer into a fresh tube without disturbing the interphase.
Repeat the extraction step two to three times until the interphase appears clear, indicating effective removal of proteins.
D. Phenol Removal and DNA Precipitation
Add an equal volume of chloroform to the final aqueous layer to remove any residual phenol contamination.
Mix gently and centrifuge again under the same conditions.
Transfer the clean aqueous phase into a new tube.
Add one-tenth volume of 3 M sodium acetate followed by two volumes of chilled 100 % ethanol.
Mix by gentle inversion and incubate on ice for about 20 minutes to promote DNA precipitation.
E. DNA Recovery
Centrifuge at 16,000 g at 4 °C for 15 minutes to pellet the DNA.
Discard the supernatant carefully without disturbing the pellet.
Wash the DNA pellet twice with chilled 70 % ethanol to remove salts and residual contaminants.
Air-dry the pellet briefly for up to 10 minutes to remove remaining ethanol.
Resuspend the DNA pellet in 50 µL of TE buffer.
Store the purified DNA at –20 °C for long-term preservation.
F. Optional Clean-up
If significant protein contamination is suspected, perform an additional phenol-chloroform extraction step before ethanol precipitation to further improve DNA purity.
Modifications of the Phenol‑Chloroform Method of DNA Extraction
Carrier-aided precipitation: The addition of carriers such as glycogen or linear polyacrylamide can significantly improve DNA recovery from low-concentration or dilute samples. These carriers act as co-precipitants, helping DNA molecules aggregate more efficiently during alcohol precipitation and making the DNA pellet easier to visualize and recover (Liu et al., 2022).
Isopropanol substitution: In some protocols, 2-propanol (isopropanol) is used instead of ethanol for DNA precipitation. Typically, 0.7× the volume of isopropanol relative to the aqueous phase is sufficient to precipitate DNA. This modification can accelerate DNA precipitation, particularly in dilute lysates, and often requires less volume compared to ethanol (Liu et al., 2022).
Magnetic bead capture: Instead of relying solely on centrifugation-based phase separation and precipitation, silica-coated magnetic beads can be used to bind DNA after cell lysis. The beads are then separated using a magnetic field, allowing the bound DNA to be washed and purified rapidly, which reduces multiple centrifugation steps and simplifies the workflow (Green & Sambrook, 2017; Liu et al., 2022).
CTAB pre-treatment for plant tissues: For samples rich in polysaccharides and plant secondary metabolites, a pre-treatment step using cetyltrimethylammonium bromide (CTAB) may be applied. CTAB forms an insoluble DNA–CTAB complex, which helps separate DNA from carbohydrates and other contaminants. The complex is subsequently dissolved in 1 M NaCl before phenol extraction, allowing efficient recovery of purified DNA from plant tissues (Van der Merwe, 2019).
Troubleshooting of the Phenol‑Chloroform Method of DNA Extraction
Low DNA yield
Likely cause: Incomplete cell lysis or insufficient DNA precipitation.
Solution: Increase SDS concentration to about 1 % (w/v) or introduce an additional freeze–thaw cycle to improve cell disruption (protocol.io). Extend Proteinase K digestion (20 mg mL⁻¹) for about 1 hour at 55 °C to enhance protein degradation. Ensure efficient precipitation by maintaining an ethanol-to-sample ratio of ≥ 2.5 : 1, or alternatively add 0.7 volume of isopropanol to facilitate DNA precipitation (Bite-size Bio).
Protein contamination
Likely cause: Insufficient phenol extraction steps leading to incomplete removal of proteins.
Solution: Perform 3–4 sequential phenol-chloroform extraction steps to ensure proper protein removal. Additionally, pre-treat the lysate with Proteinase K (20 mg mL⁻¹) and, if contamination persists, include a second enzymatic digestion using Pronase to further degrade residual proteins (CSH Protocols).
Phenol carry-over (orange tint in aqueous phase)
Likely cause: Incomplete removal of phenol due to insufficient chloroform washing.
Solution: Perform an additional chloroform–isoamyl alcohol wash to remove residual phenol. Using Phase-Lock Gel tubes can also help prevent interphase contamination and phenol bleed-through into the aqueous layer (Bite-size Bio).
Sheared DNA
Likely cause: Vigorous vortexing or excessive mechanical agitation during extraction.
Solution: Avoid harsh mixing; instead mix gently by inversion or rotate the tubes slowly (≤ 20 rpm) to preserve DNA integrity (CSH Protocols). When working with soil samples, limit bead-beating to ≤ 2 minutes to minimize DNA fragmentation.
RNA contamination
Likely cause: Insufficient RNase treatment or inactive enzyme.
Solution: Increase RNase A concentration to approximately 10 µg mL⁻¹ and incubate the sample for about 30 minutes at 37 °C. Confirm RNase activity using a control RNA sample, and maintain RNase-free tips, tubes, and work surfaces to prevent contamination (Bite-size Bio).
Solution: Use chloroform chilled to about 4 °C and ensure phenol is properly equilibrated to pH 7.8–8.0. Adding an extra 0.1 volume of 3 M sodium acetate before extraction can improve phase separation (protocol.io).
Small or invisible DNA pellet
Likely cause: Very low DNA concentration, over-drying of the pellet, or absence of precipitation carriers.
Solution: Add 1 µg glycogen or about 10 µg linear polyacrylamide as a carrier before precipitation to improve pellet formation. Avoid air-drying the pellet for more than 10 minutes, and always use cold ethanol (around −20 °C) during precipitation to maximize DNA recovery.
Humic-acid or polysaccharide contamination (A₂₆₀/A₂₃₀ < 1.8)
Likely cause: Extraction from soil or plant matrices rich in organic inhibitors.
Solution: Include a CTAB pre-extraction step when processing plant tissues to remove polysaccharides. After phenol extraction, perform an additional chloroform wash and optionally apply PVPP column clean-up to remove inhibitory compounds (protocol.io).
DNA degradation (smearing on gel electrophoresis)
Likely cause: Prolonged exposure of DNA to phenol at room temperature.
Solution: Carry out extraction at approximately 4 °C whenever possible and keep samples on ice during phase separation to minimize DNA degradation.
Residual ethanol after washing
Likely cause: Incomplete removal of ethanol during the washing step.
Solution: After the final 70 % ethanol wash, centrifuge for about 5 minutes at 14,000 g, then invert the tube on a lint-free tissue to blot remaining ethanol before allowing the pellet to air-dry. Using Phase-Lock Gel tubes may further reduce solvent carry-over.
Quality Assessment of the Phenol‑Chloroform Isolated DNA
Spectrophotometry: DNA purity is commonly evaluated using spectrophotometric absorbance ratios. An A₂₆₀/A₂₈₀ ratio of approximately 1.8 generally indicates minimal protein contamination, whereas an A₂₆₀/A₂₃₀ ratio of ≥ 2.0 suggests low levels of polysaccharides, phenol, or other organic solvent contaminants. These ratios help determine whether the extracted DNA is sufficiently pure for downstream molecular applications such as PCR, cloning, or sequencing (Brown, 2020; Green & Sambrook, 2017).
Agarose Gel Electrophoresis: DNA integrity can be examined by running the extracted DNA on a 0.8% agarose gel. High-molecular-weight DNA typically appears as a bright band near the top of the gel, with minimal smearing, which indicates that the DNA is intact and has not undergone significant degradation (Brown, 2020; Liu et al., 2022).
Fluorometric quantification: DNA concentration can be measured more accurately using fluorescence-based methods such as the Qubit dsDNA HS Assay. This method is particularly useful for low-yield or precious samples, as it provides high sensitivity and specificity for double-stranded DNA, reducing interference from RNA, proteins, or other contaminants (Liu et al., 2022).
Safety Tips and Precautions of the Phenol‑Chloroform Method of DNA Extraction
Personal Protective Equipment (PPE): Always wear appropriate laboratory safety equipment, including a lab coat, nitrile gloves (preferably double-gloving), and chemical splash goggles or a face shield. Phenol and chloroform are hazardous chemicals; phenol can cause severe chemical burns, and chloroform vapors can cause irritation and systemic toxicity. Additionally, phenol and chloroform can penetrate latex gloves, which is why nitrile gloves are recommended (Green & Sambrook, 2017; Reina, 2025).
Ventilation: All procedures involving phenol and chloroform should be conducted inside a certified chemical fume hood. Phenol is highly corrosive, while chloroform is hepatotoxic and considered potentially carcinogenic, making proper ventilation essential to prevent inhalation exposure (Green & Sambrook, 2017; Liu et al., 2022).
Automation advantage: The use of robotic or enclosed nucleic acid extraction systems can significantly reduce direct exposure to phenol and chloroform vapors. Automated systems also minimize manual handling during phase separation, which improves safety and reduces the risk of contamination or accidental exposure (Liu et al., 2022).
Temperature safety: Phenol should be stored chilled at approximately 4 °C in secondary containment to maintain reagent stability and preserve DNA integrity during extraction procedures. Keeping phenol cold also reduces volatilization and vapor formation. However, phenol should not be frozen, as freezing may cause crystallization and potential rupture of storage containers (Green & Sambrook, 2017).
Waste disposal: Phenol–chloroform mixtures should be disposed of in properly labeled halogenated organic solvent waste containers. Before disposal, residual phenol may be neutralized using sodium hydroxide (NaOH) according to institutional chemical safety and biosafety guidelines (Green & Sambrook, 2017; Van der Merwe, 2019).
Spill management: In the event of a spill, absorb the chemical immediately using inert absorbent materials such as vermiculite or chemical spill pads. The contaminated area should then be rinsed thoroughly with large amounts of water for at least 15 minutes. Direct skin contact must be avoided, and any exposure incidents should be reported immediately according to laboratory safety protocols (Green & Sambrook, 2017).
Storage and Long‑Term Stability of Phenol‑Chloroform Isolated DNA
Short-term storage: Purified DNA in the aqueous phase can be stored at 4 °C for up to one week. Keeping the DNA at this temperature helps minimize nuclease activity and maintains DNA integrity for immediate downstream molecular biology applications such as PCR, cloning, or sequencing (Green & Sambrook, 2017).
Long-term storage: For extended preservation, DNA should be aliquoted in TE buffer (10 mM Tris-HCl, 1 mM EDTA, pH 8.0) and stored at –20 °C or –80 °C. The Tris buffer stabilizes pH, while EDTA chelates divalent metal ions, thereby inhibiting nuclease activity that could degrade DNA. It is important to avoid repeated freeze–thaw cycles, as these can cause DNA strand shearing and depurination, reducing DNA quality over time (Liu et al., 2022).
Phenol-containing extracts: If DNA remains in a phenol-containing phase after extraction, it should be stored at 4 °C for no longer than 48 hours before proceeding to ethanol precipitation. Over time, phenol can oxidize, forming reactive compounds that may damage DNA and inhibit enzymatic reactions such as polymerase activity (Van der Merwe, 2019; Green & Sambrook, 2017).
Ethanol preservation: For field sampling or long-term archival storage, DNA pellets may be stored in 70–100 % ethanol at –20 °C. Ethanol storage helps reduce hydrolytic degradation and prevents microbial growth, thereby maintaining DNA stability for extended periods until further processing (Liu et al., 2022).
Applications of the Phenol‑Chloroform Method of DNA Extraction
Genomic DNA isolation: This method produces high-quality genomic DNA that is suitable for multiple molecular biology applications, including restriction mapping, genomic library construction, and whole-genome sequencing. The technique effectively removes proteins and other contaminants, allowing the recovery of highly purified DNA for downstream analyses (Green & Sambrook, 2017; Liu et al., 2022).
RNA-free DNA for epigenetic studies: The protocol allows the complete removal of RNA using RNase treatment, resulting in highly purified DNA preparations. RNA-free DNA is particularly important for epigenetic research, including DNA methylation analysis and bisulfite-conversion assays, where RNA contamination can interfere with accurate results (Green & Sambrook, 2017).
High-molecular-weight DNA recovery: The phenol-chloroform method is capable of recovering intact, high-molecular-weight DNA, sometimes reaching megabase-sized fragments. This makes it valuable for samples that are degraded or difficult to process, such as forensic tissues, plant residues, and ancient biological specimens, where maintaining DNA integrity is critical (Liu et al., 2022).
Viral and environmental nucleic acids: The method is widely used to obtain highly purified viral or microbial DNA from environmental samples such as soil and water. The resulting DNA is compatible with infectivity assays, microbial diversity studies, and metagenomic sequencing, enabling researchers to study microbial communities and environmental pathogens (Van der Merwe, 2019).
Advantages of the Phenol‑Chloroform Method of DNA Extraction
Cost-effective: This method relies on inexpensive and readily available laboratory reagents, making it a budget-friendly alternative to commercial DNA extraction kits such as silica column–based or magnetic bead–based systems. Because it does not require proprietary consumables, it is widely used in research laboratories with limited resources (Green & Sambrook, 2017).
High yield and integrity: The phenol-chloroform extraction technique can produce large quantities of DNA with minimal fragmentation, provided that the sample is handled gently during mixing and phase separation. This allows the recovery of high-molecular-weight DNA, which is particularly useful for applications such as long-read sequencing and genomic studies requiring intact DNA molecules (Liu et al., 2022).
Scalable: The protocol can be easily scaled for large-volume samples, including extractions from hundreds of milliliters of culture or environmental samples. Unlike column-based purification systems that are limited by binding capacity, this method maintains efficiency even when processing large sample volumes (Van der Merwe, 2019).
Limitations of the Phenol‑Chloroform Method of DNA Extraction
Chemical hazards: The method requires the use of phenol and chloroform, which are toxic, corrosive, and hazardous chemicals. Phenol can cause severe chemical burns, while chloroform exposure can lead to toxicity affecting the liver and other organs. Therefore, all procedures must be conducted inside a certified chemical fume hood, with strict adherence to laboratory safety practices and proper waste disposal protocols (Green & Sambrook, 2017).
Labor-intensive: The phenol–chloroform extraction procedure involves multiple manual steps, including repeated mixing, centrifugation, and phase separation. These steps increase hands-on processing time and manual handling, making the method slower compared with modern commercial DNA extraction kits (Liu et al., 2022).
Phenol carry-over: If residual phenol remains in the aqueous DNA phase, it can interfere with downstream enzymatic reactions, such as PCR amplification, restriction enzyme digestion, and other molecular biology assays. Proper washing steps with chloroform and careful phase separation are therefore necessary to ensure high DNA purity (Green & Sambrook, 2017).
Limited throughput: Because the method is time-consuming and requires extensive manual handling, it is not well suited for high-throughput laboratories processing large numbers of samples. In such cases, automated extraction platforms or column-based purification systems are generally preferred for improved efficiency, reproducibility, and laboratory safety (Liu et al., 2022).
Conclusion
The Phenol-Chloroform Method of DNA Extraction continues to be a reliable, flexible, and cost-effective technique for isolating high-quality DNA from a wide variety of biological sources, including cells, tissues, environmental samples, and microorganisms.
When reagent ratios are properly optimized, phase separation is carried out carefully, and washing steps are performed thoroughly, the method consistently produces high-purity DNA suitable for demanding molecular biology applications.
The DNA obtained through this technique is often appropriate for advanced molecular procedures, including sequencing, cloning, restriction enzyme analysis, and other downstream genomic analyses that require intact and uncontaminated DNA.
Although the procedure involves the use of hazardous chemicals such as phenol and chloroform, which require strict laboratory safety precautions and proper handling, the method remains widely used due to its effectiveness and reliability.
Modern adaptations of the technique, including magnetic-bead-based DNA capture systems and CTAB (cetyltrimethylammonium bromide) pre-treatment for complex samples, have improved the efficiency of the method and expanded its usefulness for samples containing inhibitors, polysaccharides, or other contaminants.
These improvements have made the phenol-chloroform extraction approach more adaptable for challenging sample types, including plant tissues, environmental samples, and inhibitor-rich biological materials.
Despite the widespread availability and convenience of commercial DNA extraction kits, this classical extraction method still retains significant value for laboratories that require high-purity, high-integrity DNA while maintaining low operational costs (Green & Sambrook, 2017; Liu et al., 2022; Van der Merwe, 2019).
References
A. W. Liu, A. Villar-Briones, N. M. Luscombe, & C. Plessy (2022). Automated phenol–chloroform extraction of high-molecular-weight genomic DNA for long-read single-molecule sequencing. bioRxiv. https://doi.org/10.1101/2022.01.26.477939
O. Reina (2025, June 5). Top 10 tips for phenol–chloroform extractions and ethanol precipitations. Bitesize Bio. https://bitesizebio.com
S. Van der Merwe (2019). DNA extraction from water and soil using the 50-50-50 buffer–chloroform/phenol method. protocols.io. https://doi.org/10.17504/protocols.io.8yphxvn
D. N. Miller, J. E. Bryant, E. L. Madsen, & W. C. Ghiorse (1999). Evaluation and optimization of DNA extraction and purification methods for soil and sediment samples. Applied and Environmental Microbiology, 65(11), 4715–4724.
Michael R. Green & Joseph Sambrook (2017). Isolation of high-molecular-weight DNA using organic solvents. Cold Spring Harbor Protocols, 2017(4), pdb.top093450. https://doi.org/10.1101/pdb.top093450
T. A. Brown (2020). Gene Cloning and DNA Analysis: An Introduction (8th ed.). Wiley-Blackwell.
Kathmandu University (2025). Phenol–chloroform extraction manual for human urine samples. Unpublished laboratory protocol.
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