Cetyltrimethylammonium Bromide (CTAB) (CAS 57-09-0) — Complete Guide to Properties and Applications

Category: Cationic Surfactant | Formula: C19H42BrN | MW: 364.45 g/mol

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What Is Cetyltrimethylammonium Bromide (CTAB)?

Cetyltrimethylammonium Bromide (CTAB) (CAS 57-09-0) is a quaternary ammonium cationic surfactant with the molecular formula C19H42BrN and molecular weight 364.45 g/mol ^[001]. The IUPAC name is hexadecyl(trimethyl)azanium bromide. CTAB consists of a long hydrophobic C16 alkyl tail and a hydrophilic trimethylammonium head group, giving it amphiphilic properties that drive micelle formation above its critical micelle concentration (CMC) ^[001].

CTAB is widely used as a structure-directing agent in nanomaterial synthesis, a cell lysis reagent in molecular biology, a phase-transfer catalyst, and an antiseptic/disinfectant in pharmaceutical formulations ^[004]. Its ability to form rod-shaped micelles makes it uniquely valuable in anisotropic nanoparticle synthesis.

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Physical and Chemical Properties

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How It Works

CTAB functions as a cationic surfactant through amphiphilic molecular architecture. The long C16 hydrocarbon tail provides hydrophobic character, while the trimethylammonium head group carries a permanent positive charge ^[004].

In aqueous solution below the CMC (~0.9 mM), CTAB exists as individual monomers. Above the CMC, molecules self-assemble into spherical micelles with hydrophobic tails inward and cationic heads outward. At higher concentrations (>20 wt%) or in the presence of counterions, CTAB forms rod-shaped micelles and hexagonal liquid crystalline phases — the basis for its structure-directing role in mesoporous material synthesis ^[004].

In gold nanorod synthesis, CTAB serves dual functions: (1) as a soft template that forms rod-like micelles directing anisotropic growth, and (2) as a stabilizing agent preventing nanoparticle aggregation through electrostatic repulsion of the cationic head groups ^[004]. The Br⁻ counterion also plays a critical role by selectively adsorbing onto specific crystal facets, promoting growth along the longitudinal axis.

In DNA extraction, CTAB's cationic head binds to the negatively charged phosphate backbone of DNA, forming an insoluble CTAB-DNA complex that precipitates from solution while polysaccharides and polyphenols remain soluble in the high-salt buffer ^[005].

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Key Applications

1. Gold Nanorod Synthesis: CTAB is the essential structure-directing agent in seed-mediated Au nanorod synthesis (Murphy/Jana method, 2001). Forms rod-shaped micelles that template anisotropic growth. Most-cited nanomaterial synthesis application. Typical: 0.1 M CTAB in aqueous solution with HAuCl4, AgNO3, and ascorbic acid. ^[004]

2. DNA/RNA Extraction from Plants: CTAB extraction buffer (2% CTAB, 1.4 M NaCl, 20 mM EDTA, 100 mM Tris pH 8.0) is the standard protocol for plant genomic DNA extraction. The cationic CTAB binds to DNA phosphate groups, causing selective precipitation while polysaccharides and polyphenols remain in solution. ^[005]

3. Mesoporous Material Template: Structure-directing agent for MCM-41 and SBA-15 mesoporous silica. Forms liquid crystal templates at concentrations >20 wt%. Enables 2–10 nm pore size control for catalysis and drug delivery applications. ^[004]

4. Phase-Transfer Catalysis: CTAB facilitates reactions between water-soluble and organic-soluble reactants by forming micelles that concentrate both reactants at the interface. Used in oxidation, reduction, and nucleophilic substitution reactions. ^[005]

5. Antimicrobial and Pharmaceutical: CTAB exhibits broad-spectrum antimicrobial activity against bacteria, fungi, and enveloped viruses. Used in throat lozenges, mouthwashes, and topical antiseptics at concentrations of 0.01–0.1%. ^[002]

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Representative Protocol: Gold Nanorod Synthesis via Seed-Mediated Growth

Objective: Synthesize gold nanorods with tunable aspect ratios using CTAB as structure-directing agent.

Materials:

- CTAB (CAS 57-09-0), ≥99% purity: 7.304 g (20 mmol) ^[002]

- Hydrogen tetrachloroaurate(III) trihydrate (HAuCl4·3H2O): 0.079 g (0.20 mmol)

- Silver nitrate (AgNO3): 0.034 g (0.20 mmol)

- L-Ascorbic acid: 0.035 g (0.20 mmol)

- Sodium borohydride (NaBH4): 0.006 g (0.16 mmol)

- Deionized water: 200 mL total

Procedure:

1. Seed solution: Dissolve CTAB (3.644 g, 10 mmol) in 100 mL water at 30 °C. Add HAuCl4 (0.025 g, 0.063 mmol). Stir 2 min. Add ice-cold NaBH4 (0.006 g in 1 mL water) rapidly. Stir vigorously 2 min. Solution turns brownish-yellow. Let stand 2 h before use. ^[004]

2. Growth solution: Dissolve CTAB (3.660 g, 10 mmol) in 100 mL water at 30 °C. Add HAuCl4 (0.054 g, 0.137 mmol), then AgNO3 (0.017 g, 0.10 mmol). Mix gently.

3. Add ascorbic acid (0.035 g, 0.20 mmol). Solution becomes colorless (Au³⁺ reduced to Au⁺).

4. Add 0.24 mL of seed solution. Mix gently and leave undisturbed at 27 °C for 12–24 h.

5. Nanorods form with longitudinal surface plasmon resonance (LSPR) at 650–850 nm depending on AgNO3 concentration.

Troubleshooting:

- Spherical particles instead of rods: CTAB concentration too low, or temperature too high. Maintain 25–30 °C.

- Poor yield: Ascorbic acid degraded — prepare fresh.

- Aggregation: Insufficient CTAB stabilization. Increase CTAB to 0.12 M.

Yield: Typically 80–95% based on gold precursor.

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Handling and Storage

- GHS Hazard: H302: Harmful if swallowed [97% of ECHA notifications]; H315: Causes skin irritation [45.6%]; H318: Causes serious eye damage [91.7%]; H335: May cause respiratory irritation [38.9%]; H373: May cause damage to organs through prolonged or repeated exposure [34.9%]; H400: Very toxic to aquatic life [95%]; H410: Very toxic to aquatic life with long lasting effects [26.1%] ^[001]

- Signal Word: Danger ^[001]

- Pictograms: GHS05 (corrosion, for H318), GHS07 (exclamation mark, for H302/H315/H335/H373), GHS09 (environment, for H400/H410) ^[001]

> GHS verification note (2026-06-20): CTAB GHS classification verified against PubChem CID 5974 ECHA C&L Inventory (823 notifications). Original entry incorrectly assigned GHS06 (skull) for H302 — H302 (Acute Tox. 4) uses GHS07, not GHS06. Added H335 (respiratory irritation, 38.9%) and H400 (aquatic acute toxicity, 95%) which were omitted in the original. H410 is present at 26.1% (not 100% as some suppliers may indicate). ^[001]

- Storage: Store at 2–8 °C in a tightly closed container. Protect from moisture (hygroscopic). CTAB is stable under normal conditions but decomposes above ~237 °C. ^[002]

- PPE: Nitrile gloves, safety goggles with side shields, lab coat, and closed-toe shoes. Use respiratory protection if handling large quantities or if dust is generated. Work in a well-ventilated fume hood. ^[002]

Always consult the Safety Data Sheet (SDS) from your supplier before handling. SDS documents are lot-specific — different purity grades may have different hazard classifications. Emergency procedures: in case of skin contact, wash immediately with soap and water for at least 15 minutes. For eye contact, rinse cautiously with water for several minutes and remove contact lenses if present. If swallowed, rinse mouth and seek medical attention immediately. Never discharge CTAB into drains or waterways — H400/H410 aquatic toxicity.

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Regulatory & Compliance

Chemical Inventories: CTAB (CAS 57-09-0) is listed on major chemical inventories including TSCA (United States), EINECS/EC 200-311-3 (EU), ENCS (Japan), IECSC (China), KECL (Korea), and AICS (Australia) ^[001].

GHS Classification: Harmonized across jurisdictions per ECHA C&L Inventory data (823 notifications). National implementations (EU CLP, US OSHA HazCom 2012, China GB 30000) may have additional requirements ^[001].

Environmental Regulations: CTAB is classified as very toxic to aquatic life (H400/H410). Discharge into waterways is prohibited in most jurisdictions. Wastewater containing CTAB must be treated before release. EU REACH registration required for >1 ton/year ^[001].

Transport Information: Not classified as dangerous goods for transport in most quantities (verify with supplier for bulk shipments). ^[002]

Export Control: Standard research and industrial chemical — no specific export controls known. ^[004]

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Frequently Asked Questions

Why is CTAB essential for gold nanorod synthesis but not for spherical nanoparticles?

CTAB forms rod-shaped micelles above its second critical micelle concentration in the presence of appropriate counterions. These micelles act as a soft template that constrains gold crystal growth to one dimension. Additionally, CTAB and Br⁻ ions selectively adsorb onto the {100} facets of growing gold crystals, promoting growth along the [110] axis. Spherical gold nanoparticles can be synthesized with citrate (no directional template), but anisotropic rods require CTAB's unique micellar morphology ^[004].

What is the difference between CTAB and SDS for DNA extraction?

CTAB is a cationic surfactant that binds to DNA through electrostatic interaction with the negatively charged phosphate backbone, causing selective precipitation in high-salt conditions. SDS is an anionic surfactant that lyses cells by disrupting membranes but does not precipitate DNA selectively. CTAB extraction is preferred for plant tissues rich in polysaccharides and polyphenols because CTAB-DNA precipitation leaves these contaminants in solution, whereas SDS-based methods require additional purification steps ^[005].

Can CTAB be substituted with other cetyltrimethylammonium salts?

CTAB (bromide salt) is the most commonly used form. CTAC (chloride salt) can be substituted in some applications but produces different micellar morphologies and may yield shorter nanorods in gold synthesis. The counterion (Br⁻ vs Cl⁻) affects micelle curvature and crystal facet binding. For DNA extraction, either salt works, but published protocols overwhelmingly specify CTAB ^[004].

How do I safely dispose of CTAB waste?

CTAB is highly toxic to aquatic life (H400/H410). Never pour down the drain. Collect all CTAB-containing waste (solutions, solids, contaminated PPE) in designated hazardous waste containers. Neutralize with activated carbon if permitted by local regulations. For large quantities, consult a licensed hazardous waste disposal contractor. Include CTAB waste in your institution's chemical hygiene plan ^[002].

What concentration of CTAB is needed for micelle formation?

The critical micelle concentration (CMC) of CTAB in pure water at 25 °C is approximately 0.9 mM (~0.03 wt%). Above this concentration, spherical micelles form. At concentrations >20 wt% or in the presence of salts, rod-shaped micelles and liquid crystalline phases appear. For gold nanorod synthesis, typical CTAB concentrations are 0.05–0.1 M (well above CMC). For DNA extraction, 2% (~55 mM) is standard ^[004].

Is CTAB safe for use in pharmaceutical products?

CTAB is approved for use in topical antiseptics, throat lozenges, and mouthwashes at concentrations up to 0.1%. However, it is not safe for ingestion at higher concentrations (H302) and causes serious eye damage (H318). Pharmaceutical formulations must comply with regional pharmacopeia limits. CTAB should not be used in parenteral or ophthalmic preparations due to cytotoxicity concerns ^[002].

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Where to Buy

Cetyltrimethylammonium Bromide (CTAB) (CAS 57-09-0) is not currently listed in the CoreyChem catalog. Contact [email protected] for sourcing assistance. ^[003]

Our sourcing team can assist with procurement from qualified manufacturers worldwide. Please provide the CAS number, required quantity, and desired purity when submitting your inquiry for the fastest response.

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