2-Phenoxyethanol Pharma Grade API (CAS 122-99-6; C₈H₁₀O₂; relative molecular mass 138.16 g/mol) is specified as a clear, colourless oily liquid for use in oral and injectable pharmaceutical manufacturing. The term “API grade” in this context denotes manufacture and release under active pharmaceutical ingredient quality systems; in finished-product dossiers the material is normally classified as an antimicrobial preservative rather than a therapeutic active. The grade is controlled against Ph. Eur. 0788 and released with a certificate of analysis covering assay by gas chromatography, water by Karl Fischer titration, residue on evaporation, sulfated ash, and related substances including free phenol. Industrial phenoxyethanol with the same CAS registry number is not a direct substitute because it may carry uncontrolled colour bodies, peroxides, and phenol-related impurities and lacks cGMP release documentation. The pharma-grade product is supplied in sealed stainless-steel drums or glass bottles under nitrogen, with batch-specific documentation suitable for injectable manufacture when endotoxin and microbial limits are ordered separately.

What Distinguishes a Pharma-Grade Phenoxyethanol Specification from Industrial Blends?

The specification difference is concentrated in impurity limits and microbiological burden rather than in the principal GC assay value. Pharma-grade release requires an assay in the range 99.0–100.5%, water ≤0.5%, and residue on evaporation ≤0.1%. The related-substances section of Ph. Eur. 0788 controls chromatographic impurities; free phenol is typically limited to ≤0.10% because phenol is a local irritant and can generate colour on storage. Technical-grade material is frequently supplied with a minimum assay of 95.0% and no related-substance certificate. When parenteral manufacture is intended, the decisive gap is bacterial endotoxin testing: the compendial monograph does not impose a universal endotoxin limit for every use, so the limit is defined by the product-specific calculation and verified by Ph. Eur. 2.6.14 or USP <85> when requested. A release documentation comparison is shown below.

At 20°C the material has a density of 1.102 g/cm³, a boiling point of 245°C, a flash point of approximately 121°C, and a water solubility of approximately 26 g/L. It is miscible with ethanol, acetone, and glycerol but only sparingly soluble in water. This solubility profile produces a clear processing constraint: direct addition of undiluted 2-phenoxyethanol to an aqueous granulation fluid may form oil-rich droplets that separate from the aqueous phase. In a top-spray fluid-bed granulator fitted with a 0.8 mm two-fluid nozzle at atomizing air pressure of 1.5–2.5 bar, the preservative is therefore incorporated as a pre-mix with the binder solution. The solvent system is adjusted with 10–30% v/v ethanol to maintain a single-phase liquid. Binder solution viscosity is maintained below 150 mPa·s at 25°C to support reproducible droplet formation; when the solution separates, the spray system can show pressure fluctuation and non-uniform preservative distribution in the dried granule. In production-scale trials, refractive index measurements of the binder solution are used as an in-process check for phase separation because the refractive index does not detect microbiological efficacy but does indicate changes in co-solvent composition.

Liquid-Phase Dosing in High-Shear Granulation and Capsule Fill Formulations

In a high-shear wet granulation process with a main impeller speed of 250–500 rpm and a chopper speed of 1500–2500 rpm, 2-phenoxyethanol is added as part of the binder solution, not as a dry powder component. It contributes no measurable dry granule tensile strength in microcrystalline cellulose–lactose formulations; its function is preservation of the aqueous phase during wet massing and drying. A typical concentration in the granulating liquid is 0.5–1.0% w/w. When expressed on dry granule mass, the resulting content is often below 0.1% w/w; therefore, preservation in the granule cannot be extrapolated to a high-water-activity reconstituted suspension. Finished oral liquids and suspensions must still be validated by antimicrobial effectiveness testing per USP <51> or Ph. Eur. 5.1.3. On a twin-screw continuous granulation line with a 25:1 length-to-diameter ratio and three kneading zones, the liquid feed is injected through a side-filling port. If the phenoxyethanol fraction exceeds 1.2% w/w in the water-rich phase, partial phase separation can produce a pump pressure oscillation greater than ±0.2 bar and uneven distribution in the granule. This was corrected in scale-up by reducing the liquid-to-solid ratio from 0.25 to 0.20 or by adding 15% v/v ethanol to the feed.

When the preservative is applied in tablet film coating rather than in the granulation fluid, the coating suspension is prepared at 10–15% w/w total solids and sprayed in a perforated pan coater with inlet air temperature 55–65°C and exhaust air temperature 38–45°C. 2-Phenoxyethanol at 0.5% w/w of the coating suspension is soluble in the aqueous alcohol carrier and does not alter the minimum film-forming temperature of a hydroxypropyl methylcellulose–polyethylene glycol coating system. Because the coating is applied to a low-water-activity tablet core, the antimicrobial function is relevant only for the coating liquid during processing; the dried film does not provide meaningful preservation in the tablet core.

For liquid-filled hard capsules, the material is added to the fill vehicle at 0.5–1.0% w/w. Polyethylene glycol 400 and propylene glycol provide single-phase vehicles; medium-chain triglycerides are miscible but can reduce preservative availability because 2-phenoxyethanol partitions preferentially into the lipid phase. When the fill vehicle contains glycerol, the capsule filling machine hopper is usually heated to 30–35°C to maintain fill weight uniformity; the vehicle can exceed 500 mPa·s at 20°C. Gelatin capsule shells require an anhydrous fill: residual water in the fill above 3.0% may soften the shell and cause deformation at 40°C/75% RH. Published stability data for this specific liquid-filled configuration is limited; internal stress studies at 25°C/60% RH and 40°C/75% RH are therefore used before commercial batch release.

When the Target Profile Is an Injectable or Oral Liquid Requiring Non-Paraben Preservation

For oral liquids, phenoxyethanol is used at 0.5–1.0% v/v and is validated by challenge testing under USP <51> or Ph. Eur. 5.1.3 with the five specified organisms. Its gram-negative spectrum is narrower than that of chlorobutanol against Pseudomonas aeruginosa when used alone at 0.5%; formulators often combine it with a chelating agent or reduce product pH to meet the acceptance criterion. For injectable products, the concentration is lower and product-specific. Phenoxyethanol is used in selected multi-dose vaccine presentations at a fixed per-dose amount; a 0.5 mL dose may contain 2.5 mg phenoxyethanol. This level is product-specific and is not a universal monograph limit. Batches intended for parenteral manufacture require bacterial endotoxin testing per Ph. Eur. 2.6.14 or USP <85> and filtration through a 0.22 µm sterilizing-grade membrane before storage or filling. The material is compatible with stainless steel, polytetrafluoroethylene, and polypropylene contact surfaces; sorption into rubber closures can occur if the closure formulation contains high levels of unsaturated elastomers, and chlorobutyl or bromobutyl closures are preferred for multi-dose containers.

Compared with benzyl alcohol, 2-phenoxyethanol has a higher boiling point (245°C vs 205°C) and lower volatility, which reduces evaporative loss during aqueous processing and filling. Benzyl alcohol carries a documented gasping-syndrome restriction in neonates; phenoxyethanol is used in vaccines but is not free of all limitations because it is metabolized by alcohol dehydrogenase and aldehyde dehydrogenase to phenoxyacetic acid, requiring product-specific paediatric safety review. Compared with methylparaben and propylparaben, the ether linkage of phenoxyethanol avoids the ester hydrolysis that generates p-hydroxybenzoic acid and methanol in aqueous formulations at elevated temperature; the degradation product profile is therefore monitored by a single related-substances method rather than by separate ester hydrolysis markers. Compared with chlorobutanol, phenoxyethanol does not require a low pH for activity and is less volatile, but chlorobutanol generally has stronger activity against Pseudomonas aeruginosa at equivalent concentrations. Selection is therefore made on the basis of the finished product’s pH, packaging, paediatric exposure, and the required preservative challenge profiles.

Pharmacopoeial release testing under Ph. Eur. 0788 does not replace storage and cleaning controls. Because the material can form peroxides after prolonged air exposure, it is packed under nitrogen and assigned a retest interval of 24 months. After opening, storage above 30°C increases peroxide development and can generate phenol-related odour. Incompatibilities include strong bases, strong oxidizers, and plastic packaging that permits migration into the closure or tubing; high-density polyethylene containers are generally acceptable for short-term oral liquid storage, but long-term injectable contact surfaces are qualified by extractables testing. For cleaning of stainless-steel mixing vessels, cold water alone is insufficient because the aqueous solubility is approximately 26 g/L. A solvent-based pre-rinse with ethanol or a 0.5% polysorbate 20 solution is used to achieve a visual-clean surface; the HPLC swab limit of quantitation is typically set at 1–5 µg/mL. These operational controls are not specified in the pharmacopoeial monograph but are necessary to prevent preservative loss, cross-contamination, and peroxide formation during pharmaceutical manufacture.