Phenol PH is supplied as a pre-equilibrated biphasic reagent in which the organic phase has been saturated with a defined aqueous buffer before packaging. The product is specified for nucleic acid partitioning workflows in molecular biology production facilities, clinical nucleic acid extraction platforms, and research laboratories that require high-molecular-weight DNA or selective RNA recovery. The designation PH refers to the controlled aqueous-phase pH after phase separation at 25 °C, not to the pH of the anhydrous phenol stock. Three model configurations are released: PH 4.5, PH 6.7, and PH 7.8. The phenol component carries CAS number 108-95-2 and is assayed at ≥ 99.5% by gas chromatography before buffer equilibration; acceptance criteria are aligned with ASTM D2439 for phenol. Each configuration includes 0.1% w/v 8-hydroxyquinoline as an oxidation inhibitor and is packaged under nitrogen in amber glass bottles. Compared with laboratory-prepared water-saturated phenol, the pre-equilibrated formulation reduces batch-to-batch pH drift and avoids manual titration of the organic phase. The product carries GHS hazard statements H301, H311, H314, and H331; handling requires a chemical fume hood, nitrile gloves, and eye protection.

Which Release Limits and Analytical Methods Govern the Three PH Configurations?

Representative release limits for the product line are listed in Table 1. The aqueous-phase pH is measured after 1:1 dilution with distilled water at 25 °C. Phenol assay is performed before buffer saturation because the buffer components interfere with direct gas chromatographic quantification of the organic phase. Nuclease activity release screening is not defined by a single ASTM method; the procedure uses gel electrophoresis after incubation of the reagent with nucleic acid substrates under defined conditions.

The PH 6.7 configuration is available for simultaneous recovery of DNA and RNA from viral transport media and cultured cells. Its release criteria follow the same phenol assay and nuclease limits as the PH 7.8 model, with the aqueous-phase pH controlled within 6.7 ± 0.2. This intermediate pH is selected where acidic phenol precipitation of genomic DNA is undesirable but where the extraction workflow must retain both nucleic acid classes for subsequent quantitative PCR or RT-PCR analysis.

In a stainless-steel rotor-stator homogenizer operating at 10,000 to 14,000 rpm, 1 volume of clarified cell lysate is combined with 1 volume of Phenol PH 7.8 and mixed for 30–60 s. The emulsion is transferred to a fixed-angle centrifuge and separated at 12,000 × g for 5 min at 4 °C. Under these conditions, double-stranded DNA accumulates in the upper aqueous phase while denatured protein and insoluble debris collect at the interphase. The lower phenol-rich phase retains hydrophobic peptides, lipids, and residual chloroform-extractable species. The aqueous phase is recovered, re-extracted with chloroform at a 1:1 volume ratio to remove dissolved phenol, and precipitated with 0.3 M sodium acetate (pH 5.2) plus 2 volumes of absolute ethanol at −20 °C. Typical purified genomic DNA in 10 mM Tris-HCl (pH 8.0) exhibits an A₂₆₀/A₂₈₀ ratio between 1.80 and 2.00 and an A₂₆₀/A₂₃₀ ratio above 2.0. The A₂₆₀/A₂₃₀ threshold is used as a release check for residual phenol and carbohydrate contamination.

During scale-up from 2 mL microcentrifuge tubes to 50 mL conical tubes in a liquid-handling workstation, pH drift at the aqueous-organic interface becomes a measurable process conflict. In larger vessels, the interfacial area-to-volume ratio decreases, and the time required for complete proton transfer between the equilibrated aqueous phase and the phenol phase increases. If the aqueous phase pH is measured immediately after vortexing, values may differ from the labeled setpoint by up to 0.3 pH units. The pH must be recorded after centrifugation and phase separation, because the clarified upper phase is the phase used for nucleic acid precipitation. In automated platforms, a 60 s rest period after mixing is used before centrifugation to permit buffer re-equilibration; shortening this rest period shifts the measured pH and changes DNA/RNA distribution.

When Phenol PH 7.8 Is Substituted for Acidic Phenol in RNA Extraction

Substitution of Phenol PH 4.5 for Phenol PH 7.8 changes nucleic acid distribution across the two liquid phases. At pH 4.5, partial protonation of the phosphate backbone lowers the aqueous solubility of DNA, and denatured double-stranded DNA collects at the interphase with protein. RNA remains in the upper aqueous phase under the same acidic conditions. At pH 7.8, both DNA and RNA exhibit ionized phosphate backbones and both remain in the aqueous phase. Therefore PH 4.5 is specified for selective RNA recovery, whereas PH 7.8 is specified for DNA extraction or total nucleic acid recovery followed by RNase treatment. If PH 7.8 is introduced into an acidic-phenol RNA protocol, genomic DNA carryover into the final nucleic acid pellet is expected; the recovered material requires DNase I digestion at 37 °C for 20 min in 10 mM Tris-HCl (pH 7.5), 2.5 mM MgCl₂, and 0.5 mM CaCl₂. Published data comparing the two configurations across complex tissue matrices are limited; spike-recovery testing with a reference nucleic acid is recommended before platform qualification.

Table 2 summarises the partition profile across the three configurations under identical centrifugation conditions. The interphase is defined as the visible precipitated layer between the upper aqueous phase and the lower phenol-rich phase after fixed-angle centrifugation at 12,000 × g for 5 min.

Storage, Oxidation, and Phase-Separation Limits

Phenol PH is stored at 2–8 °C in a sealed amber bottle. At ambient temperatures above 25 °C, the pre-equilibrated buffer layer can phase-separate from the phenol layer; brief vortexing restores saturation only when the bottle has remained closed and the water content has not evaporated. Exposure to atmospheric oxygen accelerates conversion of phenol to quinone species, particularly at pH values above 7.0. The 0.1% w/v 8-hydroxyquinoline in the formulation complexes trace iron and scavenges radical intermediates, producing a yellow-green coloration; it does not prevent oxidation indefinitely. A red or pink tint indicates accumulated oxidation products, and use of such material is avoided because quinones can introduce single-strand breaks in nucleic acids and crosslink protein. In high-throughput nucleic acid extraction facilities, opened bottles are aliquoted under nitrogen and stored at 2–8 °C for no more than 6 months. Freeze-thaw cycling is not recommended because buffer crystallisation disturbs the equilibrium water content of the organic phase, and subsequent pH drift at the aqueous-organic interface can exceed 0.2 pH units. Before use, the aqueous phase pH is verified after 1:1 dilution with distilled water at 25 °C by glass electrode measurement equivalent to ASTM E70.

In waste-handling operations, the product is incompatible with strong oxidizers, strong acids, and concentrated hydrogen peroxide. Mixing with chlorine bleach generates chlorinated phenols and heat. Waste disposal falls under the RCRA listed hazardous waste code U188 for phenol. Neutralisation with sodium hydroxide requires temperature control because the reaction exotherm can exceed 80 °C in concentrated systems.

The Distinction from Anhydrous Phenol and Phenol-Chloroform-Isoamyl Alcohol

Anhydrous phenol solid must be melted at 40–50 °C, equilibrated with buffer, and titrated to the required pH before use. Phenol PH removes those preparation steps because the organic phase is already saturated with buffer at the labeled pH. Phenol-chloroform-isoamyl alcohol (25:24:1 v/v/v) differs by the presence of chloroform and isoamyl alcohol; chloroform denatures proteins, increases the density of the lower phase, and removes residual phenol from the aqueous layer, while isoamyl alcohol reduces foaming. Phenol PH lacks chloroform, so a separate chloroform back-extraction is required when low A₂₆₀/A₂₃₀ ratios are specified. Acidic phenol-chloroform mixtures at pH 4.5 are used for selective RNA recovery; Phenol PH 7.8 cannot be directly substituted without altering the DNA/RNA partition profile. Compared with silica membrane columns, Phenol PH permits recovery of high-molecular-weight DNA above 50 kb, although the manual workflow is more hazardous and less amenable to automation. Published data comparing extraction yields between Phenol PH and laboratory-prepared phenol are limited across different tissue types; users are advised to qualify each matrix with a spike-recovery study using sheared salmon sperm DNA or an equivalent reference nucleic acid.

For extraction from formalin-fixed paraffin-embedded tissue, proteinase K digestion at 56 °C for 12–16 h precedes phenol extraction, and the aqueous-phase pH is rechecked after overnight digestion because buffering capacity can shift. The PH 7.8 configuration is selected for formalin-fixed DNA recovery when the target amplicon length exceeds 200 base pairs; for shorter fragments, silica-based purification may be preferred because phenol extraction generates longer DNA but lower yield below 100 base pairs in some matrices.