Bromothymol Blue-Phenol Red Indicator - BioReagent

Cat. No.: B1528818

GRADE & PURITY BioReagent

Storage

Room temperature

Shipped In

Normal

Overview

This product is a mixed acid-base indicator prepared by combining Bromothymol Blue and Phenol Red in an optimized ratio. Bromothymol Blue has a transition range of pH 6.0 (yellow) to 7.6 (blue); Phenol Red has a transition range of pH 6.8 (yellow) to 8.4 (red). When combined, the indicator exhibits a continuous and sensitive color response to pH changes in the neutral to weakly alkaline range: pH < 6.0 appears yellow; pH 6.0–7.6 transitions from yellow to yellowish-green to green; pH 7.6–8.4 shifts to purplish-red; pH > 8.4 appears red. This indicator is suitable for rapid visual pH assessment of cell culture media and buffer systems, pH monitoring of microbial culture media, titration indicators in biochemical experiments, and educational laboratory demonstrations. It can also be used for simple pH screening of bicarbonate buffer systems (e.g., cell culture-related systems). Note: This product is intended for visual indication only and cannot replace precise pH meter measurements. Store protected from light. Do not use if discoloration, turbidity, or precipitation occurs. Avoid contact with skin and eyes. For research use only. Not for clinical diagnosis.

Specifications

Specifications & Purity

BioReagent

Storage

Room temperature

Shipped In

Normal

Grade

BioReagent

Product Line

biological_products

Application Protocols

The following are general, literature-based protocols for using a bromothymol blue–phenol red mixed indicator. They are provided as practical guidance and are not item specifications.

1. Aqueous-basic stock (0.1% w/v)

• Add 100 mg indicator mixture to a 100 mL volumetric flask.
• Add ~80 mL DI water containing 1–2 mM NaOH; swirl to dissolve.
• Bring to volume with the same solvent. Filter (0.22 µm) into an amber bottle. Store at room temperature, protected from light.
• Working use: Add 100–500 µL per liter of buffer to achieve 10–50 mg/L.

2. Ethanolic stock (0.04% w/v)

• Dissolve 40 mg in 100 mL absolute ethanol. Mix until homogeneous.
• Working use: Add 0.5–2.0 mL per liter of aqueous solution; verify that final ethanol content is acceptable for your assay.

3. Color calibration in buffers

• Prepare a series of buffer standards (e.g., pH 6.4–8.4 at 0.2 pH increments).
• Add indicator to 20 mg/L. Record visual color and measure absorbance at representative λmax (e.g., ~430/560 nm for phenol red; ~427/615 nm for BTB; literature values).
• Build a calibration curve of Abase/Aacid vs pH for your matrix to enable ratiometric estimation.

4. Cell-culture media checks (qualitative)

• Add minimal indicator (e.g., 5–10 mg/L) to bicarbonate/CO2-buffered media for training or QC simulations; equilibrate at target CO2 and verify expected neutral color. Avoid in hormone-sensitive studies due to phenol red’s weak estrogenic activity (literature).

Biological Roles

Applicability

• This product is a laboratory indicator mixture and is not intended to exert biological activity. The following notes describe general interactions of sulfonephthalein indicators in biological contexts (literature), not item-specific claims.

General considerations (literature)

• Phenol Red has been reported to display weak estrogenic activity at certain concentrations in cell culture, potentially influencing hormone-responsive assays. Many serum-free or hormone-sensitive protocols therefore specify phenol red–free media.
• Both dyes can interact nonspecifically with proteins and membranes via hydrophobic and ionic interactions; at typical indicator concentrations, such effects are often minor but assay-dependent.
• Indicators may contribute to background absorbance or fluorescence in optical readouts (e.g., 430–620 nm window). Spectral overlap with assay chromophores/fluorophores should be evaluated.
• Acid–base equilibrium of the dyes can be influenced by ionic strength, temperature, and cosolvents, slightly shifting apparent pKa in complex biological matrices.

Practical guidance

• Validate indicator concentration for each biological assay to avoid interference.
• For live-cell applications, confirm CO2/bicarbonate buffering compatibility; dissolved CO2 will impact BTB color via carbonic acid formation.
• When studying endocrine signaling, consider dye-free controls or phenol red–free conditions.

Research use only: As stated in the Product Data, this product is for research use only and not for human or animal therapeutic or diagnostic use.

Buffer Applications

Relevance

• Highly applicable. The bromothymol blue–phenol red mixture offers an extended visual transition covering approximately pH 6.5–8.0 (literature), matching common biological buffers.

Use with common buffers (practical guidance)

• Phosphate buffer (pH 6.0–8.0): Enables quick endpoint visualization during acid/base titration to physiological pH.
• HEPES (pH 6.8–8.2) and MOPS (pH 6.5–7.9): Visual cue during initial preparation; final pH verification should be by calibrated pH meter.
• Tris (pH 7.0–9.0): Phenol red component remains responsive into mildly basic range aiding fine adjustments above neutrality.
• Bicarbonate/CO2 systems: BTB sensitively reflects dissolved CO2 changes, useful for equilibrating media under 5% CO2.

Working concentrations (literature)

• Typical indicator use: 2–50 mg/L total dye mixture. Start at ~10 mg/L and adjust for visibility and spectral methods.

Procedural hints

• Add indicator near the final stages of titration to avoid overshooting due to color bias.
• Record the color at known pH values in your buffer matrix to create a local color chart (lighting-dependent).
• For spectrophotometric pH tracking, measure Aacid and Abase wavelengths for each component and construct an empirical calibration curve.

Compatibility

• Most buffers and salts are compatible; avoid strong oxidants/reductants that can bleach dyes. Filter sterilize indicator-containing buffers when sterility is required.

Green Alternatives

Context

• Indicators are typically used in very low concentrations, limiting environmental burden. Nevertheless, greener practices focus on solvent choice, stock concentration, and waste minimization.

Greener practices for this indicator mixture (general guidance)

• Prefer aqueous stocks adjusted with minimal base over alcoholic or DMSO stocks when compatible with the assay.
• Prepare concentrated stocks to minimize packaging and transport footprint, but avoid over-concentration that leads to precipitation in aqueous matrices.
• Use sterile filtration and small aliquots to extend shelf life and reduce discarded, expired solutions.

Comparison of preparation options (literature-based)

• Aqueous (slightly basic) stock:
  • Pros: No VOC emissions; highest biocompatibility; easy disposal when neutralized.
  • Cons: Potential microbial growth; may require NaOH/KOH; somewhat shorter shelf life without preservatives.
• Ethanol stock:
  • Pros: Rapid dissolution; good stability; easy handling.
  • Cons: VOC emissions; flammability; possible effects on sensitive bioassays.
• DMSO stock:
  • Pros: Excellent solubility; allows very small dosing volumes.
  • Cons: DMSO disposal considerations; can affect membrane permeability/enzymes.

Alternative indicators (use-case driven; literature)

• HEPES/Good’s buffers with built-in pH control (no indicator required) reduce the need for dyes in some workflows.
• Single-component indicators (e.g., bromothymol blue alone) may suffice and slightly reduce chemical inventory if a narrower range is acceptable.

Note: Waste streams containing dyes should be collected per local regulations; activated carbon can aid decolorization in some treatment schemes.

Pharmaceutical Uses

Scope

• No medical or clinical claims. This indicator mixture is intended for research and laboratory applications. The points below describe general, non-therapeutic, formulation-adjacent uses (literature) and do not imply pharmacopeial status for this specific item.

Potential roles in pharmaceutical/bioprocess laboratories (general)

• In-process control (IPC): Visual pH tracking during development-scale buffer preparation or cleaning validation where near-neutral endpoints are specified.
• Assay development: Colorimetric readouts in compendial or in-house methods requiring pH verification without a meter (e.g., quick checks of carbonate-based mobile phases during method scouting).
• Device/packaging studies: Qualitative CO2 ingress/egress visualization in packaging headspace experiments using BTB sensitivity to carbonic acid formation.

Regulatory and compliance notes

• Pharmacopeial listings for specific indicators apply to defined monographs and purity criteria. This product’s pharmacopeial status, if any, is Not specified for this item; refer to CoA/Spec Sheet.
• For GMP use, qualification requires full specification, traceability, and change control; this catalog item is designated BioReagent for research use.

Practical considerations

• Use low concentrations to avoid interference with UV detection in analytical methods.
• Document indicator lot, concentration, and solvent system in method records for reproducibility.

Physical Properties

Item-specific physical properties

• Appearance: Not specified for this item; refer to CoA/Spec Sheet.
• Molecular formula, molecular weight, density, refractive index, melting point, boiling point, water content, UV cutoff: Not specified for this item; refer to CoA/Spec Sheet.

General/literature properties for the components (for context; not item specifications)

• Acid–base behavior:
  • Bromothymol Blue: pKa ~7.1 (25 °C); color transition yellow (HIn) to blue (In–) across pH 6.0–7.6.
  • Phenol Red: pKa ~7.9 (25 °C); color transition yellow (HIn) to red (In–) across pH 6.8–8.2.
• Spectral features (aqueous, literature):
  • BTB λmax typically ~427 nm (acid form) and ~615 nm (base form).
  • PR λmax typically ~433 nm (acid form) and ~558 nm (base form).
• Solubility tendencies:
  • Both dyes are sparingly soluble in neutral water as free acids, but readily soluble in ethanol and in aqueous media when converted to their sodium/potassium salts or when a small amount of base is added (literature).
• Stability considerations (literature):
  • Indicator solutions are generally stable for weeks at room temperature when protected from strong light and microbial contamination.
  • Aqueous stocks may exhibit slow photobleaching; amber storage and biocide/filtration are commonly used.

Note: Because this is a formulated mixture, precise bulk physical parameters depend on the blend ratio and salt forms; consult the CoA/SDS for item-specific values.

Quality & Grades

Item-specific quality

• Grade/Purity: BioReagent (as provided). No additional specifications (e.g., dye content, heavy metals, UV cutoff, stabilizers) are provided in the Product Data. For exact limits and acceptance criteria, see the CoA/Spec Sheet.

What BioReagent typically signifies (general guidance)

• Intended for biochemical and life-science research workflows where lot-to-lot consistency, low bioburden, and controlled impurity profiles are important.
• Emphasis on consistent spectroscopic behavior (color transition pH, absorbance profile) and minimized interfering contaminants for enzymatic assays and cell-culture–adjacent applications.

Considerations specific to indicator mixtures

• Blend homogeneity: Mixed indicators must be uniformly blended to ensure reproducible transition color and sensitivity; reputable BioReagent sourcing supports this requirement.
• Salt form and hydration state: The apparent potency (w/w vs w/v) and solubility depend on the acid vs sodium salt forms of each dye. Confirm with the CoA for accurate solution preparation.
• Background absorbance/fluorescence: For spectrophotometric or imaging assays, verify baseline absorbance of buffers/solvents without indicator to account for matrix effects.

Quality control suggestions (user-side checks)

• Record a reference spectrum of your working solution; verify λmax and A(λ) ratios against literature/your method.
• Titrate a standard buffer (e.g., 6.0–8.5) to confirm the expected color change window before use in critical assays.

Reaction & Applications

Scope of use (laboratory; research only)

• Mixed neutral-range pH indicator for visual or spectrophotometric monitoring across approximately pH 6.5–8.0, leveraging overlapping transitions of bromothymol blue (BTB) and phenol red (PR) (literature).

Representative applications (literature)

• Buffer preparation and verification: Rapid visual check during titration of phosphate, HEPES, Tris, MOPS, or bicarbonate buffers near physiological pH.
• Enzyme assays: Monitoring reactions that generate/consume protons (e.g., ATP hydrolysis, dehydrogenase-coupled reactions with bicarbonate/CO2) by tracking color/absorbance shifts.
• Microbiology/bioprocess: Colorimetric readout of metabolic acidification/alkalinization in culture media; mixed indicator broadens readability around neutrality.
• Gas exchange/respirometry: BTB component is sensitive to dissolved CO2/bicarbonate equilibria (carbonic acid formation), enabling qualitative visualization in closed systems (literature practice).
• Teaching and QA/QC: Demonstrations of buffer capacity and acid–base equilibria; quick checks of rinse solutions and cleaning validation endpoints where near-neutral pH is targeted.

Practical tips

• Use low indicator concentrations to avoid perturbing ionic strength or introducing absorbance bias; verify that the indicator does not chelate metals or interfere with assay chromophores.
• Calibrate color with a pH meter in your matrix; proteins, salts, and solvents can shift apparent transition behavior.
• For spectrophotometry, select wavelengths where BTB and PR have well-separated acid/base λmax to enable ratiometric readouts.

Reaction Conditions

Context

• As a pH indicator mixture rather than a reactant, “reaction conditions” pertain to preparing and using the dye solution effectively. Values below are general literature guidance and not item specifications.

Typical working ranges

• pH sensitivity window: Approximately 6.5–8.0 overall, derived from BTB (6.0–7.6) and PR (6.8–8.2) transitions (literature).
• Concentration: 2–50 mg/L in the working solution; choose the lowest concentration that affords a clear visual/spectral response.

Stock solution preparation (examples; literature)

• Aqueous-basic stock: Dissolve the mixture to 0.1–1.0% (w/v) in water containing 1–10 mM NaOH or KOH; mix until homogeneous; optionally sterile filter (0.22 µm); store protected from light.
• Ethanolic stock: 0.04–0.5% (w/v) in absolute ethanol or 95% ethanol; mix thoroughly; protect from light; dilute into aqueous systems just before use.

Operating conditions

• Temperature: Ambient laboratory temperatures (15–30 °C) are typical. pKa values may shift slightly with temperature; re-verify color endpoints for non-ambient work.
• Ionic strength: High salt can modestly affect apparent transition; calibrate in the target matrix.
• Light: Minimize intense light exposure to reduce photobleaching; use amber glassware.

Expected performance (literature)

• Fast, reversible color change within seconds of pH adjustment in well-stirred solutions.
• Spectral monitoring at acid/base λmax pairs enables ratiometric pH estimation with good repeatability when calibrated.

Safety & Handling

Item-specific hazard information

• GHS classification, signal word, hazard statements (H-codes), pictograms: Not specified for this item; refer to SDS.

General safety guidance (literature/best practice; not a substitute for the SDS)

• Likely hazards: Dyes may cause eye/skin irritation and staining; dust may be irritating to respiratory tract. Avoid inhalation of powders, contact with eyes/skin, and ingestion.
• Personal protective equipment (PPE): Use lab coat, safety glasses or goggles, and appropriate disposable gloves (e.g., nitrile). Employ local exhaust ventilation when weighing powders.
• Handling tips:
  • Prepare solutions in a fume hood to minimize dust and aerosol exposure.
  • Use amber glass or foil wrap to limit photodegradation.
  • For aqueous stocks, reduce bioburden by sterile filtration (0.22 µm) where appropriate.
• Incompatibilities (general): Strong oxidizing agents may degrade organic dyes; strong acids/bases can irreversibly alter color if outside indicator stability range for prolonged times; avoid hypochlorite bleach contact (staining/oxidation).
• First aid overview: If on skin/eyes, rinse with water for several minutes; remove contaminated clothing. If inhaled, move to fresh air. If ingested, rinse mouth with water. Seek medical attention as needed. Always follow institutional EHS procedures.
• Spill response: Avoid raising dust; collect with damp disposable towels or HEPA vacuum. Dispose of waste according to local regulations.

Always consult the product-specific SDS for authoritative hazard, exposure limits, and disposal guidance.

Solvent Selection

Applicability

• As a pH indicator mixture, solvent selection focuses on preparing concentrated stocks that are stable, filterable, and compatible with the target assay matrix.

General solvent behavior (literature)

• Water: Limited solubility for free-acid forms; excellent solubility for sodium/potassium salts or with slight alkalinization (e.g., 1–10 mM NaOH). Preferred for biological compatibility.
• Ethanol/Isopropanol: Good solubility for both components; commonly used for concentrated stocks that are later diluted into aqueous systems. Consider final alcohol content in sensitive assays.
• DMSO: High solubility; useful for small-volume additions, but evaluate DMSO effects on cells/enzymes.

Polarity and miscibility

• Both dyes are polar aromatic sulfonephthaleins; their salts are water-miscible. Alcoholic and aqueous media are fully miscible with typical stock formulations.

Selection guidance

• Cell culture/biochemical assays: Prefer aqueous or minimally alcoholic stocks (e.g., aqueous with slight base) to reduce solvent artifacts.
• Titrimetry/teaching labs: Ethanol or water–ethanol mixtures provide rapid dissolution and long shelf life.
• Spectroscopy: Use high-purity water or alcohol; filter through 0.22 µm to remove particulates and obtain smooth baselines.

Small comparison (literature)

• Aqueous-basic stock: Maximal biological compatibility; may have shorter shelf life due to microbial growth—use sterile technique.
• Ethanolic stock: Longer shelf life and rapid wetting; watch for solvent effects in enzyme/cell assays.

Storage & Reconstitution

Item-specific conditions (from Product Data)

• Storage conditions: Room temperature.
• Shipped in: Normal.
• Additional item-specific details (stabilizers, shelf life, reconstitution solvent): Not specified for this item; refer to CoA/Spec Sheet.

General guidance (literature/practice)

• Light protection: Store powders and solutions in amber containers or protected from light to limit photobleaching.
• Moisture control: Keep container tightly closed to minimize moisture uptake and clumping. Desiccation is helpful for long-term powder storage.
• Reconstitution solvents: Use DI water with slight base (e.g., 1–10 mM NaOH/KOH) for aqueous stocks, or high-purity ethanol for alcoholic stocks, depending on application needs.
• Sterility: For bioassay use, sterile-filter aqueous solutions (0.22 µm) and consider aliquoting to reduce contamination risk.
• Freeze–thaw: Not typically required or recommended; store at room temperature per Product Data. If refrigeration is used for convenience, avoid repeated freeze–thaw of aqueous solutions.
• Shelf life (solutions): Prepare in small batches. Replace solutions that show precipitate, unexpected color, or spectral changes.

Research Use Note

• For research use only. Not for human or animal therapeutic or diagnostic use. Always consult the SDS and CoA for item-specific stability and handling information before first use.

Structure & Identity

Brief description: This product is a blended pH indicator consisting of bromothymol blue and phenol red, formulated for laboratory and life-science applications where a neutral-to-slightly-basic transition range is desired.

Item-specific identifiers (from Product Data)

• SKU: B1528818
• Product name: Bromothymol Blue-Phenol Red Indicator (mixture)
• Grade/Purity: BioReagent
• CAS, InChIKey, SMILES, molecular formula, molecular weight: Not specified for this item; refer to CoA/Spec Sheet.

Component identities (literature; for context only, not item specifications)

• Bromothymol Blue (BTB): sulfonephthalein dye; typical pKa ≈ 7.1; color change yellow (acid) → blue (base) with a green midpoint; often cited transition range 6.0–7.6.
• Phenol Red (PR): sulfonephthalein dye; typical pKa ≈ 7.9; color change yellow (acid) → red (base); often cited transition range 6.8–8.2.

Structural features (literature)

• Both components are sulfonephthalein triphenylmethane-type dyes containing a spiro-lactone/quinonoid equilibrium that shifts with pH.
• Extended aromatic systems with phenolic substituents and sulfonate/sulfone functionality enable strong visible absorbance and water compatibility (as salts) under basic/neutral conditions.

2D structure description (literature)

• Central triarylmethane framework fused to a cyclic sulfone (sulfonephthalein core). Protonation state controls ring opening/closing and conjugation length, producing distinct colors across the transition region.

Synthetic Utility

Relevance

• While not a synthetic building block, this mixed indicator is useful for monitoring processes and conditions in chemical synthesis.

Use-cases in synthetic and analytical chemistry (literature)

• Acid/base reaction monitoring: Visual cue for completion or endpoint in neutralization and salt formation near physiological pH.
• Workup optimization: Quick assessment of aqueous layer pH during extractions or washes, particularly when targeting neutrality to protect base/acid-labile functionalities.
• Enzymatic catalysis and biocatalysis: Non-invasive pH readout in aqueous biotransformations and whole-cell catalysis; the combined transition of BTB+PR improves sensitivity across 6.5–8.0.
• Gas-evolving reactions: Qualitative detection of CO2 evolution/absorption in bicarbonate-buffered media.

Method development tips

• Establish a matrix-specific calibration curve if using spectrophotometrically; ionic strength and cosolvents can shift apparent transition points.
• Maintain low indicator levels (<0.01% w/v) to minimize potential interactions with catalysts, metals, or organics.
• Avoid strong oxidants (e.g., permanganate, hypochlorite) and strong nucleophiles that may irreversibly alter dye chromophores, leading to false color readings.

Complementary tools

• Combine with electrode-based pH measurement for quantitative control; use the indicator as a rapid screening tool to conserve electrode life and reduce cleaning cycles.

Target Specificity

Not applicable. This product is a chemical indicator mixture, not a biological affinity reagent. No antigen, epitope, clone, isotype, or species reactivity applies. Item-specific immunochemical targeting data are not provided in the Product Data.