Phenol Red (CAS 143-74-8)

Executive summary: Phenol red (CAS 143-74-8) is a pH indicator dye widely used in cell culture media, diagnostic assays, and pharmaceutical research as a colorimetric pH sensor. This specialty chemical, available in ACS reagent grade, serves as a critical quality control standard for buffer validation and biological pH monitoring. Its application spans biotechnology, clinical diagnostics, and academic research laboratories.

Category Overview

Specialty chemicals encompass high-purity compounds designed for specific analytical, pharmaceutical, or industrial applications. Unlike commodity chemicals, these products require stringent quality specifications and are often subject to regulatory oversight from bodies such as the USP, EP, or FDA. Phenol red (CAS 143-74-8) exemplifies this category as a pH-sensitive dye with a transition range between pH 6.8 (yellow) and pH 8.2 (red), making it indispensable for visual and spectrophotometric pH determination in aqueous solutions.

1 product currently listed in this category (ACS reagent grade)

143-74-8 CAS registry number for Phenol red

6.8–8.2 pH transition range for colorimetric detection

The category plays a foundational role in the chemical supply chain, supporting quality control laboratories, pharmaceutical development teams, and academic researchers who require reproducible pH indicators for buffer preparation, cell viability assays, and endocrine-disrupting chemical studies.

Complete Compound Directory

Phenol red (CAS 143-74-8)

Grade: ACS reagent

Primary application: Phenol red can be used as a pH indicator in cell culture media (e.g., DMEM, RPMI-1640), as a colorimetric reagent for acid-base titrations, and as a reference standard for spectrophotometric calibration. Its absorbance maximum shifts from 432 nm (acidic form) to 558 nm (basic form), enabling quantitative pH measurement in biological systems.

Key features: High purity suitable for analytical procedures; stable crystalline form with long shelf life when stored desiccated; compatible with automated liquid handling systems for high-throughput screening.

View product details for Phenol red (CAS 143-74-8)

Selection Guide: How to Choose the Right Product

When selecting a pH indicator for research or production, consider the following decision framework:

Factor	Consideration for Phenol red
Application type	Cell culture media require non-toxic, sterile-filterable indicators; analytical titrations need high-purity ACS grade
Purity requirement	ACS reagent grade ensures ≤0.01% residual heavy metals and ≤0.5% loss on drying
pH range	Confirm that the 6.8–8.2 transition matches your experimental buffer system
Regulatory compliance	USP/EP monographs apply if used in pharmaceutical quality control; ACS grade satisfies general laboratory standards

For specialized applications requiring custom formulations—such as phenol red-free media for fluorescence-based assays—custom synthesis may be necessary, though standard ACS reagent grade suffices for routine pH monitoring.

Quality Considerations Across the Category

Specialty chemicals like Phenol red are subject to rigorous quality control. A typical Certificate of Analysis (CoA) for ACS reagent grade includes:

Assay by spectrophotometry (≥98% purity)
Loss on drying (≤0.5%)
Residue after ignition (≤0.1%)
Heavy metals (≤5 ppm as Pb)
pH transition interval verification

Regulatory frameworks from USP (United States Pharmacopeia) and EP (European Pharmacopoeia) provide official monographs for pH indicators, ensuring batch-to-batch consistency. For pharmaceutical applications, compliance with ICH Q7 guidelines for active pharmaceutical ingredient intermediates may also apply when Phenol red is used in drug formulation processes.

Industry Applications

Phenol red serves critical roles across multiple sectors. In biotechnology, it is incorporated into cell culture media formulations to monitor metabolic acidification—a rapid pH drop indicates bacterial contamination or cellular stress. The recent €4.8 million financing round for Aplagon’s antithrombotic APAC program (Manufacturing Chemist, June 2026) highlights the growing demand for reliable reagents in thrombo-inflammatory research, where pH indicators support assay development.

In clinical diagnostics, Phenol red is used in urine pH test strips and blood gas analysis calibration solutions. The ongoing expansion of AI-driven drug discovery, exemplified by Merck and Protillion’s $510 million collaboration (GEN, June 2026), underscores the need for high-purity specialty chemicals that provide reproducible results in automated high-throughput screening environments.

Sourcing Strategy

For bulk procurement of specialty chemicals, evaluate suppliers based on: (1) ISO 9001 certification for quality management systems, (2) availability of comprehensive CoA and SDS documentation, (3) lead time consistency for both small (gram) and large (kilogram) quantities, and (4) regulatory compliance support for USP/EP monograph adherence. Organizations requiring a consolidated supply of specialty chemicals can streamline procurement by working with a single qualified supplier to reduce qualification overhead and ensure consistent quality across the product range.

Contact our team to discuss your category-level sourcing requirements and receive a quotation.

Supplier Selection Guide

Research quantities of Phenol red (CAS 143-74-8) in ACS reagent grade are available from major suppliers. For bulk production, formal quotations with CoA, SDS, and lead time are available within 24 hours — contact our team to inquire about current pricing and discuss your requirements.

Q: What are Specialty Chemicals and what are they used for?
A: Specialty chemicals are high-purity compounds designed for specific applications such as pH indication, chromatography, or pharmaceutical synthesis. Phenol red (CAS 143-74-8) is used as a colorimetric pH indicator in cell culture media, diagnostic assays, and analytical chemistry.

Q: How do I select the right grade of Specialty Chemicals for my application?
A: Choose ACS reagent grade for analytical procedures requiring high purity and low heavy metal content. For cell culture applications, verify that the indicator is non-toxic and sterile-filterable. Always confirm the pH transition range matches your experimental buffer system.

Q: What quality documentation should I expect when purchasing Specialty Chemicals?
A: Expect a Certificate of Analysis (CoA) including assay purity, loss on drying, residue after ignition, and heavy metals content. For pharmaceutical-grade materials, request USP or EP monograph compliance documentation and batch-specific stability data.

Q: Can Specialty Chemicals be custom synthesized if my required specification is not listed?
A: Yes, many suppliers offer custom synthesis for specialty chemicals. For Phenol red, custom formulations such as phenol red-free media or deuterated analogs for mass spectrometry can be arranged with appropriate lead times and minimum order quantities.

Q: What are the typical lead times and MOQs for Specialty Chemicals?
A: Standard ACS reagent grade Phenol red is typically available from stock with lead times of 1–2 weeks. Minimum order quantities (MOQs) for research-grade material are often 1–10 grams, while bulk orders (kg scale) may require 2–4 weeks for production and quality release.