phenol red

What is phenol red

**Introduction to Phenol Red** Phenol Red is a pH indicator dye widely used in biological and chemical laboratories to monitor pH changes in solutions. It exhibits a color transition from yellow (pH < 6.8, acidic) to red (pH 7.4–8.2, neutral) and pink (pH > 8.2, alkaline). Commonly added to cell culture media, Phenol Red helps visualize metabolic activity by indicating shifts in acidity due to cell growth. It is also employed in microbial assays, urine analysis, and respiratory studies. While non-toxic at low concentrations, its estrogen-like properties may interfere with sensitive experiments, prompting the use of Phenol Red-free alternatives in certain research applications. This versatile dye remains a staple in laboratory diagnostics and cell biology.

Preparation Process: Phenol red is prepared by sulfonating phenolsulfonphthalein. Dissolve 5 g of phenol in 10 mL of concentrated sulfuric acid at 0–5°C. Slowly add 2.5 g of phthalic anhydride while stirring. Heat the mixture at 100°C for 3 hours, then pour into ice water. Filter the precipitate and recrystallize from hot water. Alternatively, condense phenol with o-sulfobenzoic acid anhydride in the presence of zinc chloride at 120°C for 4 hours. Neutralize the product with sodium hydroxide to form the sodium salt. Purify by recrystallization from ethanol-water. The final product appears as a red crystalline powder.

Usage Scenarios: Phenol red is a pH indicator commonly used in cell culture, microbiology, and biochemical assays to monitor pH changes. It transitions from yellow (acidic, pH <6.8) to red (neutral, pH 6.8–8.2) and pink (basic, pH >8.2). In cell culture media, it helps visualize metabolic activity by indicating acid production. It is also used in urine pH tests, kidney function studies, and as a viability dye in cytotoxicity assays. Additionally, phenol red serves as a tracking dye in electrophoresis and in microbial growth media to detect pH shifts. Its low toxicity makes it suitable for biological applications.

phenol red Basic Info

phenol red Price