Cresol Red

1. What is cresol red used for?

Cresol red is a pH-sensitive dye commonly used as a biochemical indicator in laboratory settings. It serves as a visual pH marker in cell culture media, electrophoresis buffers, and microbiological assays, typically transitioning from red to yellow around pH 7.2–8.8. Additionally, it is employed in titrations and as a tracking dye in agarose gel electrophoresis. Its ability to change color within a biologically relevant pH range makes it useful for monitoring metabolic activity in cell cultures, particularly in detecting acid production or alkaline shifts in microbial growth media.

2. Is cresol red hazardous?

Cresol red is generally considered low-toxic but should still be handled with care. While not highly hazardous, it can cause mild skin or eye irritation upon direct contact. Inhalation of dust or prolonged exposure should be avoided, as with most chemical dyes. It is not classified as a severe health risk, but proper lab safety measures—such as wearing gloves and goggles—are recommended. Environmental disposal should follow local regulations, as synthetic dyes can contribute to water pollution if released untreated.

3. What causes cresol red to change from red to yellow?

Cresol red changes color due to protonation and deprotonation of its sulfonephthalein structure in response to pH shifts. In alkaline conditions (pH > 8.8), it appears red as the dye loses protons (deprotonated form). As the pH drops below 7.2, it gains protons (protonated form), turning yellow. The transition occurs because the molecular structure alters light absorption properties, reflecting different wavelengths. This reversible change makes it ideal for pH monitoring in experiments where subtle shifts in acidity or alkalinity need visual detection.