Phenol red

Phenol red, also known as phenolsulfonphthalein (PSP), is a widely used pH indicator in scientific research and everyday applications. Its color-changing properties make it particularly useful in cell biology, environmental testing, and optical technologies.

🧪 Applications
• Photodiode Fabrication:
Phenol red can be used as a dye in the creation of phenol red/n-type silicon photodiodes using spin coating techniques. These devices are highly suitable for photodetection applications.
• Fiber Optic pH Sensors:
Due to its distinct color shifts in response to acidity, phenol red serves as a reliable dye in fiber optic pH sensors. As acidity increases, the dye’s absorption spectrum transitions from the green to the blue region.
• Freshwater pH Testing:
It acts as an effective pH indicator for analyzing the pH levels of freshwater sources.

Use in Swimming Pool Test Kits:
Phenol red is a standard reagent in home swimming pool test kits, sometimes labeled under alternate names like “Guardex Solution #2”. It is used to measure water pH levels, but its performance can be influenced by other chemicals in the pool:
• Chlorine Sensitivity:
High chlorine levels can bleach phenol red unless thiosulfate is added to neutralize chlorine’s oxidizing effects.
• Reaction with Bromine:
Excessive bromine can convert phenol red into bromophenol red, shifting its pKa and causing pH readings to appear falsely higher (e.g., pH 6.8 might be misread as 7.5).
At very high bromine levels (>20 ppm), a further conversion to bromophenol blue may occur, significantly lowering the pKa and giving the misleading impression of a very high pH, while the water may in fact be dangerously acidic.