Meta Cresol Purple is a triarylmethane sulfonephthalein dye and pH indicator with the chemical formula C₂₁H₁₈O₅S and is also known as m-cresolsulfonphthalein. It is an acidic, hydrophobic compound that shows distinct color changes with variations in pH. The dye changes from red to yellow at approximately pH 1.2–2.8 and from yellow to violet at pH 7.4–9.0. These characteristic transitions make Meta Cresol Purple particularly useful for spectrophotometric pH measurements.
CAS No.: 63451-35-4
Synonyms: Hydroxy naphthol blue disodium salt, hydroxynaphthol blue indicator.
| Physical Properties | |
| Chemical formula | C21H18O5S |
| IUPAC Name | 4-[3-(4-hydroxy-2-methylphenyl)-1,1 -dioxo-2,1λ6-benzoxathiol-3-yl]-3-methylphenol |
| Molecular weight | 382.43 g/mol |
| Solubility | Soluble in water, sodium hydroxide solutions, and slightly soluble in alcohol |
| Appearance | Dark red to dark green or greenish-black crystalline powder |
| Storage | Store at room temperature |
| Chemical Properties | |
| Color | Dark green |
| Physical State | Solid |
| Melting Point | >250°C |
| λmax | 579nm, 371nm |
| Odor | Odorless |
| Pictograms : |  |
| Hazard Statements : | H302: Harmful if swallowed. H315: Causes skin irritation. H319: Causes serious eye irritation. H335: May cause respiratory irritation. |
| Precautionary Statements: | P261: Avoid breathing dust/fume/gas/mist/vapours/spray. P264: Wash hands thoroughly after handling. P270: Do not eat, drink or smoke when using this product. P271: Use only outdoors or in a well-ventilated area. P280: Wear protective gloves/protective clothing/eye protection/face protection. P302+P352: IF ON SKIN: Wash with plenty of soap and water. P304+P340: IF INHALED: Remove victim to fresh air and keep at rest in a position comfortable for breathing. P330: Rinse mouth. P362+P364: Take off contaminated clothing and wash it before reuse. P405: Store locked up. P501: Dispose of contents/container to in accordance with local regulation |
Meta Cresol Purple is a triarylmethane sulfonephthalein dye and pH indicator with the chemical formula C₂₁H₁₈O₅S and is also known as m-cresolsulfonphthalein. It is an acidic, hydrophobic compound that shows distinct color changes with variations in pH. The dye changes from red to yellow at approximately pH 1.2–2.8 and from yellow to violet at pH 7.4–9.0. These characteristic transitions make Meta Cresol Purple particularly useful for spectrophotometric pH measurements.
CAS No.: 63451-35-4
Synonyms: Hydroxy naphthol blue disodium salt, hydroxynaphthol blue indicator.
| Physical Properties | |
| Chemical formula | C21H18O5S |
| IUPAC Name | 4-[3-(4-hydroxy-2-methylphenyl)-1,1 -dioxo-2,1λ6-benzoxathiol-3-yl]-3-methylphenol |
| Molecular weight | 382.43 g/mol |
| Solubility | Soluble in water, sodium hydroxide solutions, and slightly soluble in alcohol |
| Appearance | Dark red to dark green or greenish-black crystalline powder |
| Storage | Store at room temperature |
| Chemical Properties | |
| Color | Dark green |
| Physical State | Solid |
| Melting Point | >250°C |
| λmax | 579nm, 371nm |
| Odor | Odorless |
| Pictograms : | |
| Hazard Statements : | H302: Harmful if swallowed. H315: Causes skin irritation. H319: Causes serious eye irritation. H335: May cause respiratory irritation. |
| Precautionary Statements: | P261: Avoid breathing dust/fume/gas/mist/vapours/spray. P264: Wash hands thoroughly after handling. P270: Do not eat, drink or smoke when using this product. P271: Use only outdoors or in a well-ventilated area. P280: Wear protective gloves/protective clothing/eye protection/face protection. P302+P352: IF ON SKIN: Wash with plenty of soap and water. P304+P340: IF INHALED: Remove victim to fresh air and keep at rest in a position comfortable for breathing. P330: Rinse mouth. P362+P364: Take off contaminated clothing and wash it before reuse. P405: Store locked up. P501: Dispose of contents/container to in accordance with local regulation |
Metacresol Purple is a triarylmethane dye used mainly as a pH indicator to measure acidity and alkalinity in chemical and environmental laboratories. It is also widely used for spectrophotometric pH measurements particularly in seawater and marine research.
Meta Cresol Purple changes from red to yellow in the acidic range and from yellow to violet in the higher pH range.
Metacresol purple can detect carbon dioxide through a pH-dependent color change. When carbon dioxide dissolves in water, it forms weak carbonic acid lowering the pH and changing the dye from purple to yellow. This response supports its use in colorimetric capnography and breath-based CO₂ indicators.
