o-Cresolphthalein

What is o-cresolphthalein?

o-Cresolphthalein is an organic compound belonging to the phthalein family of dyes, chemically derived from cresol and phthalic anhydride. This synthetic compound appears as a white to pale yellow crystalline powder in its pure form, which dissolves in alcohol and alkaline solutions to produce an intense violet-red color. Its molecular structure features a central carbon atom bonded to two phenolic rings and a phthalide group, creating a conjugated system responsible for its chromogenic properties. The "o-" prefix indicates the ortho position of the methyl group on its phenolic rings, distinguishing it from other cresolphthalein isomers. This specific structural arrangement gives o-cresolphthalein unique chemical properties that make it particularly useful as a pH-sensitive indicator in various analytical applications.

What is the o-Cresolphthalein indicator?

The o-Cresolphthalein indicator is a pH-sensitive dye that undergoes a distinct color change from colorless to violet-red between pH 8.2 and 9.8, making it valuable for alkaline range determinations. In clinical chemistry, it serves as the basis for a highly specific colorimetric method to measure serum calcium levels, where it forms a stable red complex with calcium ions in alkaline medium. The indicator's transition range is particularly useful for monitoring biochemical reactions that occur under mildly alkaline conditions. Its molecular structure allows it to function as both a pH indicator and a metallochromic agent, enabling dual applications in acid-base titrations and metal ion detection. This versatility has established it as a standard tool in both medical diagnostics and chemical analysis.

What is the advantage of o-Cresolphthalein?

The primary advantage of o-Cresolphthalein lies in its exceptional selectivity for calcium ions in alkaline conditions, making it irreplaceable for clinical calcium determinations. Unlike many pH indicators, it maintains excellent chemical stability and color intensity across repeated pH cycles. The compound's sharp endpoint transition allows for precise visual and spectrophotometric measurements in analytical procedures. Its calcium complex exhibits high molar absorptivity, enabling sensitive detection at low concentrations. The indicator's dual functionality as both a pH probe and metal ion detector provides unique analytical flexibility. Furthermore, its relatively simple molecular structure contributes to consistent performance and reproducibility, while remaining cost-effective for routine laboratory use. These combined advantages make it superior to many alternative indicators for specific clinical and chemical applications.