Overview
Alizarin indicator is a synthetic organic compound derived from the natural dye alizarin, historically extracted from madder root. It belongs to the anthraquinone family and is widely used as a pH indicator due to its distinct color transition in weakly acidic to neutral solutions (pH 5.5–6.8). Beyond its role in analytical chemistry, it serves as a metallochromic indicator for complexometric titrations, particularly with metals like aluminum and zirconium. In industrial contexts, alizarin indicator is valued for its stability and reproducibility. Its dual functionality as both a dye and a chelating agent makes it versatile for laboratory and niche manufacturing applications, such as textile dyeing and metal ion detection.
Physical and Chemical Properties
Alizarin indicator appears as an orange-red crystalline powder with a molecular weight of 240.21 g/mol. It exhibits moderate solubility in organic solvents like ethanol and diethyl ether but limited solubility in water. The compound’s melting point ranges between 289–290°C, and it decomposes upon further heating rather than boiling. Its key chemical property is the reversible color change from yellow (acidic) to red (alkaline), attributed to protonation/deprotonation of its hydroxyl groups. The indicator also forms colored complexes with metal ions, a trait exploited in titrimetric analysis. Its stability under standard storage conditions (room temperature, dry environment) ensures a long shelf life.
Main Applications
The primary use of alizarin indicator is in pH monitoring, especially in titrations requiring precise endpoint detection near pH 6. It is a preferred choice for EDTA titrations of aluminum, fluoride, and rare-earth metals due to its sharp color transition in the presence of these ions. Beyond laboratories, it finds niche roles in textile dyeing (as Mordant Red 11) and as a histological stain. In education, it demonstrates acid-base equilibria and metal-ligand interactions. Industrial quality control processes may employ it to trace metal impurities or monitor reaction progress.
Safety and Storage
Alizarin indicator poses low acute toxicity but may irritate the skin, eyes, or respiratory tract upon direct contact. Proper personal protective equipment (PPE)—gloves, goggles, and lab coats—is recommended during handling. Avoid creating dust or aerosols. Storage requires protection from light, moisture, and extreme temperatures to prevent degradation. Sealed containers in well-ventilated areas are ideal. Spills should be neutralized with a mild alkali (e.g., sodium bicarbonate) and cleaned promptly. Disposal must comply with local regulations for organic compounds.
B2B Procurement Guide
When sourcing alizarin indicator, prioritize suppliers with certifications (e.g., ISO, GMP) to ensure consistency and traceability. Key specifications include purity (≥95% for most applications), CAS number verification (72-48-0), and packaging (amber glass bottles to prevent photodegradation). Bulk purchases (kilograms) may reduce costs by 10–20%, but evaluate shelf-life constraints. Request SDS and batch-specific testing reports. For international shipments, confirm compliance with chemical transport regulations. Alternatives like alizarin red S (water-soluble variant) may suit specific needs.
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