Eosin Indicator
Overview
Eosin Indicator is a synthetic brominated derivative of fluorescein, primarily used as a biological stain and pH indicator. Its vibrant pink-red color makes it indispensable in histology for highlighting cytoplasmic structures in tissue samples. The dye is chemically stable and exhibits fluorescence under ultraviolet light, expanding its utility in microscopy and diagnostic applications. First synthesized in the late 19th century, eosin remains a cornerstone in laboratory workflows due to its compatibility with aqueous and alcoholic solutions. It is commercially available in multiple variants, including Eosin Y (yellowish shade) and Eosin B (bluish shade), with Eosin Y being the most widely used in scientific settings.
Physical and Chemical Properties
Eosin Indicator appears as a reddish-brown crystalline powder with high solubility in water (up to 10% w/v) and moderate solubility in ethanol. Its absorption spectrum peaks at 515–520 nm, producing a distinct red fluorescence when excited by UV light. The compound decomposes at temperatures exceeding 300°C without melting. As a pH indicator, eosin transitions from colorless to pink between pH 0–3, making it useful for acidic range determinations. Its sodium salt form enhances water solubility, while the free acid variant is preferred for organic solvent-based applications. The dye is photostable but may degrade under prolonged exposure to strong oxidizers.
Main Applications
In histopathology, eosin is paired with hematoxylin in the H&E stain to differentiate cellular components, with eosin staining cytoplasm and extracellular matrices pink. This application accounts for over 70% of its industrial use. The dye also serves as a pH indicator in titration experiments and quality control processes for acidic products. Additional applications include textile dyeing, red ink formulation, and as a tracking dye in electrophoresis. Recent research explores its potential in photodynamic therapy due to its light-activated properties. Industrial users should note that technical-grade eosin is suitable for staining, while analytical-grade material is required for precise pH measurements.
Safety and Storage
Eosin Indicator is classified as a mild irritant to skin and eyes. Laboratories should implement standard PPE protocols, including gloves and safety goggles, when handling the powder or concentrated solutions. Inhalation of dust particles may trigger respiratory discomfort, necessitating use in well-ventilated areas or under fume hoods. For long-term storage, keep containers tightly sealed in dark conditions at room temperature (15–25°C). Moisture-sensitive batches may require desiccants. Shelf life typically exceeds three years when stored properly. Spills should be contained with absorbent materials and disposed of as chemical waste according to local regulations.
B2B Procurement Guide
Bulk purchasers should specify required purity levels: histological grade (≥85% dye content) for staining applications versus analytical grade (≥95%) for quantitative work. Packaging options range from 25g bottles to 25kg drums, with price breaks at the kilogram scale. Leading manufacturers include Sigma-Aldrich, Thermo Fisher, and domestic specialty chemical suppliers. Key procurement considerations include batch-to-batch color consistency (verified by spectral analysis), heavy metal impurity limits (<10 ppm), and solubility testing results. Some suppliers offer customized formulations with enhanced solubility or fluorescence intensity. For international shipments, verify compliance with destination-country chemical regulations, particularly regarding brominated compounds.
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