Dyes

Introduction Fluorescein is a synthetic fluorescent dye known for its bright yellow-green fluorescence under suitable lighting conditions. It belongs to the xanthene dye family and is used in analytical chemistry, laboratory testing, microscopy, and select industrial applications that require fluorescence detection. Also identified as Solvent Yellow 94, Fluorescein is available in different chemical forms and grades. Its performance depends on factors such as purity, solubility, pH, concentration, and the conditions in which it is used. For manufacturers, distributors, and industrial buyers, understanding these properties is important before selecting a suitable grade. This guide covers Fluorescein’s chemical identity, applications, product specifications, quality requirements, and sourcing considerations. What Is Fluorescein (Solvent Yellow 94)? Fluorescein is an organic synthetic dye with the molecular formula C20H12O5 and a molecular weight of approximately 332.31 g/mol. Its CAS number is 2321-07-5. It is generally supplied as a yellow powder or orange-red crystalline material. One of its main characteristics is its strong yellow-green fluorescence under suitable light, particularly in alkaline solutions. Key chemical identification details: Chemical nameFluoresceinCommon nameSolvent Yellow 94CAS number2321-07-5Molecular formulaC20H12O5Molecular weight332.31 g/molChemical familyXanthene dyesAppearanceYellow powder or orange-red crystalsWater solubilityInsoluble in waterSolubilitySoluble in dilute aqueous bases One important distinction is between Fluorescein and Sodium Fluorescein. Sodium

Introduction Dye purity and assay value are closely related, but they do not always mean the same thing. Understanding the difference helps manufacturers evaluate technical specifications, compare suppliers, and select synthetic dyes for food, cosmetic, and industrial applications.A dye with a high assay value is not automatically suitable for every application. Buyers must also consider the test method, moisture content, residual salts, specified impurities, and applicable regulatory requirements. For example, the U.S. Food and Drug Administration (FDA) evaluates color additives against defined identity, composition, purity, and use requirements.For product developers and procurement teams sourcing from dyes manufacturers in India or other global markets, understanding these specifications is an important part of supplier evaluation. What Is Dye Purity? Dye purity refers to how closely a dye material meets its defined chemical identity and composition requirements, including limits on unwanted substances. However, the exact meaning of a reported purity percentage depends on the specification and analytical method used. A dye sample may contain the intended coloring compound along with moisture, residual salts, unreacted starting materials, or other related compounds. These components can affect the reported composition and may influence how the material performs in a formulation. For example, a buyer evaluating a

Introduction pH is one of the most important process conditions when using synthetic dyes. A small pH change can affect dye solubility, dye uptake, color strength, shade development, leveling, and, in some cases, dye stability. However, no single pH value works for every synthetic dye. Acid dyes, reactive dyes, disperse dyes, and other dye classes have different chemical structures and application requirements. The substrate also matters. A pH that works well for wool may not suit polyester or cotton. For manufacturers and industrial buyers, controlling pH is therefore not simply about choosing an acidic or alkaline bath. It is about matching the dye chemistry and application process to the correct operating range.  Why Does pH Matter in Synthetic Dye Applications?  pH changes the chemical environment in which a dye interacts with water, auxiliaries, and the substrate Depending on the dye system, pH can influence: Dye solubility and dispersion Dye-fiber attraction Dye uptake and exhaustion Reaction between dye and fiber Color strength and shade Leveling and migration Dye stability during processing Final color fastness This is why uncontrolled pH can result in uneven shades, lower color yield, poor reproducibility, or unwanted changes during processing. The exact effect, however, depends on the