Fluorescein, also known as fluorescent yellow, fluorescent dye, or fluorescent red. There are two variants: stable red variant B and yellow variant A. The molecular formula is C20H12O5 and the molecular weight is 332.31. B is a red crystalline powder with green fluorescence. Melting point 314-316 * C (decomposition). Soluble in hot alcohols, hot aniline, hot acetone, and hot formic acid, slightly soluble in water, alcohols, ethers, and acetic acid, insoluble in petroleum ether. A is a yellow amorphous powder with a melting point of 314-316 ℃. Soluble in acetone, methanol, formic acid, slightly soluble in water, alcohol, ether, chloroform, benzene, acetic acid, xylene, nitrobenzene, insoluble in petroleum ether. When heated, it turns into a red variant. Used as an indicator and biological staining agent for chemical analysis. Obtained by reacting resorcinol with phthalic anhydride.
Instructions for the use of fluorescein:
1. Antifreeze is an important pigment that can make antifreeze appear green fluorescent.
2. Used as indicators for chemical analysis, biological dyes, and cosmetic coloring agents.
3. Adsorption indicator for precipitation titration:
Prepare a 0.1% ethanol solution or prepare a 1% aqueous solution using its sodium salt. Titrate Cl -, Br -, I -, SCN -, CN -, C2O42-, SO42-, CO32-, etc. with Ag+. In neutral or weakly alkaline media, the color of the titration endpoint changes from yellow green to rose red.
4. Fluorescein is the matrix of luminescent substances. Substances that make many organisms fluorescent. It forms a complex with ATP (fluorescein adenosine) and then binds to luciferase. Fluorescein luminescence activated during oxidation process. The entire reaction is used for the detection of living organisms or for quantitative analysis of very low levels of bacterial contamination. For example, using a fluorescence spectrophotometer for measurement.