uranin

Uranin is the common name for fluorescein disodium salt, also known as uranine, a widely used fluorescent dye in tracer work. It is the sodium salt form of fluorescein and is valued for its bright fluorescence and relatively low toxicity in dilute solutions.

In water, fluorescein disodium is highly soluble and forms a bright yellow-green solution. When excited by blue or ultraviolet light, it emits green fluorescence, with typical excitation near 490 nm and emission near 520–530 nm. Its fluorescence can be detected at very low concentrations using fluorometric methods, making it suitable for tracing flows and movements in liquids.

The primary use of uranin is as a tracer in hydrology and environmental engineering. It is employed to map groundwater flow paths, determine connectivity between surface water and aquifers, and study reservoir or river mixing. It is also used for leak detection in water supply and cooling systems, as well as in soil and groundwater studies to visualize transport processes.

Detection and monitoring rely on fluorometry, spectrophotometry, or ultraviolet visualization, often after sample concentration or pre-treatment to enhance sensitivity. The dye is chosen for its visibility, relative stability, and ease of detection, though it can degrade under strong sunlight and high temperatures and can stain surfaces.

Historically, fluorescein was synthesized in the 19th century, and the uranin brand became widely used in Europe for human-made tracer studies. Today, fluorescein disodium salt remains a common, portable tracer option in environmental science and engineering, valued for its clear, observable fluorescence and straightforward analysis.