Quinaldine red (pronounced /ˈkwɪnəldiːn/, abbreviated QR)[3] is a dark green–red or black solid that does not dissolve easily in water (it is partly miscible).

The reaction rate eventually levels off due to the maximum formation of the product within the oxidation process.

Quinaldine red can exhibit fluorescence when it is bound to nucleic acids, which then emit radiation between 580-650 nm.

QR is dissolved in a mixture of water, ethanol, isopropyl alcohol, glycerol, and other solvents and is placed on the teeth.

In the presence of oxygen, the QR and carrier particles solution uses its sensitivity to light energy to ultimately bleach teeth, making them whiter.

In an assay for inorganic and organic phosphates, QR proved to be a better indicator due to a low blank and its color stability.

In this case, if pale pink mixture of quinaldine red turns to a colorless solution, this indicates the presence of a free phosphate.

If the solution turns a dark red, that indicates the phosphomolybdate complex ion has formed.