A new and sensitive resonance-scattering method for determination of trace nitrite in water with rhodamine 6G

In the medium HCl–KI–rhodamine dye, NO₂^– reacts with excess I^– to form I₃^– and the I₃^– and rhodamine dye combine to form an association particle which gives three resonance-scattering (RS) peaks at 320 nm, 400 nm, and 595 nm. In systems containing rhodamine 6G (Rh6G), rhodamine B (RhB), rhodamine S (RhS), and butyl rhodamine B (BRhB) the resonance scattering intensity at 400 nm is proportional to nitrite concentrations in the range 2.3–276 ng mL^–1, 9.2–184 ng mL^–1, 9.2–184 ng mL^–1, and 9.2–92 ng mL^–1, respectively. Because of the high sensitivity, wide linear range, and good stability of the Rh6G system, it has been used for determination of nitrite in water samples, with satisfactory results. The spectral results have been used to verify that the formation of (Rh6G·I₃)_n association particles and their interface with the system are main factors that cause the RS enhancement.