Rapid visual and spectrophotometric nitrite detection by cyclometalated ruthenium complex

Quantitative determination of nitrite ion (NO₂¯) is of great importance in environmental and clinical investigations. A rapid visual and spectrophotometric assay for NO₂¯ detection was developed based on a newly designed ruthenium complex, [Ru(npy)([9]aneS3)(CO)](ClO₄) (denoted as RuNPY; npy = 2-(1-naphthyl)pyridine, [9]aneS3 = 1,4,7-trithiacyclononane). This complex traps NO⁺ produced in acidified NO₂¯ solution, and yields observable color change within 1 min at room temperature. The assay features excellent dynamic range (1–840 μmol L⁻¹) and high selectivity, and its limit of detection (0.39 μmol L⁻¹) is also well below the guideline values for drinking water recommended by WHO and U.S. EPA. Practical use of this assay in tap water and human urine was successfully demonstrated. Overall, the rapidity and selectivity of this assay overcome the problems suffered by the commonly used modified Griess assays for nitrite determination.