Parameters Affecting the Peroxyoxalate Chemiluminescence

ABSTRACT

A careful study of the parameters affecting the chemiluminescent reaction of TCPO (bis(2,4,6-trichlorophenyl)oxalate) and 2-NPO (bis(2-nitrophenyl)oxalate) with hydrogen peroxide, in the presence of imidazole (used as buffer and catalyst) and the fluorophore 3-AFA (3-aminofluoranthene), was carried out in acetonitrile/water medium. The data are reported in terms of the time (t_Imax) required for the relative maximum chemiluminescence intensity (I_max) and the area (A) under the curve of intensity νs. time. At controlled acidity and high unprotonated imidazole concentration ([IMI] = 1x10⁻² mol.L⁻¹), the I_max and t_Imax values do not depend on the acetonitrile/water ratio. The CL intensity is maximum at around pH 6.0 (higher buffer capacity). For 1x10⁻² < [IMI] < 1x10⁻⁴ mol.L⁻¹, the area is largest when [IMI] = 1x10⁻³ mol.L⁻¹ and linearly dependent on the hydrogen peroxide concentration (10⁻⁵ − 10⁻³ mol.L⁻¹). The area is also enhanced by increasing the fluorophore concentration. The acidity controls the unprotonated imidazole and H⁺ concentration. Several errors can arise from quantitative analyses carried out without control of the HIMI⁺ and IMI concentrations.

Keywords::

• chemiluminescence
• peroxyoxalate
• imidazole