Detection of biogenic amines using a nitrated conjugated polymer

Nitrated polythiophene (NPTh) was examined for the detection of amine vapors. When the polymer film was exposed to vapors of biogenic amines (BAs) such as ethylenediamine, putrescine, and cadaverine, its color darkened instantly. Accordingly, the ultraviolet-visible (UV–vis) absorption spectra showed a significant hyperchromic shift, indicating the formation of an intermolecular charge transfer complex (NPTh^δ+-BA^δ−) between the polymer and analyte. On the other hand, the change in absorption was relatively small for non-BA vapors. The absorption response rates of NPTh to the BAs were quite different because of the differences in their saturated vapor pressures. A linear relationship between vapor concentration (z) and absorption change (y: A/A₀, where, A and A₀ are the absorbances after and before exposure to the amine, respectively) was established, given by the equation z = k(y–1), where k = (conc_sat/t_eq)/a, conc_sat is the saturated vapor concentration, and t_eq is the exposure time necessary to reach an equilibrium in the absorption change. The k values for ethylenediamine, putrescine, and cadaverine were determined to be 5.01 × 10³, 0.83 × 10³, and 0.40 × 10³ ppm, respectively. This equation can be used to determine the unknown BA vapor concentration by UV–vis spectroscopic analysis.