A simple colorimetric method for aromatic amine and its application

This work developed a simple colorimetric reaction for the determination of aromatic amines which was divided into two parts. Part I studied the colorimetric reaction for seven aromatic amine including diphenylamine (DPA), 2-aminodiphenyl (2-ADP), 4-aminodiphenyl (4-ADP), 2-phenylenediamine (2-PDA), 4-phenylenediamine (2-PDA), 2-nitroaniline (2-NA), and 1-nephthylamine (1-NTA). The reaction was studied by type, concentration, and volume of acids, concentration and volume of sodium nitrate (NaNO3), reaction time, and temperature. Under optimized conditions, the reaction colors of DPA, 2-ADP,4-ADP, 2-PDA,4-PDA,2-NA and 1-NTA were blue, dark pink, red, brown, light chartreuse, and violet respectively. The linear range concentration were at 5-50, 1.5-85, 1.5-15, 20-150, 5-100, 20-500 and 0.25-5 ppm. Part II studied a colorimetric method using the application on a mobile phone (CAnal) to detect diphenylamine (DPA) in propellants, gunshot residues, apples, and Chinese pears compared with UV-Vis spectrophotometer and gas chromatography-frame ionization detector (GC-FID). A home-made controlled light box was created to improve the precision and accuracy. Under optimized parameters, the calibration curve was obtained from green value to give a linear range from 0.1 to 20 ppm with detection limit of 0.098 ppm. The determination of DPA in propellants, gunshot residues, apples, and Chinese pears was also demonstrated with acceptable performance being in agreement with the data from UV-Vis spectrophotometer and gas chromatograph-frame ionization (GC-FID). The results suggested the potential for rapid, portable, and simple detection for application in field tests.