SPECTROPHOTOMETRIC AND INFRARED ANALYSES OF THE TOXICITY LEVELS IN THE SELECTED WATER COLOURS IN PRIMARY SCHOOLS

Abstract

Ultraviolet-visible and Infra-red spectroscopy of twelve (12) common water colours available in two primary schools in Gwale Local Government area of Kano state Nigeria were examined, the UV-Vis of the colours showed that the λ_max range between 726 nm and 408 nm and tend to shift to longer wavelength which according to literatures, associate increase in λ_max with increase in conjugation and molecular structure of an organic compound. Also, the Molar Extinction Coefficient of the colours range between 3.5 x 10³ to 2.9 x 10⁴, with water colours (WC) 12 having the highest value. The values obtained, although within the acceptable level ≥ 1 × 10⁴ for most of the dyes, is low. Equally, the IR showed characteristic band in the range of 3428 - 3280 cm^-1, indicating the presence of O-H stretching vibration, 2937 – 2922 cm^-1 shows =CH₂ with saturated C-H stretching. The C–N stretching occurred at 2126 – 2109 cm^-1 while the carbonyl (C=O) stretching vibration appeared at 1689 – 1620. The azo (-N=N-) band occurred in the region of 1436 – 1420 cm^-1 with stretching vibration of azo group. A strong band at 1006 – 991 cm^-1is due to the stretching vibration of S=O  while the band at 879 – 864 cm^-1is due to the stretching vibration of C-Cl followed by C-Br group stretching vibration appearing at 790 - 745. The result depicts the characteristic azo chromophoric group, which, according to literature, can easily be reduced under mild reducing conditions, into forbidden aromatic amines such as benzidine, aniline and their derivatives. These compounds are toxic to the human body and are not eco-friendly. The implications of this and others for primary education were also examined. However, the UV-Vis and FT-IR spectroscopy of the water colours studied here did not reveal the chemical structure of the dyes; hence, there is a need to carry out GC-MS or NMR spectroscopy of the colours in order to determine their chemical structures.