Complex Formation of Sudan I with Cu(II) and Its Identification from Chilli Species

The new chemical method for identifying and quantifying Sudan I (1-[(2,4-dimethylphenyl)azo]-2-naphthalenol) from chilli species is devised to overcome the shortcoming with complex operation, longer analytical period of High performance liquid chromatography (HPLC) assay. Sudan I complexed with Cu²⁺ leads to the shift of visible absorption wavelength from 478 nm to 526 nm. The major product is the Sudan I complex with general formula [Cu(Sudan I)]Cl. Bonds formed between Cu²⁺ and nitrogen, oxygen lead to a larger conjugated system, which accounts for the bathochromic shift. The effect of several factors is investigated. The optimum amount of NaOH (0.1 mol· I^-1) is 0.2 ml, and the appropriate reaction temperature is kept at 50°C. For the calibration of [Cu(Sudan I)]Cl, the limits of detection (3σ/m) is 0.446 mg·I^-1 and apparent molar absorptivity is about 1.094×10⁴ l·mol^-1 cm^-1. The recoveries (spiked in hot chilli pepper at the levels of 5 mg·kg^-1) range from 94% to 105%.