Spectrophotometric determination of N-(1-naphthyl)ethylenediamine in aqueous solution by coupling with diazotised 4-aminoacetophenone

Abstract

The coupling reaction of N-(1-naphthyl)ethylenediamine (N-NED) with diazotised 4-aminoacetophenone in acidic media has been studied in order to determine its ability to serve as the basis of a sensitive spectrophotometric method for the determination of N-NED in aqueous solution. The intense reddish purple monoazo dye formed shows a maximum absorption at 550 nm, and is water soluble and stable. A graph of absorbance versus N-NED concentration is linear, indicating that Beer's law is adhered to over the range 4.4–88 µg of N-NED in a final volume of 25 ml, i.e., 0.18–3.5 p.p.m. of N-NED, with a molar absorptivity of 5.61 × 10⁴ l mol^–1 cm^–1, a sensitivity index of 0.0033 µg cm^–2, a relative error from -0.9 to +3.8% and a relative standard deviation from 0.2 to 4%, depending on the N-NED concentration. The optimum conditions for the colour reaction and the interference of foreign organic compounds have been investigated. The method is simple and rapid and needs neither temperature control nor solvent extraction techniques.