A novel spectrophotometric method for the rapid determination of the degree of acetylation in cellulose acetate

Abstract A rapid, accurate, and cost‐effective spectrophotometric method has been developed for determining the degree of acetylation (DA) of cellulose acetate (CA). The method is based on the ferric hydroxamate principle. A mixed solvent system of dichloromethane and methanol (7:3, v/v) was optimized via Hansen solubility parameter theory to ensure complete dissolution of CA across a wide DA range (1.83–2.95). The reaction of CA with hydroxylamine to form the corresponding hydroxamic acid was systematically optimized, achieving >98.8% conversion within 20 min at 25°C. Subsequent complexation with Fe(III) ions produced a stable, purple‐colored chelate with a maximum absorbance at 520 nm. Fourier transform infrared (FTIR) analysis confirmed the complete conversion, as evidenced by the disappearance of the ester CO stretch (~1740 cm −1 ) and the appearance of a broad OH stretch (~3400 cm −1 ). The method obeys Beer–Lambert law over a concentration range of 0.05–2.5 mg mL −1 , with a molar absorptivity of 1.09 × 10 3 L mol −1 cm −1 and a correlation coefficient ( r ) of 0.999. The limits of detection and quantification were 0.012 mg mL −1 and 0.036 mg mL −1 , respectively. Validation studies confirmed excellent precision (RSD <2%), high accuracy (recovery 98.5%–101.2%), and no significant statistical difference compared to the standard titration method ( t ‐test and F ‐test, p > 0.05). This method offers a simple, reliable, and inexpensive alternative to conventional techniques for the routine analysis of CA acetylation.