Spectroscopic study of orange G–β-cyclodextrin complex and its analytical application

The mechanism of the inclusion of orange G and β-cyclodextrin (β-CD) has been studied by using both spectrophotometry and infrared spectroscopy. Effects of the pH, concentrations of β-CD, and ionic strength on the inclusion complex of β-CD and orange G were examined. The result showed that orange G reacts with β-CD to form a 1:1 host–guest complex with an apparent formation constant of 3.03 × 103 mol−1 l. The thermodynamic parameters of inclusion complex, ΔG0, ΔH0, and ΔS0 were obtained. Based on the enhancement of the absorbance of orange G produced through complex formation, a ratiometric method spectrophotometrically for the determination of orange G in bulk aqueous solution in the presence of β-CD was developed, which overcome the effect of condition change on the determination of orange G. The linear relationship between the absorbance and orange G concentration was obtained in the range of 1.0 × 10−5 to 4.0 × 10−5 mol l−1, with a correlation coefficient of 0.9998. The detection limit was 3.6 × 10−6 mol l−1. The principal advantage of the proposed method is high accuracy because ratiometry was used in measurement.