Qualitative and quantitative analysis of curcumin in dried ginger by the resonance Rayleigh scattering technique and absorption spectroscopy

Abstract

On the basis of our qualitative analysis, two new methods of the resonance Rayleigh scattering (RRS) and multiwavelength visible absorption spectroscopy (VIS) for the determination of curcumin in dried ginger are established. At pH 6.70 Tris-HCl, curcumin reacts with brilliant green to form binary ionic association complexes. Curcumin was determined by the RRS method at 347 nm, and the detection limit and quantitative limit were 0.0018 mg · L−1 and 0.047 mg · kg−1, respectively. In addition, curcumin was also determined by single-wavelength, dual-wavelength, and three-wavelength VIS at 429 nm, 570 nm, and 656 nm, respectively. The detection limit, quantitative limit, and apparent molar absorption coefficient are, respectively, 0.025 mg · L−1, 0.65 mg · kg−1, and 1.03 × 105 L · mol−1 · cm−1 (429 nm or 656 nm); 0.028 mg · L−1, 0.73 mg · kg−1, and 7.89 × 104 L · mol−1 · cm−1 (570 nm); 0.013 mg · L−1, 0.33 mg · kg−1, and 2.06 × 105 L · mol−1 · cm−1 (429 nm + 656 nm); 0.009 mg · L−1, 0.23 mg · kg−1, and 2.85 × 105 L · mol−1 · cm−1 (429 nm + 570 nm + 656 nm). Taking the RRS method and dual-wavelength VIS (DWO–VIS) with moderate sensitivity as examples, the detection results of curcumin in dried ginger samples are compared, and there are no significant differences in accuracy and precision between the two new methods. The two methods are accurate, reliable, and highly sensitive for the determination of curcumin in commercially available dried gingers, and the results are satisfactory.