Evaluation of Fourier transform-near infrared spectroscopic measurements for the quantification of curcumin in turmeric herbal medicines

摘要

In this investigation, Fourier transform-near infrared (FT-NIR) spectroscopy was used to determine the curcumin content in commercial turmeric herbal medicines. Two different sample presentations originating from a turmeric capsule and powder were evaluated and compared using an FT-NIR spectrometer equipped with a 30-capsule sample plate in the wavenumber region of 11,500-6000cm~(-1) (transmittance mode) and a 6-vial sample plate in the wavenumber region of 10,000-4000cm~(-1) (reflectance mode), respectively. One hundred and forty samples of turmeric herbal medicines were divided into two sets: a training set with 110 samples and a prediction set with 30 samples. High-quality FT-NIR spectra for the turmeric powder containing the informative regions of curcumin (6850, 6000 and 4600 cm~(-1)) were obtained while collecting FT-NIR data on the powder samples in the glass vials. A successful partial least-squares calibration model for curcumin content in commercial turmeric herbal medicine powders was then obtained by utilising the entire spectral region (10,000-4000 cm~(-1)) as well as a second derivative spectral pretreatment containing seven principal components. The best model for predicting curcumin in 30 test samples returned a coefficient of determination (r~2) of 0.98, a root mean squares error of prediction (RMSEP) of 0.13% that was only 1.35 times the standard error of laboratory and a ratio of RMSEP to the standard deviation of curcumin content in the prediction set (RPD) of 7.76. These statistical values confirmed the high predictive performance of this model. All these results confirm that the use of turmeric herbal medicine powder and a wide informative wavenumber range of 10,000-4000cm~(-1) can increase the efficacy of FT-NIR spectroscopy for the rapid and non-destructive analysis of curcumin content in commercial turmeric herbal medicines. By contrast, models developed for determining curcumin in turmeric contained in capsules were not suitable for analytical purposes.