Abstract: Objective To detect the illegally added gliclazide and hydrochlorothiazide in capsule preparations with the near infrared (NIR) correlation coefficient method. Methods The near infrared spectrum of the chemical reference substance of gliclazide and hydrochlorothiazide was used as reference spectrum, the specific spectrum was selected. According to the added amount of gliclazide and hydrochlorothiazide in capsule preparations, the threshold value of similarity coefficient in this spectral band of the tested sample spectrum and the reference spectrum was established. Whether the tested sample contained gliclazide or hydrochlorothiazide was qualitatively estimated. Results The spectral band 5 850～5 700 cm-1 was selected as the characteristic band for gliclazide, and the threshold value was set as 60%. The spectral band 6 150～5 950 cm-1 was selected as the characteristic band for hydrochlorothiazide, and the threshold value was set as 70%. Conclusion The two models have high accuracy and strong applicability, which may be used as a fast detection method to determine illegally added gliclazide and hydrochlorothiazide in traditional Chinese medicine and health food capsule preparations on market.

Key words: near infrared diffuse reflection spectrum, correlation coefficient method, qualitative analysis, illegal addition, gliclazide, hydrochlorothiazide