Isosbestic Point of Traditional Chinese Medicine Injections (TCMIs) and Its Practice in Evaluating TCMIs’ Stability

Abstract

The aim of the study was to discover the isosbestic point of Traditional Chinese
Medicine Injections (TCMIs) and to verify its practice in evaluating TCMIs’ stability. Six
TCMIs (Qingkailing, Shuanghuanglian, Danshen, Dengzhanxixin, Honghua, and Shuxuening
Injection) were kept at 60 oC, and solutions of 1 ml were sampled when heated for 0, 1, 2, 3, 4, or 8 weeks. Samples were diluted and their ultraviolet-visible spectrum was scanned from 230-800 nm. Isosbestic point of the TCMI was picked out. AUCB (area under the spectrum curve before the isosbestic point) or AUCA (AUC after the point) was obtained, and the BA ratio was calculated by AUCB/AUCA. HPLC-fingerprints of the sample were performed and total area of fingers (TAF) was calculated. TCMIs’ color was darkened when heated for weeks. During heating, AUCB decreased and AUCA increased, while BA ratio was increasing. The value of BA ratio from all the heated TCMIs was ten percent smaller than that of the original one, so do the results of HPLC-fingerprints except Honghua Injection. There was a good relationship between BA ratio and TAF except Honghua Injection. All the results suggested that isosbestic point existed, and BA ratio was a sensitive index to evaluating TCMIs’ stability.