Fundamental and Applied Studies on Chromatographic Separation of Cold Drugs and Skincare Creams and Extraction of Salvia miltiorrhiza using Subcritical Water

Abstract

Subcritical water chromatography (SBWC) and subcritical water extraction (SBWE) are two green techniques that use subcritical water as the sole solvent for separations, thus eliminating the use of toxic and expensive organic solvents. This dissertation research was mainly focused on the development of SBWC through both fundamental and applied studies. Fundamental studies include the solubility of parabens and stability of preservatives and stationary phases under subcritical water conditions. Solubility of parabens increased by 11 to 36 folds with temperature raise from 25 to 150 °C, but decreased at 200 °C due to degradation. A new approximation model developed in this work successfully estimated the solubility of parabens in subcritical water. The studies on the stability of preservatives in subcritical water revealed that the preservatives were stable up to 150 °C and there was approximately 10% degradation of preservatives at 200 °C. The stationary phase evaluation indicated that the Waters XBridge C18 and phenyl columns were stable for up to 30,000 column volume at 150 °C and the ZirChrom-DB-C18 column up to 14,250 column volume at 200 °C. Applied studies of SBWC were focused on separation and analysis of pharmaceuticals from cold drugs and niacinamide, preservatives, and sunscreens present in skincare products. Our best SBWC quantification results achieved in this work are in the range of 97.4 to 103.4% recoveries and RSDs less than 1.9%. A large number of replicate chromatographic runs and the comparison with high performance liquid chromatography results indicate that our SBWC methods for niacinamide and preservatives are quite accurate and precise. The Subcritical water extraction and traditional herbal decoction (THD) of Salvia miltiorrhiza were carried out and the herbal extracts were tested for cytotoxicity on Caenorhabditis elegans. In general, the concentration of anticancer agents obtained by SBWE increased by 4 to 18 folds when the temperature was raised from 75 to 150 °C. The concentration of tanshinones, important anticancer agents, obtained by SBWE at all four temperatures was higher than that of the THD. Similarly, the cytotoxicity tests revealed that the SBWE herbal extracts were more potent than the THD extracts.