Nanoscale analysis of pharmacologically active catechins in body fluids by HPLC using borate complex extraction...

A pretreatment method based on borate complex formation is described for the selective and simultaneous quantitation of pharmacologically active catechins in human plasma and saliva. This method is based on the interaction of catechins with diphenylborate (as a complexing agent) and tetra-n-butylammonium (as a counter ion) in alkaline media to give the catechin-diphenylborate complex and ion-pair that are extractable to the organic phase. The complex extracted in an organic solvent is dissociated by shaking with an aqueous trifluoroacetic acid solution to back-extract free catechins to the aqueous phase, followed by high-performance liquid chromatography (HPLC) analysis with fluorometric and diode array detection. Under optimal conditions, all catechins originating from green tea extracts were selectively purified from plasma and saliva samples, and they were stabilized during the extraction procedures by forming the complex. The nano-scale quantitative analysis of eight catechins was achieved with high recovery and analytical reproducibility. The proposed method would be a useful tool for pharmacokinetic studies of catechins in plasma and saliva.