On-line coupling of dynamic microwave-assisted extraction with high-performance liquid chromatography for determination of andrographolide and dehydroandrographolide in Andrographis paniculata Nees

A novel technique based on dynamic microwave-assisted extraction (DMAE) coupled on-line with high-performance liquid chromatography (HPLC) through a flow injection interface has been developed for determination of andrographolide and dehydroandrographolide in Andrographis paniculata Nees. A TM010 microwave resonance cavity built in the laboratory was applied to concentrating the microwave energy. An extraction vessel was placed in microwave irradiation zone. The extraction was performed in a recirculating system. When a number of extraction cycles were completed, the fractional extract (20 μL) was driven to the analytical column by 65% aqueous methanol and was measured by diode array detector (DAD) at 225 nm. The optimized extraction conditions are follows: extraction solvent 60% aqueous methanol; microwave forward power 80 W; extraction time 6 min; extraction solvent flow-rate 1.0 mL min−1. The detection and quantification limits obtained are 0.5 and 1.7 μg mL−1 for andrographolide and 0.6 and 1.9 μg mL−1 for dehydroandrographolide, respectively. The within-day and between-day precision (RSD) are 2.1% and 3.7% for andrographolide and 1.7% and 4.1% for dehydroandrographolide, respectively. Mean recoveries for andrographolide and dehydroandrographolide are 97.7% and 98.7%, respectively. Compared with ultrasonic extraction used in the Chinese pharmacopoeia, the proposed method was demonstrated to obtain higher extraction yield in a shorter time. In addition, only small quantities of solvent (5 mL) and sample (10 mg) were required.