The motivation for developing this microwave-assisted extraction is the concern that conventional extraction methods require longer extraction times and that the extended application of a high temperature may result in the thermal degradation of Danshen's constituents. Table 4 provides extraction yields for the same sample of Danshen from Figure 18 using three conventional benchtop heat-reflux extraction (HRE) methods.
|salvianolic acid A||0.435||0.437||0.454|
The solvent for HRE-1 is 80% methanol and 20% water (by volume) with the extraction carried out twice for 60 min each. For HRE-2 the solvent is 100% methanol, with a single 60 min extraction. The solvent for HRE-3 is 75% methanol and 25% water (by volume), with a single 60 min extraction. The temperature for each extraction is the solvent’s boiling point.
Compare your results from Investigation 31 with the results reported in Table 4. Do these results support a concern that heat-reflux extractions may distort the apparent composition of Danshen? As you consider this question, you may wish to review the chemical structures of these compounds, which are shown in Part I, and the HPLC data in Figure 19 for samples drawn at different times during an extended heat-reflux extraction of Danshen.