Part VII. Verifying the Analytical Method's Accuracy

Investigation 32: Comparing Results to Other Analytical Methods

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.

Table 4 Extraction Yields (mg/g) Using Conventional Methods
analyte HRE-1 HRE-2 HRE-3
danshensu 1.618 0.826 1.052
rosmarinic acid 2.032 2.016 1.619
lithospermic acid 2.675 1,785 2.265
salvianolic acid A 0.435 0.437 0.454
dihydrotanshinone 0.352 0.354 0.295
cryptotanshinone 0.571 0.599 0.543
tanshinone I 0.913 0.982 0.926
tanshinone IIA 1.952 2.280 1.738

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.

Investigation 32. 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.