[Reliability of sulfur dioxide determination method documented in Chinese pharmacopoeia for evaluating Paeoniae Radix...

The content of SO2 in Paeoniae Radix Alba (RPA) was determined by the method documented in Chinese Pharmacopoeia (CP) 2010 edition to validate the repeatability of the method for evaluating RPA, and the contents of paeoniflorin sulfonate in both the residual material and distilled solution of RPA were determined by HPLC to study the transformation of paeoniflorin sulfonate to SO2 by HCl. It was found that the repeatability of the method in CP for evaluating RPA is unacceptable, and paeoniflorin sulfonate was detectable in both the residual material and distilled solution of RPA even at "the end point" of SO2 determination, merely about 50% of paeoniflorin sulfonate was transformed to SO2 by HCl, indicating that the current SO2 determination method in CP is not able to accurately quantify SO2 in RPA. It is recommended that more special method for determining SO2 content in RPA should be developed regarding the chemical characteristics of sulfur-fumigated RPA.