Digestion of Difficult APIs and Gel Capsules in Accordance with USP <233>

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The new USP Chapters <232> and <233> will become official on January 1, 2018. At that time, they will supersede the current Method <231>, which will no longer be valid. These new methods bring significant changes in sample preparation and analysis of pharmaceutical samples both in excipients and API’s. Certain APIs pose challenges to traditional microwave digestion methods as they are very stable compounds and not easily broken down.

CEM recently introduced the iPrep vessel with a patented dual-seal technology that allows the vessel to hold much higher temperatures and pressures than typical digestion vessels. Digestion of difficult API’s and large gelatin capsules was achieved using this vessel and iWave advanced temperature control.



The new USP Methods <232> and <233> call for total digestion of pharmaceutical samples and quantification of individual elements typically by ICP-OES or ICP-MS analysis. Many pharmaceutical materials can be easily digested but APIs with multiple aromatic ring structures can be very difficult to completely break down and obtain a clear digestion, as prescribed in the new chapters. In addition, large gelatin capsules can prove challenging because of the amount of oil they typically contain. A large amount of gas is released once the capsule is dissolved and the acids begin to attack the contained oil which can lead to loss of volatile elements if not properly contained.

This application note will focus on the use of the CEM MARS 6 microwave digestion system with iPrep vessels to completely digest both difficult active pharmaceutical ingredients and large gelatin capsules. Sample structures of APIs are shown to illustrate complexity. Sample sizes are given as maximum allowable to achieve clear digest.