Preparation of Pharmaceutical Samples for Metals Analysis

There has been a lot of discussion regarding the methods of analysis for pharmaceutical products as we await the upcoming changes to both the EP and USP, relating to the analysis of metal impurities.

The USP chapter <233> currently offers two compendial techniques for the analysis of these impurities; Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). These techniques are also referred to in the EP section on metal residues, along with several other techniques.

The relative virtues of ICP-MS and ICP-OES have been frequently discussed, especially with respect to detection and specificity parameters. However, sample preparation is often overlooked as an important aspect of the analysis of pharmaceutical samples. After all, if the sample is not prepared properly, any subsequent analysis will be compromised. Both the EP and USP do cover aspects of sample preparation, but not in any great detail. The EP gives guidance as to whether a sample is suitable for analysis by following a flow chart whereas the USP lists four techniques for preparation, namely direct analysis, dissolution in aqueous, dissolution in organic solvents, or closed vessel digestion. Each of these techniques has its own advantages and disadvantages.

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