MIC for Reaching Lowest Element Concentrations for Pharmaceuticals

For the determination of ultra-trace concentrations of elemental impurities Microwave-induced oxygen combustion (MIC) represents a valuable option to deal with the given quantification limits of ICP-OES and ICP-MS analysis


USP chapter <233> Elemental Impurities-Procedures describes enhanced sample preparation procedures prior to measurement with high-quality instrumentbased analytical techniques (ICP-OES and ICP-MS). Microwave-assisted acid digestion is already mentioned as potential sample preparation technique in this chapter. Since acid digestion is performed with concentrated acids and ICP analyses suffer under significant signal suppression in combination with high acid concentrations dilution steps of the digestion solutions are required.

Hence for samples with a very low impurity load it could be difficult to exceed the quantification limit of the ICP.

For such cases MIC can be a powerful alternative due to the usage of diluted acids which makes it possible to directly introduce the digestion solution to the measuring system. Besides, minimized residual carbon contents have a positive impact on the analysis of these samples.

MIC combines the advantages of the ashing combustion technique and closed-vessel acid digestion in one system. The combustion of the samples is triggered by microwave radiation in an oxygen-pressurized quartz vessel. In the subsequent reflux step microwave irradiation is applied to generate conditions for digesting residues and recovering analytes in the presence of an absorbing solution.

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