Impurity profiling of l-methionine by HPLC on a mixed mode column

• Impurities of methionine have been synthesized.
• HPLC method for impurity profiling in methionine has been developed and validated.
• Application of mixed mode chromatography.
• The content of impurities in batches was found to be very low.

Methionine is mostly produced synthetically. Thus, impurities are synthesis by-products in addition to oxidation and dimerization products. Here, a sensitive HPLC method for the determination of impurities in l-methionine was developed and validated using a SIELC® Primesep 100 column. Impurities were separated on the mixed mode column by reversed phase and cationic exchange mechanism. The limit of detection was in the range of 0.06–0.30 μg/ml (0.0004–0.002%), limit of quantification in the range of 0.30–0.75 μg/ml (0.002–0.005%) and linearity was shown in the range of 0.3–30.0 μg/ml (0.002–0.200%). The method was found to be precise (intermediate precision RS <5%; n = 2) and accurate (recovery 96.0–121.4%, n = 3). The method is also suitable for the purity assessment of dl-methionine and d-methionine. The amount of impurities found in batches was very low. Only l-methionine-sulfoxide and N-acetyl-dl-methionine could be detected in levels less than 0.05%.

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