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

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%.