Identification and control of impurities in streptomycin sulfate by high-performance liquid chromatography coupled with mass detection and corona charged-aerosol detection

For the control of impurities in streptomycin sulfate a reversed phase ion-pair high performance liquid chromatography (HPLC) method using charged aerosol detection (CAD) was developed. With this method, 21 impurities could be separated and tentatively identified using a combination of exact mass measurement by TOF-MS and MS/MS experiments with a triple quadrupole MS. For three impurities the suggested structures could be confirmed by in situ formation. The CAD detector response was found to be linear over 2 orders of magnitude allowing a straightforward quantification of all impurities. A limit of quantification of 0.09% for streptomycin sulfate and of 0.008% for streptidine sulfate (referred to the concentration of the 5 mg/ml test solution) could be achieved. The HPLC method was applied to the purity testing of 12 samples of commercially available streptomycin sulfate from different manufacturers. Impurity levels between 4.6% and 16.0% were found. The current European Pharmacopoeia monograph for streptomycin sulfate only limits streptomycin B by a TLC test to 3.0%. Therefore, the results of this study underline the importance of introducing a state-of-the-art test for the control of impurities in the monograph. The new HPLC-CAD method is considered suitable for this purpose.