Key Predictive Sample Set KPSS

Counter-ions, usually small polar or ionic compounds, are routinely used to enhance the aqueous solubility and/or stability of the API. Because of their polarity, counter-ions are rarely resolved from the chromatographic solvent front in reversed-phase HPLC and have characteristically poor chromophores which makes detection difficult. The counter-ion can be omitted from the achiral method development sample set with minimal risk when this holds true. Analysis of counter-ions is normally performed using ion chromatography.9,10 This assay is separate from the reversed-phase assay performed to measure organic impurity levels. 

Note Benzoate, besylate, and tosylate salts are examples of counter-ions that are sufficiently retained and should be included in the method development set. 

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Selection of key predictive sample set (KPSS) for analytical method development... 

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