Thermo Fisher Scientific has developed an accurate and reproducible high-performance liquid chromatography (HPLC) method for the single-injection determination of tolterodine and tartrate—the active pharmaceutical ingredient (API) and its counterion—in an encapsulated drug product containing tolterodine tartrate. Application Note 1047: Simultaneous Determination of Tartaric Acid and Tolterodine in Tolterodine Tartrate demonstrates that this method requires only 13 minutes per analysis. This new approach uses a trimode silica-based column and a detector that is ideal for the determination of counterions, many of which lack a chromophore.

Pharmaceutical companies must ensure that a drug product contains the appropriate amount of its API. This is typically validated with an HPLC-based assay. Many APIs are paired with a counterion to form the drug substance. With knowledge of the ratio of API to counterion, the API amount in both a drug substance and a drug product can be checked by assaying the counterion. In this assay the API can be determined and checked, by determination of the counterion, in a single sample injection.

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