Benefits of using mass detection for analysis of non-chromophoric compounds

The development of chromatographic methods for natural products and pharmaceuticals can be challenging for many reasons. These challenges can include poor or no UV absorbance, or similar UV spectra among components. For components that exhibit poor or no UV absorbance, practitioners typically explore alternative modes of detection such as FLR and evaporative light scattering (ELS). In this work, we will present a method for analyzing the non-UV absorbing active pharmaceutical ingredient memantine HCl and its associated metabolites. We will use a compact mass detector to efficiently track these components during the method development. We will demonstrate the linearity, reproducibility, and specificity achievable with mass detection.

Components of the sample were identified and tracked by mass detection over the method development runs. For final UPLC method, we selected low pH (125 mM formic acid in water), CORTECS C₁₈₊ column at 45 °C, and gradient of 5 – 90% with acetonitrile over 5 minutes. Flow rate and injection volume were set to 0.6 mL/min and 1.0µL, respectively.

Memantine HCl and its associated metabolites do not absorb in UV as they lack chromophore but ionize well and are detectable by MS. To demonstrate that MS detection is suitable for analysis of these compounds, we tested the developed method for linearity, reproducibility, and specificity. Linearity show good correlation between peak responses and concentrations with correlation coefficient (r²) greater than 0.999 for each component. System suitability results of 5 replicate injections were evaluated and compared with the USP specifications. The developed UPLC method was applied for memantine HCl assay in the tablet formulation.

In summary, mass detection enabled accurate identification and tracking of non-UV absorbing components during the method development process. Reproducibility and linearity of the developed UPLC/MS method was excellent.