Hi, I am currently developing an LC-HRMS method for the analysis of an NDSRI in a powder-for-injection formulation. The compound belongs to the penem class.
For sample preparation, I am using water as the diluent. During mass spectrum interpretation, particularly while selecting the quantifier ion, I observed that the parent ion in the sample shows a relatively higher mass error (~6–7 ppm), though it is still within the acceptance limit (±10 ppm). In contrast, the NDSRI reference standard exhibits a much lower mass error (~1 ppm).
Based on prior experience, I initially suspected a matrix effect. However, the formulation contains only a single excipient—sodium carbonate—which makes the situation less straightforward.
I would appreciate your insights or suggestions on possible causes for this observation. @Phil @Naiffer_Host