How Mass Spectrometry Imaging Contributes to Pharmaceutical Quality Control: The ‘Molecular Fingerprint’ Within Tablets

There is a classic challenge in pharmaceutical quality control: even if a sample is found to be ‘within specification’ following analysis, this does not necessarily mean that the entire tablet is compliant. Traditional methods involve taking several samples from a tablet, homogenising them and analysing the mixture to obtain an average value; however, if the active pharmaceutical ingredient (API) is unevenly distributed within the tablet, or if agglomeration or stratification occurs, the average value is likely to mask these issues. Mass spectrometry imaging provides a complementary approach that offers a view of the entire tablet.

Application 1: Verification of uniform active ingredient distribution

By directly imaging a tablet cross-section, selecting the m/z corresponding to the API, and mapping the signal intensity as colour, one can visualise the distribution pattern of the active ingredient across the entire tablet: uniform distribution indicates that the mixing process has been carried out correctly; if localised variations in concentration are observed, this suggests potential issues in the mixing or tableting stages.

Neo Source INSTRUMENT’s MSI DPI (20–200 μm) is sufficient for observing uniformity at the tablet scale; for finer interlayer or particle-level distribution, the 2–3 μm MSI LDPI provides greater spatial detail. Both can be integrated as standalone imaging sources with users’ existing Agilent, AB SCIEX or Thermo mass spectrometers, eliminating the need to purchase a separate instrument for this specific analysis.

Application Area 2: Spatial Comparison of Innovator and Generic Formulations

In formulation research or as part of the supporting work for bioequivalence studies, imaging can be used to compare whether the spatial distribution of the API and key excipients in the innovator and generic formulations is consistent. Whilst traditional dissolution profiles compare ‘how much is released over time’, imaging compares ‘how it is distributed spatially’ – the two dimensions are complementary.

It is important to clarify the scope: this type of imaging currently serves primarily research, process development and quality control method research; the conclusions are used to improve processes and design, rather than to replace statutory release testing.

Why is the photoionisation approach attracting attention in pharmaceutical applications?

Tablets contain not only the API but also a large number of excipients, polymers and lubricants, resulting in a diverse range of molecular types. Imaging sources centred on photoionisation have a broad applicability to neutral molecules and produce few fragments, which facilitates the ‘identification’ of target molecules within complex matrices; post-photoionisation (secondary photoionisation) further amplifies weak signals by 1–3 orders of magnitude, making it particularly useful for tracer components at low doses and concentrations.

Three key considerations for implementation

• Data management: High-resolution imaging generates gigabytes of ‘pixel × m/z’ data in a single run; storage and pre-processing must be planned in advance.

• Throughput considerations: Point-by-point scanning is inherently slow; for batch quality control, the time required per sample must be assessed to ensure it is acceptable.

• Compliance considerations: Whilst its value as a research tool is clear, method validation, reproducibility and standards remain essential before it can be incorporated into formal quality control workflows.

Overall, the role of mass spectrometry imaging in the pharmaceutical sector is more akin to that of a ‘microscopic imaging device in a quality control laboratory’: whilst it does not replace existing testing methods, it fills a critical gap in the dimensions of ‘uniformity’ and ‘spatial consistency’—aspects that traditional methods cannot clearly assess.