We have developed a Reversed-Phase (RP) UV- HPLC chromatography method. It is used for stability studies of our new pharmaceutical protein.
How do we identify the peaks observed by UV to confirm they are product-related impurities? Can we ensure that UV-peaks contain single molecules?
The best way I know of is to connect the HPLC directly to a mass spectrometer (LC-MS). This provides a simple characterization of peaks observed by UV-HPLC. By doing this, you have an additional detection method that can distinguish molecules by their molecular mass – which is perfect for stability studies .
You probabably already know that sometimes it is not possible to separate degradation products by RP chromatography alone. However, combining HPLC analysis and LC-MS analysis makes it quite easy to use molar mass to identify degradation products. For example deamidations, oxidation, and truncated molecules .
Another benefit I’d like to highlight of combining HPLC analysis and Mass Spectrometry analysis is that you can confirm that single peaks only contain one molecule [1-3].
The problems of using Reversed-Phase HPLC analysis with UV detection alone are:
- It is not always possible to separate the drug substance (DS) from product-related impurities .
- You might see a shoulder. But you have no way of knowing if it is an artifact or a DS related molecule (degradation product).
- New peaks appearing in the chromatogram cannot be characterized directly by UV detection .
Fortunately, there’s a simple solution
Coupling an HPLC instrument directly to a high-resolution mass spectrometer provides you with an additional detection level for product-related impurities [1-3].
Reversed-phase chromatography typically uses buffers that are directly compatible with mass spectrometry. Therefore it is quite straight-forward to connect the two instruments [1-3].
So when should you use LC-MS analysis in stability studies?
You can apply LC-MS analysis to all types of biomolecules. Hence, both synthetic peptides, recombinant proteins and antibodies. Therefore, I suggest you use the analysis to confirm product-related impurities whenever your chromatogram shows an unexpected peak [1, 3].
In most cases, you will find that the LC-MS signal is much more sensitive than UV detection. In addition, you will see that the accuracy of MW determination for all types of molecules is in the low ppm range.
This enables confident identification of the molecule.
 Barbarin et al: “Comparison between liquid chromatography-UV detection and liquid chromatography-mass spectrometry for the characterization of impurities and/or degradants present in trimethoprim tablets.“, Journal of Chromatography A, 2002
 Gillespie et al: “Mass spectrometry for small molecule pharmaceutical product development: A review“, Mass Spectrometry Reviews, 2011
 Chen et al: “Applications of LC/MS in structure identifications of small molecules and proteins in drug discovery“, Journal of Mass Spectrometry, 2007