Towards a generic method for ion chromatography/mass spectrometry of low-molecular-weight amines in pharmaceutical drug discovery and development.

RATIONALE: Low-molecular-weight amines are encountered in pharmaceutical analysis, e.g. as reactants in chemical syntheses, but are challenging to analyse using ultrahigh-performance liquid chromatography/mass spectrometry (UHPLC/MS) due to their high polarity causing poor retention. Ion chromatography/mass spectrometry (IC/MS) is an emerging technique for polar molecule analysis that offers better separation. A generic IC/MS method would overcome problems associated with using UHPLC/MS in drug discovery and development environments. METHODS: Amine standards were analysed using IC/MS with gradient elution (variety of column temperatures evaluated). An electrospray ionisation (ESI) quadrupole mass spectrometer was operated in positive ion polarity in scanning mode. The make-up flow composition was evaluated by assessing the performance of a range of organic modifiers (acetonitrile, ethanol, methanol) and additives (acetic acid, formic acid, methanesulfonic acid). The ESI conditions were optimised to minimise adduct formation and promote generation of protonated molecules. RESULTS: The performance attributes were investigated and optimised for low-molecular-weight amine analysis. Organic solvents and acidic additives were evaluated as make-up flow components to promote ESI, with 0.05% acetic acid in ethanol optimal for producing protonated molecules. The hydrogen bonding capability of amines led to abundant protonated molecule-solvent complexes; optimisation of source conditions reduced these, with collision-induced dissociation voltage having a strong effect. The detection limit was ≤1.78 ng for the amines analysed, which is fit-for-purpose for an open-access chemistry environment. CONCLUSIONS: This study demonstrates the value of IC/MS for analysing low-molecular-weight amines. Good chromatographic separation of mixtures was possible without derivatisation. Ionisation efficiency was greatest using a make-up flow of 0.05% acetic acid in ethanol, and optimisation of ESI source conditions promoted protonated molecule generation for easy determination of molecular weight.

Impurity analysis of 2-butynoic acid by ion chromatography-mass spectrometry.

Small organic acids are widely used within the pharmaceutical industry but can be difficult to analyse. Ion chromatography is a suitable technique for the analysis of these acids but method development can be hindered as mass spectrometry is not often used as a detector; this means that peak tracking and peak purity cannot be performed. The authors report method development for the analysis of 2-butynoic acid, where by using electrospray ionisation mass spectrometry, peak purity was investigated and the presence of co-eluting impurities determined. Optimisation of the additives in the make-up flow to the mass spectrometer was shown to have an impact on the response observed. A standard series of organic acids were analysed spiked in to 2-butynoic acid at levels representative of impurities, the presence of the 2-butynoic acid did not impact the linearity or limit of detection observed for the acids; R2 values greater than 0.98 were obtained for all acids with and without the presence of 2-butynoic acid with a limit of detection at 1 ppb for all but one of the acids.