Positive and negative electrospray ionisation travelling wave ion mobility mass spectrometry and low-energy collision-induced dissociation of sialic acid derivatives.

Mono- or oligosaccharide-containing samples, whether they are derived from biological sources or products of chemical synthesis, are often mixtures of spatial or constitutional isomers. The possibility of characterising or performing quality control on such samples by mass spectrometry is hampered because these isomers cannot be separated by their mass-to-charge ratio alone. Therefore, the use of techniques to separate the isobaric sample compounds prior to mass spectrometric characterisation is mandatory. Travelling wave ion mobility separation offers the possibility of separating mixtures based on their compound's collisional cross-sections in the gas phase and can easily be combined with mass spectrometry for further characterisation. Here, we use 5-N-acetylneuraminic acid and several derivatives as model compounds to evaluate the separation power of travelling wave ion mobility spectrometry and present an approach to clearly identify constitutional isomers in mixtures in combination with low-energy collision-induced dissociation (CID) in the negative ion mode even if they cannot be completely separated by ion mobility.