Electrospray mass spectrometry as online detector for low molecular weight polymer separations with flow field-flow fractionation

By coupling flow field-flow fractionation online to a high resolution mass spectrometer with electrospray ionisation, it was possible to separate low molecular weight polymers and to obtain mass chromatograms for specific polymers. Problems involved and their solutions in combining the mass spectrometer with field-flow fractionation are discussed. Separation efficiencies were tested for polystyrene sulphonates with different carrier solutions, and it was found that the ionic strength had to exceed about 20 mmol L-1 in order to achieve good separation. Salt clusters are formed in the electrospray interface at high ionic strengths, giving rise to a background in the mass spectra and it was found that the composition of the carrier solution and the tuning of the instrument were crucial to the signal to noise ratio. It was also found that, by adding a second electrolyte to the carrier solution, the extent of cluster formation was decreased.