Characterisation of fluorinated copolymers using liquid chromatography coupled on-line to mass spectrometry, with automated data interpretation

Abstract

A perfluorinated co-polyether was characterised in terms of the number and type of functional end groups present on the molecule. The polymer was separated chromatographically according to the polarity of the polymer end groups and the separation was coupled on-line to an electrospray ionisation time-of-flight mass spectrometer. Negative-mode electrospray ionisation of the relatively non-polar polymer was achieved by post-column addition of a polar constituent to the mobile phase. LC–MS analysis of polydisperse analytes is a highly data intensive technique and manual interpretation of the resulting data can be extremely complicated, especially for the characterisation of copolymers or polymers with end-group distributions. In order to overcome this problem, an automated data-analysis program was developed that allows the user to quickly determine the probability of the presence of a certain molecular compound. The program evaluated data in terms of the possible combinations of monomeric units and end groups that could be combined to make up the mass values present in the mass spectra. Using the program, the polymer can be characterised according to its molar-mass, chemical-composition and functionality-type distributions. A graphical representation of the LC–MS analyses is presented to give a clear overview of the two-dimensional separation. The identification of various end groups on the polymer is also presented graphically, as (a) a histogram (frequency of matches versus time), (b) a two-dimensional plot (masses that match the particular end group combination versus LC retention time) and (c) a plot of average chemical composition versus LC retention time.