Development of a chemically sensitive online SEC detector based on FTIR spectroscopy

Abstract

Polymer materials are becoming more complex and require increasingly sophisticated analysis methods. The development of coupled techniques, especially SEC and molecular spectroscopy, is one approach to meet this need. In this report, the technical realization of a new FTIR spectroscopy and SEC coupling, where the FTIR serves as a true online detector is described. The basic idea is to measure FTIR spectra online with the highest possible sensitivity and then use a mathematical approach to subtract the solvent signals, reduce drifts and minimize noise. This publication describes in detail how this method was optimized including the most important demands on the spectrometer and other required equipment, e.g. the custom designed flow cells. The applied data treatment, which is called “solvent suppression”, and a guide to interpretation of the data are explained in detail. Several application examples demonstrate not only the potential of the method, but also clarify the current limits. It is shown that FTIR spectroscopy can successfully be used as an online detection method for SEC to provide detailed chemical information as a function of the elution volume, respectively molecular weight, for basically any polymer in any isocratic solvent. It is also shown that minor components down to ca. 5 mol% can be detected.