Compositional separation and detection

One possible solution to the above problem is to fractionate the polymer using preparative-scale SEC, then examine the fractions with powerful off-line techniques such as mass spectrometry, Fourier transform infrared and nuclear magnetic resonance. This technique can also be used to isolate pure polymer fractions for subsequent use in SEC calibration. 

The combination of these two powerful characterisation techniques can provide the ability simultaneously to characterise the molecular distribution and to identify and quantify IR-active functional groups in the distribution. The main problem in linking such technologies is the choice of solvent or eluent used to carry the polymer through the SEC system. Many of the typical SEC solvents have strong absorption bands in wide regions of the infrared spectrum. Developments have centred around the use of low-volume cylindrical internal-reflection flow cells for use in the FTIR system. However, their use is still restricted in many cases to IR-friendly SEC solvents. 

A second approach, recently commercialised, spray-deposits the eluent from the chromatograph on to a moving collection surface (germanium disc). The solvent is then evaporated in the deposition process, and the polymer is deposited as a dry track. This disc can then be physically taken and scanned in an FTIR spectrophotometer and spectra in the various regions of the chromatogram can be collected. By using the approaches described in this section 

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