Fourier transform infrared spectroscopy with a sample deposition interface as a quantitative detector in size-exclusion chromatography

The use of a state-of-the-art commercial solvent-elimination interface for liquid chromatography–infrared spectroscopy is discussed from the perspective of quantitative analysis. The effect of eluent flow-rate is investigated with respect to the homogeneity of the deposit and the trace width along the deposition trace. Low flow-rates (50 μl/min or less) turn out to be favorable for obtaining a good trace and a high sensitivity. The trace width decreased from 2.20 to 1.13 mm when the flow-rate was reduced from 500 to 25 μl/min. Preservation of chromatographic detail during deposition was evaluated at different substrate moving speeds. The additional (extra-column) band broadening that is inherent to nebulizer-deposition interfaces, causes a loss in resolution in size-exclusion chromatography (SEC)–Fourier transform infrared (FTIR) spectroscopy in comparison with SEC–UV. The repeatability of the deposition is evaluated by SEC–FTIR analyses of polystyrene standards (peak molar-masses: 1250–2 950 000 g/mol) and the RSD is found to range from 3.2 to 5.8% in response and from 0.21 to 0.47% in retention time.