Filter-based infrared detectors for high temperature size exclusion chromatography analysis of polyolefins: Calibration with a small number of standards and error analysis

Infrared detection has been shown to be very appropriate for high temperature analysis of polyolefins. After some early reports in which dispersive or single-band filter-based detectors were applied, Fourier transform detectors have been described for this application, in order to improve the method sensitivity. Modern simple filter-based detectors prove, however, comparable sensitivity while providing a number of practical advantages when coupled to chromatographic systems: reduced cell volume, simplified hardware, continuous generation of absorbance chromatograms, as well as simpler data collection and processing. A practical method for calibration, using multiple-band signals obtained with filter-based detectors and a small number of reference materials, is here discussed. Calibration data are used to compare the performance of detectors based on different opto-electronic technologies and filter designs. A procedure for estimation of errors in the slice-by-slice measured methyl frequency, based on signal-to-noise ratio considerations, is described. The good accuracy provided by the filter-based IR detectors was noticeable, considering that it was obtained using a small set of reference materials. A minimal concentration of 0.009 mg/mL was estimated to be required at the detector cell, in order to keep the errors below one unit of methyl per one thousand total carbons. This low minimal concentration requirement allows using standard SEC conditions, without compromising the molar mass distribution accuracy and resolution.