Comprehensive two-dimensional liquid chromatography with on-line Fourier-transform-infrared-spectroscopy detection for the characterization of copolymers.

The on-line coupling of comprehensive two-dimensional liquid chromatography (liquid chromatography x size-exclusion chromatography, LC x SEC) and infrared (IR) spectroscopy has been realized by means of an IR flow cell. The system has been assessed by the functional-group analysis of a series of styrene-methylacrylate (SMA) copolymers with varying styrene content. Ultraviolet (UV) detection was used as a detection technique to verify the detection with IR. The LC x SEC-IR functional-group contour plots (comprehensive chromatograms) obtained for styrene were in agreement with the contour plots constructed from the UV signal. In addition, contour plots can be obtained from non-UV-active groups. One such plot, for the carbonyl-stretching vibration of methylacrylate (MA), is shown. Selective detection of MA proved possible using flow cell IR detection. The combination of the contour plots for styrene and MA allowed a full characterization of the copolymer and it was revealed that the present series of SMA copolymers exhibited homogeneous chemical-composition distributions (CCDs). In addition, commercially available fast-SEC columns have been assessed in this study with respect to their potential to serve as second-dimension separation columns.