| Abstract: | A commercially available densitometer, DMA 60 (Anton Paar, Austria), in combination with a Model DMA 602-W flow cell was used as a detector in a Waters Model 200 GPC equipped with differential refractive index and ultraviolet absorbance detectors. The density measuring cell was thermostatted to ±0.004°C and the sample injection concentration was 1.5 mg/mL. Polystyrene samples of molecular weights ranging from 9000 to 860,000 were used. The optimum period was found to be 10,000 oscillations, a setting which gave good resolution and a sufficient number of data points to define the chromatogram. The molecular weight averages calculated using the density outputs compared well with those obtained through the conventional UV detector. A sliding average technique was applied to the densitometer data for reducing the baseline noise. It was found that concentrations as low as 1.0 mg/mL (≈0.114%) could be used to obtain densitometer chromatograms that yield molecular weight averages comparable to those obtained from the ultraviolet detector. This densitometer thus appears suitable to be used as an additional GPC detector for routine analyses. |
