Chromatography focus on
High-Speed, High-Resolution Analysis of Low Molecular Weight Polymers Using the Advanced Polymer Chromatography (APC) System
Mia Summers and Michael O’Leary Waters Corporation, Milford, MA, USA
Gel permeation chromatography (GPC) is a well-established, informative method for characterising polymers. However, while a great amount of information can be obtained using this technique, there are inherent limitations to this type of analysis. Columns are frequently styrene-divinylbenzene based and require proper conditioning as well as operation under low back pressures to ensure long-term stability. Particles are typically larger (≥5µm) and resolution is often compromised as a result. Smaller particle (<5µm) columns are commercially available and improve the speed of GPC separations, but the speed is limited by their inherently low maximum operating pressures. In addition, the large system volumes of conventional GPC instrumentation require the use of large diameter columns to mitigate the system bandspreading, which can lead to a deterioration in resolution. Waters ACQUITY Advanced Polymer Chromatography (APC) System combines sub 3-µm hybrid particle columns, enhanced system stability, and the capability of accurate flow rates at higher pressures. Additionally, the low overall system dispersion can significantly affect resolution, especially for low molecular weight oligomers. Improved resolution in low molecular weight oligomer separations with shortened runtimes enables rapid monitoring of polymer process development, earlier detection of new polymeric species, and altogether faster commercialisation of new polymer products.
In this application note, separations using the ACQUITY APC System will be compared to conventional GPC separations. Faster analysis, improved resolution, and the beneficial effect on calibration of low molecular weight oligomers using a low-dispersion system with sub 3-µm hybrid particle technology columns will be illustrated. The combination of these technologies allows more robust and precise determination of molecular weight parameters for low molecular weight polymer samples. Earlier identification of even subtle changes in a polymer can significantly speed up the development of polymers for chemical and biomaterial applications.
Results and Discussion
To properly characterise polymers using SEC, it is important to generate a calibration curve using appropriate standards to establish the separation range with the columns being used. With long conventional GPC run times of up to one hour (or more), analyses of standards and samples can be quite time-consuming. Since the data generated for samples will be compared against the calibrated standards to determine molecular weight, the accuracy of the standard results is paramount in order to obtain accurate results for the polymer sample. In addition to the long run times inherent in GPC, the large extra-column volume of conventional GPC systems can result in peak bandspreading, reducing the resolution and thus accuracy of the calibration points. The lower dispersion ACQUITY APC System, delivers less bandspreading and the narrow standard peaks are much sharper, compared to the conventional GPC system, as shown in Figure 1. Additionally, combining the low-dispersion of the APC System with robust sub 3-µm APC Column Technology that supports higher flow rate and backpressures also improves resolution for the 1K polystyrene standard, and provides a five-fold reduction in analysis time.
25 30 35
10 15 20
0 5
13.0 14.0 15.0 16.0 17.0 18.0 19.0 20.0 21.0 22.0 23.0 24.0 25.0 26 Minutes
-1.0 0.0 1.0 2.0 3.0 4.0
1K Polystyrene standard
Conventional GPC 3 x Styragel 7.8 x 300 mm
10 12 14 16 18 20
0 2 4 6 8
2.00 2.20 2.40 2.60 2.80 3.00 3.20 3.40 3.60 3.80 4.00 4.20 4.40 4.7 Minutes
0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8
20.0 20.5 21.0 21.5 22.0 22.5 23.0 23.5 24.0 24.5 25.0 25.5 26.0 Minutes
1K Polystyrene standard
ACQUITY APC System 3 x APC 4.6 x 150 mm
3.70 3.80 3.90 4.00 4.10 4.20 4.30 4.40 4.50 4.60 4.70 Minutes
Figure 1. A comparison of run times and resolution for polystyrene standards (Mp: 100K, 10K, and 1K) on a conventional GPC system and the ACQUITY APC System.
MV
MV
100K 10K
1K
µRIU
µRIU
100K
10K
1K
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