This application note introduces the analysis of polysiloxane using GPC/SEC with RI and ELS detection on Agilent PLgel 5 µm MIXED-E column. Polysiloxanes are important commercial polymers used in applications such as lubricating oils, defoaming agents, and sealants. Analyzing these materials by gel permeation chromatography (GPC) is an important part of process and quality control procedures. Although polysiloxane is soluble in tetrahydrofuran (THF), it has the same refractive index as this solvent. Therefore, refractive index (RI) detection cannot be used with THF.
Polysiloxanes are important commercial polymers used in various applications such as lubricating oils and sealants. Analyzing these materials via gel permeation chromatography (GPC) is crucial for process and quality control. However, because polysiloxanes are isorefractive with tetrahydrofuran (THF), standard refractive index (RI) detection cannot be used with this solvent.
The document outlines two options for analysis: changing the solvent to use RI detection or using THF with an Agilent evaporative light scattering detector (ELSD). The ELSD provides a positive response proportional to sample concentration in all solvents and does not generate system peaks due to solvent imbalance. The note includes specific conditions for the analysis, including column type, flow rate, and detector settings, and compares the data quality between RI and ELS detection.
| Sample concentration | 0.2% Sw/v |
|---|---|
| Column | 3 x Agilent PLgel 5 pm MIXED-E, 300 mm = 7.5 mm |
| Eluent | Toluene or THF |
| Flow rate | 1.0 mL/min |
| Injection volume | 100 pL |
| Detector Neb temperature | 40 °C |
| Detector Evap temperature | 80 °C |
| Detector Gas flow | 1.0 SLM |
Polysiloxane is isorefractive with the tetrahydrofuran (THF) solvent, making RI detection ineffective.
ELSD does not rely on refractive index, works in all solvents, does not generate system peaks, and offers higher sensitivity.
The ELS sensitivity is about 250 times higher than the RI detector.