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Gas chromatography requires stationary phases that can withstand high temperatures when analyzing complex samples with large molecular weights and excellent thermal stability. This is especially crucial in fields like petroleum analysis, where the separation of long-chain aliphatic hydrocarbons, organometallic compounds such as metalloporphyrins, polymer additives, and even triglycerides in food often demands column temperatures exceeding 325°C.
Chromatograms recorded at 325°C are typically referred to as "normal temperature" chromatograms, while those conducted above this threshold are classified as "high-temperature" chromatograms. In high-temperature applications, the most commonly used stationary phase is hydroxyl-terminated polysiloxane. During the coating process, this material undergoes condensation and crosslinking, and it also reacts with silanol groups on the quartz surface, forming a strong bond with the capillary wall.
Several high-temperature gas-liquid chromatography stationary phases have been developed for advanced applications:
1. A polyimide-coated elastic quartz capillary column, capable of operating between 0°C and 430°C.
2. A PAS (polyamide-imide) metal-coated elastic quartz capillary column, suitable for temperatures ranging from -20°C to 450°C.
3. An aluminum-coated elastic quartz capillary column, which can function within a range of 0°C to 430°C.
4. Another aluminum-coated elastic quartz capillary column, using a polysiloxane-carbonyl-based fixed liquid, with a temperature range of 10°C to 480°C.
5. A polyimide-coated elastic quartz capillary column, designed for use between -20°C and 350°C.
These specialized columns allow for more accurate and efficient separation of challenging compounds under extreme thermal conditions, making them essential tools in modern analytical chemistry.