Siloxanes are currently the mainstay of gas chromatography stationary liquids

Although there are over a thousand types of gas chromatography stationary liquids that have been used and studied to meet the requirements of low column efficiency and high selectivity in packed columns, however, for modern capillary chromatography columns, these stationary liquids are rarely used in combination.Among them, almost all the ones that can still be used in capillary chromatography columns are polysiloxanes, except for polyethylene glycol. Therefore, in the synthesis of new stationary liquids, it is still limited to using polysiloxane as the backbone and introducing different selective groups. This is because polysiloxane based stationary liquids have the following advantages: (1)Good thermal stability; (2)Good film-forming performance; (3)Low glass transition temperature and wide temperature range for use; (4)If there is a certain amount of vinyl group in the molecule, it is easy to crosslink;(5)Good diffusion performance, low mass transfer resistance, and easy to achieve high column efficiency; (6)Various organic molecular fragments can be introduced on the side chains of polysiloxane to regulate selectivity. Since the 1970s, a series of excellent gas chromatography stationary liquids have been developed based on polysiloxane based stationary liquids.

stationary liquids with good thermal stability

At present, many high boiling point complex mixtures require the use of high-temperature resistant capillary chromatography columns, such as hydrocarbons with a carbon number of up to 100 in petroleum, triglycerides in food, six and seven ring polycyclic aromatic hydrocarbons in environmental pollutants, all require stationary liquids with excellent thermal stability. Almost none of the stationary liquids used in the past were able to withstand high temperatures of 370℃. Therefore, in recent years, some capillary column stationary liquids that can be used at around 400℃ have emerged.

(1) polydimethylsiloxane with high temperature resistance

Someone used a capillary column coated with polydimethylsiloxane to separate hydrocarbons with a carbon number of 90 at 390℃. Heating to 430℃ by a program can cause hydrocarbons with 100-110 carbon atoms to flow out of the chromatographic column. A few years ago, VIBI company used a narrow distribution of polydimethylsiloxane (Unimolecular Low Bleed VB-1), its characteristic is to purify the prepolymer and remove oligomers, polysiloxane chains have branched chains, reducing crosslinking dose, using the principle of complete cross-linking, the end groups are also incorporated to form a network as a whole, but no low molecular weight compounds.

(2) Choosing cross-linked polysiloxane stationary liquids to improve its thermal stability

In situ crosslinking (solidification) in capillary columns is an important way to improve the stability of liquid films, it is also a necessary way of preparing anti solvent washing. Some polymethylsiloxanes with high phenyl content, such as OV-17, OV-25, and OV-225, are difficult to crosslink with initiators, but they can be crosslinked by introducing a certain amount of vinyl group, so when studying stationary liquids for capillary chromatography, ethylene groups are introduced into the stationary liquids molecules or hydroxyl terminated polysiloxane stationary liquids are used.

(3) Improving thermal stability by using siloxane/silyaryl copolymer

If the oxygen atom in the main chain of polysiloxane is replaced with phenylene, its thermal stability will be improved, these compounds can withstand high temperatures when used as gas chromatography stationary liquids. According to the research results of Buijten et al., high-performance capillary columns can be coated with such compounds, with a coating efficiency of 102%. This chromatographic column can separate polycyclic aromatic hydrocarbons at 370 ℃

(4) Leading borane into the polysiloxane chain to improve thermal stability

Leading decaborane into the siloxane chain can improve the heat resistance of the fixed solution, now there is information online showing that Beijing Green Herb Technology provides Dexsil 300 GC as a stationary phase, this stationary phase is mainly used for drugs, triglycerides and ethers, high boiling aliphatic hydrocarbons, high boiling hydrocarbons, steroid compounds, insecticides, and sugars.