Octadecyl silicone bonded silica thin layer plate (usually referred to as C18 bonded silica thin layer plate) is an important chromatographic analysis tool. The following technical explanations are provided from the aspects of preparation, performance, and application:
1、 Preparation technology
Preparation of silicone substrate:
Silicone, as a substrate material, needs to be polymerized to form nano-sized particles, which are then calcined to form a Si-O-Si network structure, enhancing its mechanical strength and pressure resistance.
The particle size and specific surface area of silica gel particles need to be strictly controlled, for example, using silica gel particles with a particle size of 5 μ m and a specific surface area of 300m ²/g to ensure chromatographic separation efficiency.
Bonding reaction:
Reflux the silica gel with octadecyltrichlorosilane (ODS) in anhydrous toluene to generate octadecyltrichlorosilane bonded silica gel.
The reaction needs to be carried out under nitrogen protection, such as adding pyridine as a catalyst, refluxing for 20 hours, cooling, filtering, washing, and drying under vacuum conditions.
End sealing processing:
To reduce the interference of unreacted silanol groups, small volume methyl or ethyl groups are used for end capping treatment.
The capping reaction needs to be carried out under anhydrous conditions, such as using trimethylchlorosilane or triethylchlorosilane as capping reagents.
2、 Performance characteristics
Hydrophobicity and selectivity:
The introduction of octadecyl chains significantly enhances the hydrophobicity of silica gel, making it suitable for reverse phase chromatography separation.
The hydrophobicity of the bonded phase can be optimized by adjusting the length of the alkyl chain and the degree of silanization, for example, C18 bonds have excellent separation effects compared to alkaline compounds.
Stability and reproducibility:
The chemical bonding phase is not affected by humidity, avoiding the problem of reduced activity caused by moisture adsorption in traditional silicone thin layer plates.
The bonded phase thin layer plate can be reused, for example, it can be regenerated by washing with methanol or dichloromethane and drying.
Chromatographic performance:
The high-efficiency thin-layer plate uses fine-grained silica gel (such as 5 μ m), which significantly improves separation efficiency, development speed, and detection sensitivity.
The theoretical number of boards can reach over 6000, and the separation time can be shortened to 1/10 of that of ordinary silicone boards.
3、 Application Fields
Drug analysis:
Used for the separation of acidic or neutral compounds such as phenols, aldehydes, alkaloids, steroids, and amino acids.
For example, when using C18 bonded silica gel thin layer plates to separate alkaline compounds, the separation effect can be optimized by adjusting the proportion of methanol in the mobile phase.
Organic synthesis monitoring:
Used for rapid separation and identification of reaction intermediates and products.
For example, in the synthesis of polycyclic aromatic hydrocarbons, C18 bonded silica gel thin-layer plates can effectively separate compounds such as benzene, biphenyl, and anthracene.
Environmental monitoring:
Used for the separation and analysis of organic pollutants in water and soil.
For example, using reverse phase thin-layer chromatography to separate phenolic or amine mixtures in environmental samples.
4、 Technical parameters and quality control
Particle size and specific surface area:
The particle size of silica gel is usually 5 μ m, with a specific surface area of 300m ²/g, a pore volume of 0.84cc/g, and a pore size of 9.4nm.
Bond density and sealing efficiency:
The bond density can be determined by elemental analysis, for example, the C18 bond density is 3.51 mol/m ².
The sealing efficiency can be evaluated by detecting the intensity changes of the silanol based absorption peak through infrared spectroscopy.
Chromatographic performance testing:
Determine the activity and separation efficiency of thin-layer plates using standard mixtures.