Glass capillary positive preparation refers to the treatment of glass capillaries to form positive charges on their surface, thereby increasing the interaction force between their surface and the sample. It is commonly used in chromatographic separation, capillary electrophoresis, and other scientific experiments. The formation of positive charges is usually achieved by forming a cationic layer on the surface of a glass tube. The following is a brief description of the method and related equipment for preparing glass capillary positivity:
1. Common methods for preparing glass capillary positive samples
(1) Surface chemical treatment method
This method involves chemically treating the surface of a glass tube to give it a positive charge. Common surface chemical treatment methods include:
Ammonia treatment method: Using ammonia gas (NH3) to treat glass capillaries can generate amino (- NH ₂) groups on the surface of the glass tube. Amino groups can carry positive charges in aqueous solutions, thus forming positive surfaces. This method is commonly used in chromatography and capillary electrophoresis.
Hydrofluoric acid treatment method: After etching the surface of the glass tube with hydrofluoric acid, a layer of siloxane will be formed on the surface, which will be further treated with ammonia gas or other chemical substances to enhance the positive charge characteristics. This method can not only improve the surface properties of glass tubes, but also increase their hydrophilicity.
Alkylation treatment method: Through alkylation reaction, alkyl groups (such as methyl and ethyl) are clustered on the surface of glass, and these alkyl groups can effectively increase the positive charge density of the glass surface.
(2) Electrochemical method
Electrochemical methods apply a positive charge to the surface of glass through the action of an electric current. Common electrochemical methods include:
Anodizing method: Connect a glass capillary tube to an electrolyte, and form an anodized layer after being electrified. This layer can carry a certain positive charge, enhancing the capillary's adsorption of ions.
Electrolysis method: Positive charges are generated on the surface of glass tubes through electrolytic reactions. This method can form a cationic layer on the surface of the glass tube, which enhances the interaction with the sample.
(3) Plasma processing method
Plasma treatment uses gas plasma to alter the chemical properties of glass surfaces. Usually, gases such as nitrogen and oxygen are used to form positively charged groups on the surface of glass through low-temperature plasma gas. This method is easy to operate and effective, and is commonly used for processing large quantities of glass capillaries.
(4) Self-assembled monolayer method
Self assembling monolayer (SAM) technology uses chemical adsorption to self assemble molecules onto the surface of glass, forming an ordered membrane layer. The formation of positive charges on glass surfaces can be achieved by selecting molecules with positive functional groups, such as quaternary ammonium salt molecules. The self-assembled monolayer method has good uniformity and stability.
2. Device for glass capillary positive preparation
In order to achieve positive preparation of glass capillaries, specialized devices and equipment are usually required. The following are common devices and their functions:
(1) Chemical treatment equipment
Ventilation device: used to uniformly introduce gases such as ammonia, oxygen, hydrofluoric acid, etc. into the interior of glass capillaries to achieve surface treatment effect. Usually, devices such as ventilation pipes, flow meters, and pressure regulating valves are used to control gas flow and pressure.
Chemical reaction tank: used for soaking treatment of glass capillaries. Specific chemical solutions (such as ammonia water, hydrofluoric acid solution, etc.) are placed in the reaction tank, and the desired surface treatment effect is achieved through soaking or stirring.
(2) Electrochemical treatment device
Electrolytic cell: used to place glass capillaries in the electrolyte and perform anodizing or electrolytic treatment by applying an external current. Electrolytic cells are usually equipped with power sources, heating devices, stirring devices, etc.
Power supply equipment: used to provide stable current and voltage, control the rate and effect of electrolysis process.
(3) Plasma processing equipment
Plasma reaction chamber: used to accommodate glass capillaries and perform plasma treatment on them. A gas flow control system can be installed in the reaction chamber to control the ratio and flow rate of different gases.
High frequency power supply: A high-frequency power supply used to generate plasma, typically with a frequency of around 13.56MHz. High frequency power supplies excite gas molecules through electromagnetic fields, forming plasma.
Vacuum pump: used to maintain low pressure in the reaction chamber, ensuring effective generation and stability of plasma.
(4) Self assembling monolayer equipment
Soaking tank: used for soaking glass capillary tubes, usually equipped with a temperature control system that can accurately control the temperature to ensure smooth self-assembly process.
Ultrasonic cleaning device: During the processing, it may be necessary to use an ultrasonic cleaning device to remove impurities from the surface of the glass capillary and ensure good adhesion of the self-assembled film.
3. Common operating steps
Prepare glass capillary tube: Clean the glass capillary tube to remove surface impurities and grease, ensuring the treatment effect.
Select processing methods: Choose ammonia treatment, electrolysis treatment, plasma treatment, or self-assembled membrane treatment according to actual needs.
Processing: Process the glass capillary tube according to the selected method to give it a positive charge on its surface.
Testing and validation: Verify the treatment effect by testing surface charge density, surface hydrophilicity, separation performance, and other indicators.
Storage and use: Processed glass capillaries should be used in a timely manner. If not used for a long time, they need to be kept in a suitable environment to prevent surface charge loss.
Through these methods and devices, positive surfaces of glass capillaries can be efficiently prepared, providing strong support for further separation experiments.