10. What principles should be chosen for the column tube material? What kind of material is the commonly used column tube made of?
A: For the column tube material, it should be selected as follows:
1. It should not react with the stationary phase, sample and carrier gas.
2, to be easy to process and shape.
3. The inner wall of the tube should be smooth and the cross section should be evenly rounded. Generally, the shape of the column tube is U-shaped or spiral, and is mostly made of copper, stainless steel, glass, and the like.
11. What should be done with the new column tube (copper or stainless steel tube)?
Answer: The new column tube should be washed with dilute acid or dilute alkali (1:1 hydrochloric acid or sodium hydroxide) to remove dirt such as oil and dirt, then rinse with tap water, then rinse with distilled water to neutral, then use clean air. After purging and drying, it is ready for use.
Twelve, what is the body? What are the requirements for the carrier?
A: The carrier is a porous, chemically inert solid that is used in gas chromatography to support the fixative. There are several requirements for the carrier:
1, the surface area is large, generally should be between 0.5-2 m / g;
2. Chemically inert and thermally stable;
3, have a certain mechanical strength, so that the coating and filling process does not cause crushing;
4, has a proper pore structure, which facilitates rapid mass transfer between the two phases;
5, can be made into uniform spherical particles, which is good for gas phase penetration and filling uniformity;
6, has a good wettability, easy to even distribution of the fixed liquid. It is difficult to fully satisfy the above requirements. In practice, people can only find a carrier with better performance.
Thirteen, the carrier is divided into several categories? What is its characteristics?
A: It is usually divided into two major categories: diatomaceous earth and non-diatomaceous earth. Each category has various subcategories.
1. Diatomaceous earth type: (1) White: small surface area, loose, brittle, low adsorption performance, can be analyzed by strong treatment, and (2) red: large surface area and Good mechanical strength, but high adsorption.
2. Non-diatomite type:
(1) Fluorine carrier: It has good surface inertness and can be used to analyze high polarity and corrosive substances, but it is not easy to pack and the column efficiency is low.
(2) Glass microspheres: the surface area is small, and the column temperature can be greatly reduced by using the carrier, and the separation is complete and rapid. However, the coating is difficult and the column efficiency is low.
(3) Porous high polymer beads: high mechanical strength, good thermal stability, low adsorption, corrosion resistance, high separation efficiency, is a new type of chromatographic stationary phase with excellent performance.
(4) Carbon molecular sieve: neutral, large surface area, high strength, long sputum life, and incomparable superiority in microanalysis.
(5) Activated carbon: It can be used as a stationary phase alone.
(6) Sand: mainly used to separate metals.
14. What kinds of commonly used carriers are there? What kind of genus?
Answer: 101 carrier: white diatomaceous earth support; 102 carrier: white diatomaceous earth support; celite 545: white diatomaceous earth support; 201 support: red diatomaceous earth support; 6201 carrier: red diatomaceous earth support C-22 insulation brick: red diatomite support; chromosorb: red diatomite support.
15. Why should I use the carrier? What are the general treatment methods?
Answer: The surface of the commonly used support is not inert. It has different degrees of catalysis and adsorption (especially when the content of fixed solution is low and when the polar substance is separated), which causes peak tailing and column efficiency, and changes in retention value. Pretreatment is required. The general treatment method is briefly described as follows:
1. Pickling method: The carrier is heated and treated with concentrated hydrochloric acid for 20-30 minutes, then rinsed to neutral with tap water, rinsed with methanol, and dried for use. This method mainly removes inorganic impurities such as iron on the surface of the support.
2. Alkaline washing method: soak or reflux the carrier with 10% sodium hydroxide or 5% potassium hydroxide-methanol solution, then rinse with water to neutrality, rinse with methanol, and dry for use. The purpose of alkaline washing is to remove acidic sites such as aluminum oxide on the surface, but often a small amount of free alkali remains on the surface, which can decompose or adsorb some non-alkaline substances, and should be used when using.
3. Silanization: The silanization reagent reacts with the silanol or silanol groups on the surface of the support to remove the hydrogen bonding ability of the surface, and the performance of the support can be improved. Commonly used silylating agents are dimethyldichlorosilane and hexamethyldisilazane.
4. Glaze: The carrier to be treated is soaked in 2, 3% sodium carbonate-potassium carbonate (1:1) aqueous solution for one day. After drying, it is first calcined at 870 ° for 3, 5 hours, then heated to 980 °C. Calcined for about 40 minutes. After this treatment, a layer of vitrified enamel is formed on the surface of the support, so it is called "glazed support". The support has small adsorption performance and high strength. When a small amount of tailing agent is added to the fixing liquid, substances such as alcohol and acid can be analyzed. However, the efficiency of the non-polar material column is slightly reduced. In addition, methanol and formic acid have certain irreversible chemical adsorption on the glaze support, which should be noted in quantitative analysis.
5. Other purification methods: Any method that uses a chemical reaction to remove the active sites or physically cover to achieve the surface properties of the purified support can be used. 16. What is the number of commonly used carriers? A: Commonly used 4-6 mm inner diameter columns: for longer columns, the total number of substrates used is 40-80 mesh; for shorter columns, the total mesh size is 80-100 mesh (intra-inch) The number of sieve holes is for the purpose).
Seventeen, how to choose the commonly used carrier?
A: All kinds of bears have a wide range of names. In common diatomaceous earth supports: Red supports (such as 6201, 201) can be used for the separation of non-polar or weakly polar substances. A white carrier (such as 101) can be used for polar or alkaline substances. Glazed red supports (such as 301) can be used for moderately polar materials. The silylated white support can be used for the determination of highly polar hydrogen-bonded materials such as wastewater. Acidic substances, such as phenols, are separated by acid pickling. The alkaline substance, such as ethanolamine, is separated and the treated support is washed with an alkali. For silic analysis, a silanized support is used. In some special cases, special supports such as fluorine supports are used to separate isocyanates. However, in the ordinary constant analysis, it is not necessary to pay too much attention to the support, and even refractory brick powder, glass beads and sea sand can be used.
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