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    Home > Biochemistry News > Biotechnology News > Book layer analysis

    Book layer analysis

    • Last Update: 2020-11-23
    • Source: Internet
    • Author: User
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    thin layer analysis is a simple, fast and trace layer analysis method. Generally the column layering adsorbents scattered to the plane such as glass sheets, forming a thin layer for layering, known as thin layer analysis. The principle is basically similar to column analysis. 1. The characteristics of thin layer analysis: the characteristics of thin layer analysis in application and operation and the comparison of column layer analysis.
    2. Selection of adsorbents: The adsorbents used for thin layer analysis are the same as their selection principles and column analysis. The main difference is that thin layer analysis requires a finer granularity of adsorbents (supporters), generally less than 250 eyes, and requires uniform granularity. Adsorbents or prefabribriated thin layers for thin layer analysis should not be too active in general, and should be graded II.-III. The spread distance depends on the particle size of the thin layer, the finer the particle size of the thin layer, the corresponding reduction of the spread distance, generally not more than 10 cm, otherwise it can cause
    chromatography
    diffusion affects the separation effect.
    3. Selection of expanders: thin layer analysis, when the adsorbent activity is a certain value (e.g. II.or III.grade), whether the sample of multiple parts can obtain satisfactory separation, depending on the choice of the expander. In the fat-soluble composition, the chemical composition of Chinese herbal medicine can be divided into non-polarity, weak polarity, neutral polarity and strong polarity according to its polarity. However, in practice, it is often necessary to adjust the polarity of the expander by using the polarity size of the solvent.
    4. Special thin layer: for the separation and detection of
    compounds
    of a particular nature, sometimes some special thin layer is required.(1) Fluorescent thin layer: Some compounds themselves are colorless, do not appear fluorescent under ultraviolet lamps, and there is no appropriate color agent, fluorescent substances can be added to the adsorbent to make fluorescent thin layer for layering. After the spread layer is exposed to ultraviolet light, the thin sheet itself shows fluorescence, and the sample speck does not show fluorescence, you can detect the photorefective position of the sample. Most commonly used fluorescent substances are inorderable. One is to
    254nm of ultraviolet light, such as manganese-excited zinc silicate. The other is fluorescent at 365nm UV light, such as silver-excited zinc sulfide.(2) Lyme thin layer: commonly used with silver nitrate thin layer, used to separate the number of carbon atoms equal and
    C one C double bond number of a series of compounds, such as unsaturated alcohols, acids and so on. Its main mechanism is that the C-C bond can form a bond with silver nitrate, while the saturated C-C bond does not bond with silver nitrate. Therefore, on the thin layer of silver nitrate, the chemical table can be separated due to the different saturation degrees. Saturated compounds at stratography are the highest rf due to the weakest adsorption, with a higher RF value of two double bonds with one double bond and a higher rf value with one double bond. In addition, in a dual-bonded table, the smooth and silver nitrate combination is easier to carry out. Therefore, it can also be used to separate the transverse isomer.(3)
    acid-base
    thin layer and
    PH buffer thin layer: in order to change the original acid-alkalinity of the adsorbent, thin acid or thin alkali can be used in the laying of thin layer instead of water modulation thin layer. For example, silicone tape slightly acidic, sometimes the separation of alkaline substances such as alkaloids is not good, if you can not spread the layer or tail, you can lay thin layer, with a dilute alkali solution 0.1 to 0. 5NNa0H solution is made into a thin layer of alkaline silicone. For example, when silicone is used as an adsorbent, chloroform-acetone methanol (8:2:1) is used as the < 0. 1, the use of alkaline silicone thin layer with the same expander, rf value increased to 0. 4 or so. Explain that pig poo bean base is -- alkaline alkaloid.
    5. Application: Thin layer analysis method is mainly used in the study of the chemical composition of Chinese herbal medicine, the pre-test of chemical composition, the identification of chemical composition and the exploration of the conditions of column separation.test of Chinese herbal chemical composition by thin layer analysis method, which can be carried out according to the properties of various ingredients and well-known conditions. Since some impurities can be separated after spreading over the thin layer, the selectivity is high, which can make the pre-test results more reliable.the chemical composition of Chinese herbal medicine by thin layer analysis method, it is best to have standard samples for co-thin layer analysis. If the
    Rf values and speckle shape colors of
    Sysm standardsand identifications are identical after the spread of several solvents, the preliminary conclusion can be drawn that the same compound. However, chemical reactions or infrared spectroscopy
    are
    to be checked by an instrument analysis method.to explore the separation conditions of the column layer by thin layer analysis is the conventional method of the laboratory. In the separation of the column layer, the first consideration is to choose which adsorbent and enchantment agent. In the process of wastation of the individual ingredients will be in what order, each was a single ingredient or mixture, can be determined and tested by the separation of thin layers. Through the pre-separation of thin layers, you can also understand the composition and relative content of multi-component samples. If a more satisfactory separation condition is found on a thin layer, this condition can be used for dry column analysis. However, the thin layer separation conditions can also be appropriately changed, to the general method of escape to the layer to prepare column separation. When using the pre-separation of the thin layer to find the escape condition of the column layer
    , it is assumed that the RF value measured on the thin layer is the ratio of a sample in the column layer (R). This is due to the continuous evaporation of the solvent contained in the fixed phase of the thin layer as the thin layer unfolds, so that the amount of solvent contained at various points on the thin layer is unequal, and the content near the starting line is higher than the front part of the thin layer. However, if the conditions of the analysis operation are strictly controlled, close to the true Rf value can be obtained. The separation of a certain group is carried out by a thin layer, and its RF value range is 0. 85>Rf>0. 05。 In addition, thin layer analysis method is also applied to the inspection of the authenticity of herbal medicines, herbs and their preparations,
    scalue control
    and resource investigation, the process of controlling chemical reactions, the inspection of reaction by-products, intermediate analysis, chemical and preparation impurities inspection, clinical and
    biochemical
    testing and toxic analysis, etc., are effective means.
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