Thin layer chromatography speckle tailing reasons - Database & Sql Blog Articles

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1. Causes and methods of overcoming

(1) Excessive Dosing In the process of thin-layer chromatography, compounds are adsorbed on thin-layer plates. During the movement of desorption, any type of adsorbent, their ability to support compounds has a certain limit. After the sample is overloaded and overloaded, the excess compound is thrown behind and forms a tailing phenomenon.

(2) Although the sample points of the repeated points are on the same vertical line and the center of the sample points are not coincident, the sample points are nearly elliptical, which is another cause of the tailing phenomenon. In order to avoid the above abnormal phenomena, the appropriate spot should be selected. During the volume and complex spotting process, the center of the sample points should coincide.

2,

Edge effect

The edge shovel should be such that when the sample is being chromatographed, the spots on both sides of the thin plate move faster than the middle spot and are skewed to both sides. The reason is that during the development process of the mixed solvent, the solvent with weaker polarity and lower boiling point is more volatile at both edges of the thin layer plate, so that the proportion of the developing agent on the thin layer plate is inconsistent, and the polarity changes, and appears. Edge effect.

In order to avoid the above phenomenon: increase the solvent vapor concentration in the ladle cylinder, paste the filter paper with the wet developing agent on the inner wall of the chromatography cylinder or select the chromatographic cylinder with the inner diameter and length to perform chromatography. A suitable single solvent is selected in place of the mixed solvent. An azeotropic solvent is used instead of the general mixed solvent.

3, S shape and waveform spots

S-shaped spots refer to samples containing multiple components. When the samples are chromatographed, the spots are not sequentially distributed on the vertical line from the origin to the front of the unfolding, but are distributed in the shape of s on both sides of the vertical line. Waveform spots refer to certain sample liquids containing multiple components, which are sequentially clicked on the same starting line. After unfolding, the same spots of these components are not linearly parallel to the starting line, but are wavy.

The reason for this is that the thickness of the thin plate is uneven. In order to avoid the above phenomenon, a thin and uniform thin plate should be used.

4,

Rosary

spot

Rosary

Spot refers to the small distance between compound spots and is interconnected.

Rosary

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Causes and methods of overcoming: There are too many components in the sample, which are arranged on a thin layer of a certain length and overlap each other. The length of the chromatographic plate can be appropriately increased to increase the spot distance or two-dimensional chromatography, so that the components can be spread in two directions to avoid the appearance of beaded spots. When spotting multiple times, the center of the spotting does not coincide, forming a complex spot. The test solution should be sampled at an appropriate concentration. If the sample is sampled multiple times, the center of the sample must be overlapped.

5. After the unfolding, the RF value of the spot RF value is inconsistent with the literature or when the RF value is repeatedly operated.

The main reason is that the chromatographic temperature is unstable, and when the mixed solvent is used, the ratio of the developing agent changes due to temperature instability. The thickness of the thin layer is uneven. Adsorbent solvent quality difference. According to the above reasons, in addition to selecting the better quality adsorbent and solvent in the chromatographic process, the same batch or the same variety should choose the same plant, the same batch of adsorbent and solvent, the room temperature difference is controlled between 5 °C during chromatography. When making the plate, the sorbent particles should be selected from the diameter of the plate, the plate is flat, and the thickness of the thin layer is uniform.