Abnormal causes such as tailing in thin layer chromatography experiments and methods to overcome them

-related topics thin layer analysis (TLC) technologythin layer
chromatography
method is a commonly used micro-analysis method, widely used in herbal medicine research and daily testing, but often speckle anomalies bring difficulties to the results of judgment, should pay attention to avoid and overcome.1, tailing phenomenon trailing phenomenon is more common in thin-layer chromatography, resulting in blurred boundaries between spots, the result is difficult to judge.Cause and overcome method (1) dot excessive in the thin layer chromatography process
compounds
in the thin layer plate adsorption——— desorption process, any kind of adsorbent, their ability to load compounds is limited, due to excessive point and overload, the excess compounds are left behind, forming a drag phenomenon.(2) Repeated sample points although in the same vertical line and sample dot center does not re-consum, resulting in the sample point is near the elliptical shape, but also the formation of tailing phenomenon is another reason, in order to avoid the above anomalies, should choose a suitable sample amount and complex sample process, the sample dot center should be re-aligned.2, edge effect edge shovel should be the sample in the analysis, the specks on both sides of the thin sheet move faster than the middle spots, and skew to both sides. The reason is that in the process of expanding with mixed solvent, the solvent with weak polarity and lower boiling point is more volatile on both sides of the thin sheet, which makes the proportion of the expander on the thin sheet inconsistent, the polarity changes, and the edge effect occurs.In order to avoid the above phenomenon: increase the concentration of solvent vapor in the laminate cylinder, attach the
filtration paper
of the wet expander to the inner wall of the laminate cylinder, or select the inner diameter and length appropriate for the analysis of the analyzer. Choose a suitable single solvent instead of a mixed solvent. Co-boiling solvents are used instead of general mixed solvents.3, S-shaped and wave-shaped spotsS-shaped spots refer to sample layering with a variety of components, the spots are not distributed in the vertical line from the origin to the unfolding edge, but are s-shaped on both sides of the vertical line. Wave specks are sample fluids containing a variety of components, which are followed by the same starting line, and when expanded, the same spots with these components are not linearly parallel to the starting line, but are wavy.is caused by a thin sheet thickness uneven. In order to avoid the appearance of the above phenomenon should be selected thick and uniform thin sheet.4, candy spots candy spots refers to the small distance between compound spots, interconnected with beads.the cause and the method of overcoming: the sample has too many ingredients, in a certain length of thin sheet, the row does not open, overlap with each other. The length of the laminate can be increased appropriately, so that the speckle distance is increased or bidirectional analysis is used, so that the contents of the two directions can be expanded to avoid the appearance of bead-like spots. Multiple samples, the center of the dot does not fit, forming a complex spot. The sample should be given at an appropriate concentration once for the test fluid, and if it is sampled several times, the sample center must be re-combined.5, after unringing the speckled RF value unstable speckle RF value does not conform to the literature regulations or repeated operation of the RF value when large and small.main reasons are: the layering temperature is unstable, in the use of mixed solvents, due to temperature instability caused by the proportion of the expander changes. The thin layer is thick and uneven. Differences in the solvent quality of adsorbents. According to the above reasons in the process of layering in addition to the selection of better quality adsorbents and solvents, the same batch or the same variety should choose the same plant, the same batch number of adsorbents and solvents, the room temperature difference at the time of analysis is controlled between 5 degrees C, when making the plate adsorbent particles should choose diameter particle plate, plate flat, thin thin uniform.
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