Acids, bases, and strongly polar compounds often produce streaks rather than spots in neutral solvents. Adding a few percent of acetic or formic acid to the solvent can correct streaking with acids. Similarly for bases, adding a few percent triethylamine can improve results. For polar compounds adding a few percent methanol can also improve results.
The volatility of solvents should also be considered when chemical stains are to be used. Any solvent left on the plate may react with the stain and conceal spots. Many solvents can be removed by allowing them to sit on the bench for a few minutes, but very nonvolatile solvents may require time in a vacuum chamber.
Volatile solvents should only be used once. If the mobile phase is used repeatedly, results will not be consistent or reproducible. Developing a TLC plate requires a developing chamber or vessel. This can be as simple as a wide-mouth jar, but more specialized pieces of glassware to accommodate large plates are available. The chamber should contain enough solvent to just cover the bottom. It should also contain a piece of filter paper, or other absorbent material to saturate the atmosphere with solvent vapors.
Finally, it should have a lid or other covering to minimize evaporation. If fluorescent plates are used, a number of compounds can be seen by illuminating the plate with short-wave UV.
Quenching causes dark spots on the surface of the plate. These dark patches should be circled with a pencil. For compounds which are not UV active, a number of chemical stains can be used. These can be very general, or they can be specific for a particular molecule or functional group. Iodine is among the most common stains. Plates are placed in a jar containing iodine crystals, or covered in silica gel with iodine dispersed throughout, for approximately one minute.
Most organic compounds will be temporarily stained brown. Some popular general use stains are Permanganate, ceric ammonium molybdate CAM , and p-anisaldehyde. These can be kept in jars which plates are dipped into, or in spray bottles. To develop a plate with permanganate, spray or dip the plate and heat it with a heat-gun. Hold the plate face up 10 to 20 cm above the heat gun until the bulk water evaporates. Overheating will turn the entire plate brown, obscuring the spots.
If glass plates are used it is often easier to see spots through the backing because it is harder to overheat. CAM and p-anisaldehyde stained plates are developed similarly. Overheating CAM stained plates turns everything blue. There are common problems in TLC that should be avoided. Normally, these problems can be solved or avoided if taught proper techniques.
Rarely, water is used as a solvent because it produces an uneven curve front which is mainly accounted for by its surface tension. Thin layer chromatography of three analgesics and caffeine under U. It is not a recommended technique in the laboratory. Due to the nature of the uv hazard polycarbonate safety spectacles which absorb short wavelength U. The samples were dissolved in ethanol for spotting onto the plate.
The TLC plate was run in an open beaker under short wavelength u. The movement of the dark purple spots samples during the running of the plate can be observed in the animation. Also it has a wide application in identifying impurities in a compound. It can be used as a preliminary analytical method prior to HPLC.
The concept of TLC is simple and samples usually require only minimal pretreatment. This decision is based on the Table 8. When assessing the type of stabilizer, take into account the precise identification of the stabilizer, whether it is centralit ethyl centralit, EC or C1 or diphenylamine DFA or DPA.
The purple color indicates the presence of centralite and diphenylamine DPA is considered or estimated as a more active stabilizer showed in Table 9.
The experiment is performed on a small quantity of gunpowder or it extract in dichloroethane. Two drops of the appropriate reagent are added to the gunpowder sample, whereupon the color appears according to the table above.
To determine the content of the stabilizer by the thin layer chromatography method, the sample is a gunpowder extract. In the experiment we extracted gunpowder samples in dichloroethane. The gunpowder can be mono-basic, double-basic or multi-basic. If as a result we get is intense purple dyeing, then it's a double-basic gunpowder. Nitroglycerin or some other nitrate ester, as the second energy base in the powder - mild violet color is not a proof of nitroglycerin.
Double-base rocket propellants are nitrocellulose NC -based energetic materials with a tendency towards slow, but constant thermal decomposition during aging.
The development of samples on the TLC panel is shown in the Sample application paragraph. First, add the appropriate solution in a glass chamber to cover the bottom in a thickness of 2mm of liquid.
The solution we pour into a glass bottle is selected as follows:. After drying, in a darkened room, and under UV light, mark the visible points or points with their own color like in Figure 5. Estimation of gunpowders with stabilizer diphenylamine is based on the information shown in the Table 4.
It is essential to compare the TLC plate of the sample with the standard in the Figure 5 Figure 6 according to. Centralit is clearly recognizable, nitroso-ethylaniline and 4-nitro-centralite are clearly recognizable.
Nitrozo ethylaniline and 4-nitro-centralite are clearly recognizable, dintro-centralite is eventually recognizable, centralit is still recognizable. Dintro-centralite recognizable, nitrozo-ethylaniline and 4-nitro-centralite recognizable, the centrality virtually disappeared.
Each country has its own categorization, and the indicative categorization is given in NATO standards. Smaller caliber ammunition contains 0. The results of the described experiment, in the titles above, are shown in the following Table The same gunpowder samples were examined on TLC and two additional methods and we will make a comparison of the results. We analyzed 11 different samples of gunpowders of 6 types of cartridges 20mm, 40mm, 76mm, mm, mm, mm.
The results were processed and passed the appropriate categories and in the table above we can compare the categories obtained by the TLC method with the categories adopted on the basis of the other two methods: HPTLC and VST. The main stabilizer according to TLC is determined chemically where the result of the reaction is dyeing, as explained in the title Determine the type of stabilizer.
Eight samples showed a category matching, these are samples no. The classical method depends on the eye of the observer, and this can be the cause of the different results.
Sample number 4 showed a stabilizer ratio of 1. We conclude that this is a transition group, as shown in Table 5 Table 12 by mixed green-yellow color. Sample number 5 is similar, however, the content of DPA is very high and the cause of disagreement in this case is probably human eye or inexperience. With this sample of gunpowder we can not say with certainty that it is the first category for HPTLC because we do not know how much the initial concentration of DPA was in the gunpowder.
In this case, we were guided by a theoretical mean concentration of DPA quoted in gunpowders, about 1. Samples 4, 5, and 7 belong to the transition group according to the TLC qualitative method, and because the method is qualitative, the attitude of our laboratory is to take a tougher decision, and this is one reason for disagreement with the mathematical decision of the other two methods.
Obviously, this is a good matching result, and also, for this sample the initial concentration of the DPA stabilizer is not known. Samples 8, 9, 10 and 11 clearly showed the third category, which was confirmed by the other two methods. Clarity in determining the third category is the most important in this experiment. In this case, it is confusing which grade to select from Table 4 Table Analyzing Figure 6, we can conclude that this is the sample in life range between E and F.
In practice, there is a high likelihood of errors in these cases. In such confusions, we advise group work, or to make a quantitative experiment on one of the appropriate methods. The method of interpreting the results leads to apparent disagreement of the categories for the three samples under the numbers 4,5 and 7 in Table For these three samples, this means that they are closer to the 2nd than the 1st category.
Obviously, the results of the TLC method are very useful and usable for the purpose of life prediction of ammunition. Thin layer chromatography for the purpose of qualitative analysis of gunpowder samples is a reliable method and largely depends on the expertise of individuals and from the interpretations of the results.
Results of qualitative thin layer chromatography analysis provides very good guidance in purpose of life prediction of gunpowders. Thin layer chromatography method can be economically employed for routine use because the consumption of mobile phase is low and, hence, there are scarcely any disposal problems.
Thin layer chromatography method does not require the use of machines or special devices, it is fully portable and easy to handle and considerably cheaper than most commercial methods. This is an open access article distributed under the terms of the, which permits unrestricted use, distribution, and build upon your work non-commercially. Withdrawal Guidlines. Publication Ethics. Withdrawal Policies Publication Ethics.
Home IJBSBE Application of thin layer chromatography for qualitative analysis of gunpowder in purpose of life prediction of ammunition. International Journal of. Research Article Volume 5 Issue 1. Figure 2 TLC plate with developed samples. Figure 4 Developing chambers and saturation. A Diphenylamine spot is much stronger than nitrodiphenylamine; barely recognizable 4-nitro-diphenylamine and 2-nitro-diphenylamine.
B Diphenylamine spot and nitrodiphenylamine are clearly dispersed, 4-nitr-diphenylamine and 2-nitro-diphenylamine clearly recognizable. C Diphenylamine spot is less intense than nitrodiphenylamine, 4-nitro-diphenylamine and 2-nitro-diphenylamine clearly recognizable. D Diphenylamine spot has virtually disappeared; Nitrodiphenylamine clearly recognizable, 4-nitro-diphenylamine and 2 nitro-diphenylamine are clearly recognizable, no dinitroproducts are not recognizable.
E Nitrodifenylamine recognizable, dinitroproducts are recognizable. F Nitrodifenylamines are not recognizable, dinitroproducts are recognizable. Table 4 Definitions of DPA stabilizer image. Given these uses, TLC does prove to be a nifty analytical technique in the field of biology.
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