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    Home > Biochemistry News > Biotechnology News > Thin layers of analysis of the big problem to demystify.

    Thin layers of analysis of the big problem to demystify.

    • Last Update: 2020-10-29
    • Source: Internet
    • Author: User
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    -related topics thin layer analysis (TLC) technology 1. In thin layer analysis, the choice of expander is very important, I am engaged in synthesis time is not long, each time the selection of expander is not very appropriate, please teach you experienced teachersreply: a kind of The simple way is to choose one of the most polar solvents (e.g. alcohols, ethyl cyanide, etc.) based on the solubility of your production, and then slowly add the polarity of the weak solvent (e.g. carbon tetrachloride, petroleum ether, dichloromethane, etc.) to regulate the polarity of the system. for the best unfolding results.tell you my ancestral secret recipe PE (60-90) EtAc/PE=1:2 EtAc/PE/AcOH=15: 5:1 /AcOH/n-Butanol/H2O=2:1:1:1I have used these four systems for 8 years without any problems.I've been using ethyl acetate: cyclane, constantly adjusting the ratio until there is a satisfactory Rf value, there may be acid or alkali when dragging, I generally acetic acid and triethylamine. I've been using it for years, and it's all right. May wish to tryfrom the point of view of unfolding, really can do, if it is separation is not necessarily OK if the separation had to lower a little RF, or canamino acids
    have a special expander, commonly used butanol and water, and then add acid and alkalipolar small use of acetic acid Ethyl ester: petroleum ether system polarly large methanol: chloroform systempolar methanol: water: butanol: acetic acid systemtrailing can be added to a small amount of ammonia or ice acetic acid Can you stir methanol alone for half an hour without returning (20-30 degrees)? There is also I see in another book that ethanol is better, because methanol back to the silicone tape impurities also rushed down, I really do not know how to do well, please which master to help answer it. Thank you first!Reply: If you want something and want to separate things on the board is very open, you can take a part of the silicone with the product scraped down, soaked with acetylene (refer to the 2nd floor opinion), and then think about silicone, the solvent steamed dry on it!.3. With ethyl acetate, do you want to reflow ah? How long will it take? Will something on silicone not fall off if the temperature is low? Is there enough polarity with ethyl acetate? Can you completely swap things off silicone?: I usually use acetone. Do
    heat
    . Use a sealing tube instead of filtering the
    after
    .polarity of ethyl acetate is usually sufficient, not assured that more ethyl acetate can be added, but do not heat. Scraped silicone powder with ethyl acetate, stirring at room temperature for 2 hours, I have done hundreds of times never encountered problems. As long as the board can be separated, the resulting sample to do 400M nuclear magnetic basically do not see impurities.but I also have a lot of experience showing that methanol is no problem. Polarity is relatively large Dongdong (e.g. with pure ethyl acetate is not good to climb up), or need to use methanol, if the board is good, impurities will not have, but there may be a small amount of silicone tape under. I recommend the use of dichloromethane, easy to steam dry, and NMR is simple, but may be slightly less able to escape ethyl acetate, for the general
    compound
    is enough.. 4. Is chemie polar enough with dichloromethane? What's on silicone is hard to come down with, isn't it? And what is the lanthanum enchation tube, please? I never seem to use it! : You think, how polar are you generally the antisaling agent you use to climb a board or cross a column? Since you can rush down from the silicone column, why not wash it off the silicone? I haven't used it, I'd like to hear it. is a glass tube, the bottom of the retract, like a small column, no pistons. When using, plug in a small piece of skimmed cotton, pour the silicone powder scraped from the plate into it, wash it with acetone, and collect the dripping lotion from a round-bottomed flap below. Neither heating nor stirring is required.
    use pure acetone as an equantomy agent, for the usual polarity (chloroform: methanol: 4:1, silicone H, CMC, Rf>0.2) substances, can be completely purified. If the polarity is greater, try methanol. For dissolving reasons, try dichloromethane, such as triamcinolone. I've been using sandboards
    funnel
    , more worry-free, silicone powder will not wash down. core funnel is not washable, especially for insoluble substances such as silicone. Use alcohol or lotion immersion to remove
    organic
    , water recosting can remove most inorganic and insoluble, but there will always be some into the slit to remove unclean. It doesn't feel good. . 5. Excuse me, why not use the method of post-soak filtering? I have been using this method for convenience, but found that the impact on the yield is relatively large, is there any reason in it? answer: the problem of preparing thin layers is that the yield is much lower than the column layer analysis, dead adsorption is serious, because the column has been flushed with solvent. However, there is no way, but it is suitable for cases with low sample sizes. I have a lot of nuclear magnetism that is divided into plates. Methanol immersion is not recommended, there will be silicone peaks, hydrogen spectrum high field area is not good-looking. I am generally soaked with ethyl acetate or THF, shaking at room temperature for 1 to 2 hours, the hourglass funnel filter after spin dry can be. . 6. I want the amino acid methyl ester, now synthesized its hydrochloride, with saturated sodium bicarbonate solution to ph to weak alkaline, can not be extracted (with ether and ethyl acetate extraction, most of them are still in the water), please ask you how to solve? Reply: You do not use water, do not use sodium bicarbonate, but with organic solvents plus triethylamine to pH - 8-9 or so, seasonal ammonium salts precipitated, filtered out, the remaining your products in the solvent, but do not use ethyl acetate, methanol, acetone, tetrahydrofuran and other extremely large solvents, will dissolve the season ammonium salt, preferably using toluene, ethyl acetate, chloroform, dichloromethane and other medium-polar solvents. Thyethyethamine hydrochloride dissolves in dichloromethane, and I've done hydrochloroacetamine in dichloroethane, can't get ester in dichloromethane into ammonia, ammonium chloride in dichloromethane is basically insoluble Filtration, filter cake is ammonium chloride, filter steamed dry, is the amino acid esters you want. I used to make ethyl acrylates, from acid to esters, yield more than 80%. . 7. Anti-pillar method for substances that are too polar. With activated carbon, cheap, how effective? C18 equivalent high, regeneration effect? hope that the teacher who has worked in this area will guide his mind. I separated the sample after two points is not easy to come out, increase polarity when the tail mixed together out, intended to use polar column reply: C18 price is high, but as long as good use, do not use chloroform and other solvents wash, a column can be used many times repeatedly. The impurities with low amount of activated carbon removal point are OK, especially the decolorization effect is good. Your sample does not explain the nature, not good to give you advice c8, c18 pillars, with methanol: water, gradient wash, good results! If the acid or amine can be added a little acetic acid or triethylamine using a smaller than the point plate polarity of the expander slowly over. . 8. Recently need to use the preparation type of thin layer, but has not been contacted before, please ask the preparation type of thin layer of CMC adhesive solution concentration is the best ah? What kind of problems should be paid attention to when carrying out the preparation thin layer test??? Reply: I used to do thin layer preparation in the company, now in school, may remember not too clear: should be 2.5-5/1000, simply put, is 2.5-5 grams of CMC water to 1000ML and then slightly heated, or not heated, with electromagnetic stirring, as far as possible dissolved, can be used directly, preferably filtered, but filtering is slow, be patient! I remember we used to keep the pump filtering during the day, no matter what it was, and do something else! Also, when using 20X20CM glass plate for preparation, the silicone and CMC solution mixed (figuratively 1 g more than silicone, CMC solution 3ML), generally speaking, 20X20CM glass plate needs 20 grams of silicone and 60ML water, do not have bubbles, if any, can add a small amount of ethanol, and then stir, and then spread the plate evenly.
    in the air naturally cool dry, and then bake around 100 degrees to live, turn off the power, natural cooling, take out direct use on the line! I don't know if my memory is wrong, if so, petition volume! First wash the used plate with a general detergent, soak the plate in water, add a small amount of solid NaOH, cook on the stove for about an hour, then wash it with water,
    oven
    in 120 degrees coax 1 hour spare. 2) Make a solution of 0.6% methyl cellulose water, to be mixed evenly and then filtered. 3) Add silicone in the filtered methyl cellulose (note to have fluorescent oh chemical pure can be) and then spread on the coaxed board, although everyone will this method, but I found that the 0.6% ratio is a better to make CMC aqueous solution: called 3 g (or 5g) CMC-Na, put in a 1500mL conical bottle, add 1000mL distilled water, stir the magnets, heat the water bath 60-70 degrees, until clarified, set aside for a few days, let a small amount of flocs subside. Note that it cannot be filtered. (2) paved thin layer (PTLC) plate: 50-200mg samples can be separated. The 20 x 30cm glass plate is washed clean with washing powder on one side and dried face down to avoid dusting. The silicone HF254 (or HF254-365, or GF254) 15g (or 30g) is added to the above-mentioned CMC aqueous solution 45mL (or 90mL) in the study, and is fully ground evenly.
    a freehand paver or a paver, generally a thicker hand (30g silicone required) and a thinner paver (15g silicone). If you use a paver, you can lay several pieces at a time. The thin layer is laid dry overnight and can be used directly and, if necessary, 105 degrees before use for 1 to 2 hours. (3) A PTLC specifically designed to purify a small number of samples: 10 x 20cm, with 5g silicone, can be separated 5-20mg samples. pTLC is still a bit of a heart, and now it's helpful to give it to you. cmc-Na preparation: we must have had the experience of cmc in the water on the group, to cook hard to get done, even the method can be done once and for all - the cm with ethanol or acetone hanging, in the stirring slowly added to the water, slowly speed up the stir.
    so that cmc is more evenly dispersed in the water, just a little boiling can be clarified. :) plate is due to the board did not wash clean, it is best to rub with organic solvents in the shop, sometimes the board is too thick will also appear cracking plate, so 20 x 20 plate general silicone is not beneficial more than 30g / sheet. , what effect does floc precipitation have on the paving board? Does not sink whether it is possible. I think the key is to wash the board clean, I generally use ethanol-alkali lotion bubble for two days, must be very clean, it is very good to lay. I dissolve CMC with cold water stirred evenly, then heated, basically no flocs, concentration with 0.5% can be. . 9. Please demystify: Silicone
    the general
    of the column. For example, the choice of semen. Problems related to the upper column of the dry and wet methods??? : The polarity of the escape solution depends entirely on the TLC. Dry and wet upper column is essentially no different, pay attention to the column do not dry. In addition, the top sample should be uniform. It's a coincidence. mainly rely on doing more, familiar can make a coincidence. The semen is mainly by trying it. But you can also check the chromatography of the book. column must not crack, sometimes the change of solvent polarity will cause the column to crack. 8th floor brother, the column runs cracking because the polarity changes too much, to gradually change the polarity 10. Wet method and dry method which column effect is better? : I used to learn to plant, so say two sentences about column analysis. 1 dry column method is more suitable for lazy people, and if the composition is not complex, thin layer points are also separated good, fully able to meet the requirements. 2, wet column effect is good, provided that the column bed to balance well, generally with the flow phase to balance 3-5 retained volume.
    pressure effect is certainly better, the middle of the column is not easy to appear bubbles and other phenomena, and the speed is fast enough. 3, decompression column in addition to the speed, no advantages, but for special circumstances, such as the removal of a major component of some small amounts of impurities, but also very easy 4, about thin layer conditions h and column analysis conditions of the relationship.
    the general column analysis (200-300 eyes) of the filler silicone adsorption capacity is a little weaker than the thin layer filler (300-400 eyes). Therefore, in principle is to choose the asking ingredients on the thin layer RF to 0.1-0. Conditions between 3. 5, the selected solvent in addition to considering the polarity size, there are two factors,
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