You are watching: Are rf values unique to a compound
What is TLC?TLC stands for Thin Layer color layer analyzer the is one analytical technique that deserve to be used to monitor reactions and also for the qualitative evaluation of facility mixtures and for the identification of unknown compounds. that is likewise important for determining the correct solvent system with which to run a obelisk chromatography in. TLC is composed of two phases, a mobile and a hard phase. The solid phase is a thin solid support that usually is composed of Alumina or Silica. The mobile step is a solvent that moves through capillary activity right v the heavy phase. In general, the solid step is generally polar while the mobile solvent is non polar relative to the hard phase. Friend cannot recover your compound from the TLC plate so keep this in mind if you have small amounts the compound.
How to pick the solvent system?The choice of the solvent counts on the nature of compounds the you desire to separate and the nature that the solid assistance you room using (ie, is the silica or alumina). For example, if one impurity in a sample is nonpolar, the impurity deserve to be gotten rid of using a nonpolar solvent favor hexane if a polar Silica solid step is being used. Likewise, if the compound of attention is polar, climate it will have a strong affinity with the polar Silica heavy phase and thus, will not be eliminated in the non polar solvent. The compound deserve to be eluted utilizing a more polar solvent such together ethyl acetate or ethanol. Keep in psychic that also high a concentration of methanol can dissolve the silica (~10%).
Some common techniques for visualizing the outcomes of a TLC plate include (if girlfriend cannot check out it v your eyes): UV light ( mental to use the UV goggles) Iodine Staining: is an extremely useful in detecting carbohydrates because it transforms black on contact with Iodine KMnO4 stain (organic molecules) Ninhydrin Reagent: frequently used to detect amino acids and also proteins
Whenever handling the TLC plate try to usage gloves together your fingerprints can give some extra spots. If dealing with with your hands, organize the TLC plate follow me the edges.
How to translate the TLC?
The behaviour of a link on a TLC is usually explained in regards to its loved one mobility or Rf value. Rf or Retention element is a distinctive value because that each compound under the very same conditions. The Rf for a link is a constant from one experiment come the following only if the chromatography conditions listed below are likewise constant: solvent device adsorbent thickness that the adsorbent quantity of material spotted temperature due to the fact that these components are difficult to keep consistent from experiment come experiment, loved one Rf values are usually considered. “Relative Rf” way that the values room reported loved one to a standard, or it method that you compare the Rf worths of compounds operation on the very same plate in ~ the very same time.
The last results because that the TLC have to look favor a series of dots. If you can visualize the spots then the Rf value deserve to be calculated.
The Rf value is calculated making use of the adhering to equation:
based upon the Rf values, the identity and characteristics the the various compounds can be determined. An ext polar compound will have smaller Rf values because they will have a stronger affinity because that the polar solid phase. This would an outcome in the compound no being carried very far along the TLC plate. Compound with larger Rf values interact strongly through the less polar mobile phase and thus, often tend to it is in non polar themselves. Sometimes it is impossible to check out a great separation top top TLC. The snapshot looks smeared; this may be due to the enhancement of too much sample or evidence of the presence a most impurities. Also, if the side and bottom of the TLC plate is no flat, the solvent front may migrate unevenly.
Limitations of TLC
Although that is a very simple and convenient technique, one of its constraints is the it cannot tell the difference between enantiomers and some isomers. Another disadvantage that TLC is the in order to identify details compounds, the Rf values for the compound of interest should be well-known beforehand.
Steps and Procedure for to run a TLC
first obtain a TLC jar/chamber and include the TLC solvent to it. Add filter document that is the very same size together the TLC plate into the seasoned to assist equilibration. Nearby the TLC jar for 5-15minutes to allow for equilibration. Attain the sample to it is in spotted. You must dissolve this sample (even if the is liquid) in an appropriate solvent in order to spot that on a TLC. Use a sample vial, test tube, or small flask to dissolve her sample. Use a solvent with a short boiling suggest if possible (acetone or methylene chloride for example). This solvent could be quickly evaporated. Obtain a clean TLC plate from the box/desiccators. (Use gloves, oil indigenous hands have the right to contaminate the TLC). Mark a line (using pencil) that is greater than the solvent in the TLC jar and also mark down wherein the sample have to be spotted. Usage a capillary tube to spot the sample top top the TLC plate. You can spot it several times if the concentration of your sample is no high. Air dried TLC key after each spotting (use a blow drier to evaporate off greater boiling suggest solvents). Your sample spot have to not be broader when 4-5 mm in diameter. The smaller sized the diameter the the spot, the better resolution you will observe. Placed the TLC plate right into the TLC jar such that the begin line is parallel come the TLC solvent. Collection the TLC come a slim slant and then near the seasoned lid. Protect against the TLC when the solvent former is close to the peak by acquisition the TLC out of the TLC jar.
See more: If A Volcano’S Magma Is High In Silica, The Volcano Will Probably A
Mark down the ar of the solvent front for determining the Rf values.