Chromatography

Discussion in 'Supporting Chemistry' started by Jimbob1988, Sep 5, 2019.

  1. Morning all,

    Hope everyone has enjoyed their break(?).

    Setting up a chromatography practical using colouring pens. I am using the chromatography paper, and have checked that I have cut it evenly and not allowed it to touch the side of the beaker, in addition to keeping the water line below the pencil line.

    I am finding that the water is rising up the paper unevenly which is making it hard to allow students to do their calculations of substance movement/solvent movements.

    Any ideas why this might be?

    Many thanks!
     
  2. The answer is that the paper has been compressed. Also you will get better results if the Mobile Phase (deionised water) contains 0.1% w/v Sodium Chloride. Good luck and let's know how it goes.:);)
     
    Tanya D likes this.
  3. Best done with Chinese Lantern paper.
    pen.png
     
  4. Thanks for your advice.

    I will try the salt method as I won't be able to get hold of the other paper in time.

    Once again, thank you.
     
  5. You can use ordinary Chromatography paper provided you ensure that the samples are spotted with a good spacing.:)
     
  6. I drew a set of "fake" results in Word. That way the students can have a go and see how it works but have something to stick in their books and calculate the rf from. I've changed schools so I don't think I still have them, otherwise I'd offer to email the sheet.
     
    GeorgetheScienceTech likes this.
  7. Now that is what I call a Tech Cheat Alice, but is definetely useful in the event that students fail to get any results.:D
     
    Shannon and Alice like this.
  8. I know that the Chromatography of Inks in pens is performed by almost eveyone but the zones given by the various coloured pens are rather broad when the seperation is performed on chromatography paper and on TLC plates (nirocellulose backed) which makes determining Rf values difficult and inconsistant. I prefer to seperate Plant Pigments on TLC plates as the method is extremely robust and the bands formed are very narrow and precise allowing Rf values to be determined very accurately. I've just trialled the practical for AS and A2 which will take place tomorrow and Friday. I suppose you could edit it with a Pho Editor to show th colour and relative position of the bands.:);)
    pp3.png
     
  9. I used food colourings. Sugarflair spectral do a few which are single-spot. Fuchsia, Melon, Ice blue and Chestnut work.
     
  10. We do this on a micro scale with our GCSE students and it works very well. We also provide a UV torch to help make some of the less easily seen bands more visible.
     
  11. I'm surprised that a UV source works well as none of the pigment should fluoresce as they don't have an aromatic ring.:)
     
  12. The coating glows, many of the bands don't, kind of a negative staining effect.
     
    GeorgetheScienceTech likes this.
  13. Now I know what you meant Helen. Yes that would work provided the TLC plates contain the 254 nm uv indicator.:)
     
  14. karen b

    karen b COMMITTEE

    We follow the Cleapss new version using various indicators
     
  15. What's the new version Karen?:)
     
  16. karen b

    karen b COMMITTEE

    It is document PP049. It uses sodium hydroxide as the solvent, with four seperate indicators and a mix of all four.
     
  17. Another TLC of Plant Pigments Jimbob.:)
    imageedit__3098568912.png
     
  18. Here's my file...
     

    Attached Files:

    GeorgetheScienceTech and Tanya D like this.
  19. Absolutely fab Alice. Many of the Members of this Forum should get a copy while theycan. You truely are a Grand Master of Tech Cheats!:D:D:D
     
  20. Thanks George. :oops: