super quiz 2.pdf - TLC Precautions to take when preparing...

Info icon This preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
TLC Precautions to take when preparing for spotting, developing and visualizing and why undesirable results are observed if precautions not adhered to – impact on observations and results and measurements if precautions not followed, actions that would cause and reasons for these flawed observations/results. (know what plates would look like) Spotting - use capillary tubes, try to make spots small and compact by lightly touch TLC plate being careful not to flake off any adsorbant, the sample should not be too concentrated, overspotting leads to poor separation and smeary spots Developing - -make sure the solvent is below the spotting line so that the solvent does not dissolve samples on the spotting line -make sure top is placed back on so solvent does not evaporate, evaporation of solvent during this stage causes the development of the TLC plates to be messy and ineffective -make sure solvent does not rise up past the solvent front 5mm line, if it does, spots in the visualization stage will be difficult to evaluate (Rf values would be too high) -make sure the filter paper is in the developing chamber to saturate the developing chamber with solvent vapors -use tweezers to place the plate in the chamber, finger oils can smear or ruin the TLC Visualizing - Use UV light for conjugated compounds Use iodine vapor for most other compounds Why pencil needed to mark and why ink is never used graphite is inert and will not chromatograph, ink is organic and will chromatograph How polar eluents aid in moving polar compounds on TLC plate the more polar eluent the more rapidly it will move up Capillary action definition and how and when it happens in the TLC experiment at different stages it is the ability for liquid to fill in between solid particles in opposition to gradational force. occurs when spotting in tlc plate when solvent flows into spotting capillary via cap action and during plate developing step when solvent travels up TLC plate via capillary action Sample preparation specifics and characteristics of solvents used for preparation and why (impact on spotting as well) characteristics of solvents is volatile, mixture must be soluble in solvent, low viscosity and low boiling point to migrate rapidly, polar solvent carry polar substance up TLC plate (too polar high RF value) and non polar substances carry non polar substances up TLC plate (too non polar stay at bottom and low RF). silica used for very non polar compounds, alumina for very polar compounds
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
What are typical characteristics for solvents used as eluents (besides polarity and substance solubility) and why important characteristics for solvents as eluents volatile, solubility, and low viscosity Characteristics of solvents (polarity, solubility, volatility etc) used with respect to samples Characteristics of solvents that allow them to migrate rapidly
Image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern