Summary: Analytical Methods In Organic Chemistry

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• 2 Sample Clean-Up

• 2.1 Paper on brightspace

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• Why don't  compounds that enter steam distillation and headspace technique need pre-treatment?

  Compounds that enter steam distillation and/or headspace don't need pre-treatment because steam distillation and/or headspace techniques are very selective; they remove most unwanted non-volatile substances, so the extract is already clean enough for direct GC injection

• Why is sample pre-treatment/sample purification sometimes needed before injecting into an HPLC, GC or CE apparatus?

  Sample pre-treatment/sample purification is sometimes needed before injecting into an HPLC, GC or CE apparatures because extracts obtained by solvent extraction often contain many different classes of compounds and some of these unwanted matrix components could interfere with subsequent HPLC, GC or CE analyses

• What is the principle behind solvent partitioning as a sample clean-up technique?

  The principe behind solvent partitioning also called liquid-liquid extraction=LLE is partitioning between an aqeous layer and an immisicble organic layer in a separatory funnel. The analytes and matrix components divide themselves over the two layers according to their partitioning constants (K)

• Why is pH a powerful tool in liquid-liquid extraction (LLE)?

  PH is a powerful tool in liquid-liquid extraction LLE because the polarity determines whether it prefers the aqueous or organic layer, and its polarity can be changed by adjusting the pH. Charged molecules are more polar and prefer the aqueous (water) layer, uncharged molecules are less polar and prefer the organic layer

• What are common organic solvent in LLE?

  Common organic solvent in LLE that are relatively non-polar are diethyl ether, hexane and dichloromethane (DCM)
  Common organic solvent in LLE that are more polar organic solvents are butanol, ethyl acetate

• What are common substances used in LLE?

  Common polar substances used in LLE are water, sugars, alcohols, amines and carboxylic acid (especially if they are depronatonated/charged). 
  Common non-polar substances are waxes, oils/fats, chlorophyll and hydrocarbons, and many non-ionised organic molecules. They usually prefer organic layer like ether 

• What does pKa of a substance (weaks acids) have to do with LLE?

  The pKa of substance means how easily it can give away it's proton. When the pH is higher than the pKa it gives away it's, the environment is relatively basic and the molecule can give away it's acidic proton more easily. Then molecules becomes charged, more polar, more  solving in water

• What does pKa of a substance of a weak base (B) have to do with LLE?

  The pKa of a weak base means how easily BH+ gives up its proton. When the pH is lower than the pKa, a proton is added. THe base becomes charged, so more polar and prefer the aqueous layer

• What does K, the partition coefficient, stand for and how can it be interpreted?

  K, the partition coefficient (K) describes how a substance distributes between two immiscible solvents. 
  
  When K >1 the analyte prefers the organic later
  When K < 1 the analyte prefers the aqueous layer

• 3 Chromatography

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• Which technique is capable of the separation of closely related analytes?

  The technique is capable of the separation of closely related analytes is chromatography