Exercise 1 results


The video is posted at https://tube.switch.ch/channels/62aad1c4

First of all I would like to apologize for my horrible swiss coloured english. When I processed the video I had to listen to myself and it was much worse than I thought. There is no excuse, but some reasons – first of all I hated my english teacher and was lazy in grammar school, second, I spent my postdoc time in Norway and not in the US or UK as all the others. I hope on your generosity-

The overall performance was 67% of possible points, with no catastrophic failures. That’s a bit more than sufficient but in view of your very diverse backgrounds I am fine with it.

(*) point was granted also if only reasoning for difficulty was provided

Exercise 1 – the 100% answers

QuestionYour answer
Which property of a compound is relevant to make it suited for detection in HPLC/UV?Aromatic systems, the larger, the better
Which property of a compound is relevant to make it suited for detection by LC/MS?Ionizability = acidity or Brønstedt basicity
Which property of a compound makes it amenable for gas chromatography?Volatility
Which property of a compound makes it suited for liquid-liquid extraction?Hydrophobicity
You want to extract a weak acid with pKa 4.8 into an organic solvent. At what pH will you do this?pH < 2.8
Reversed phase HPLC; you examine the decomposition of Aspirine to salicylic acid. Which of the compounds is expected to elute first?Salicylic acid (more polar and smaller = elutes first)
Reversed phase HPLC with acetonitrile/acetate buffer, your peaks elute too late.How do you speed up the elution?Start at higher organic or/and steeper gradient
Thin layer chromatography (Adsorption/Silica with Toluene/Isopropanol). Your compound elutes too slowly, how can you reduce retention?Enhance Isopropanol percentage
Can we extract ascorbic acid from water? Any idea how?Very difficult – Maybe SPE with ion exchange cartridge *
How could we extract salicylic acid from plasma?Easy, Liquid-liquid, SPE, SLE at acidic pH
  • point was given also if a reasoning for the difficulty was given

Difficult questions

First of all, please read the questions carefully. Some of you made comments related to HPLC in the first questions, but the questions were uniquely referring to detection.

Some of you proposed equilibrium dialysis and column switching extraction methods for aspirine from plasma. Please think before you type, this was obviously Google. This answer could be taken from question 5..

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