CHM 111 Column Chromatography (CC) Lab PDF

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Summary

Taught by Professor Aliana Lungu...

Description

Column Chromatography (CC) ● Stationary phase ○ Polar solid adsorbent (Al2O3 or SiO2) ○ Packed into column ● Alumina activity type ○ Activity II (neutral form) for CC ○ Alumina as purchased will usually be activity I, meaning it will strongly adsorb solutes, and it must be deactivated by adding water, shaking, and allowing the mixture to reach equilibrium over an hour or so ○ Usually activity III on TLC plates ○ Brockmann activity

I

II

III

IV

V

% by weight of water

0

3

6

10

15

● Mobile phases/solvents ○ Polarity: hexane (nonpolar), mixture, MTBE (polar) ○ How to choose a solvent or solvent system: should be less polar than the compounds, compounds must be soluble in the solvent so they are not permanently adsorbed ● Calculating % recovery following a CC separation of mixture of known composition: mass recovered ∗100 % recovery = ○ initial mass ● How can TLC be used to assess the quality of separation by TLC? ○ If the separation of the pure mixture aligns with the separated spots of the sample, then the quality of separation was good ● Sample and column size: ○ Amount of alumina or silica gel used should weigh at least 30 times as much as the sample to be separated ○ Column should have a height at least 10 times the diameter ○ Density of silica gel is 0.4g/mL and density of alumina is 0.9g/mL 2 ○ Volume of a cylinder =π r h...