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Summary Analytical Methods in Organic Chemistry
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Extraction and Chromatography
Sample extraction and pre-treatment
Percolation (coffee machine)
Liquid slowly passes through a filter
+ entire extraction with fresh solvent
+ no filtration afterwards
- much solvent is needed (& needs to be evaporated)
- stirring is difficult
Maceration (tea)
Soaking (raw agricultural) ingredients in liquid so it softens, draws out natural juices
+ simple
+ little solvent
- poor extraction when using analytes with low solubility
- filtration needed
Soxhlet extraction (continuous percolation)
Automated eternal percolation, liquid extraction utilizing solvents at low pressure and boiling
temperature
+ automated
+ good extraction yield
+ low solvent consumption
- electricity and cooling water needed
- thermal decomposition/thermolyse
Steam distillation
Suitable for nonpolar volatiles with bp 120-325 graden
Volatile compounds have high vapor pressure and low water solubility
Hot steam removes non-polar volatiles
+ very selective
+ Simple and cheap
+ Compounds with high bp can be isolated below 100 degrees
+ All volatiles isolated as 1 group
- thermal decomposition/thermolyse
- No separation between volatile compounds
- Compounds must be (water)insoluble
Static headspace
Extraction of volatiles, after equilibrium headspace is injected
+ selective
+ no solvent
- calibration solution is difficult to prepare
, SPME (Solid Phase Micro-Extraction)
Extraction of volatiles, coated fiber is used to concentrate compounds from sample
+ senstive
+ Solvent-free
LLE (Liquid-Liquid Extraction)
To purrify dissolved extracts
Polar compounds to aqueous phase
Non-polar compounds to organic phase
+ relatively cheap
SPE (Solid Phase Extraction)
Modern version of LLE, for treatment of small amounts of extracts
+ small amount solvent(s)
+ No emulsions
Chromatography
Separation of closely related analytes
Analytes are transported out of the column by mobile phase
Partition coefficient: K D=concentration∈ stationary phase /concentration∈mobile phase
High Kd means preferation of staying in stationary phase (and elute slow)
Phase ratio: β=volume mobile phase /volume stationary phase
Capacity factor: k ' =mass stationary phase /mass mobile phase= K D /β
k ' =k i =t ' r /t m
Resolution: R s=(t r 2−t r 1 )/(0.85 (w1 /2 1 +w 1/ 22 ))
- 1 = poor separation
- 1.5 = modest separation
- 2 = good seperation
Selectivity factor: α =k ' 2 /k ' 1
→ increasable; changing solvent or stationary phase
Band broadening (van Deemter equation)
H= A +B /u+(concentrationmobile phase +concentration stationary phase)u
→ H= A +B /u+ Cu
u = linear velocity of mobile phase
A-term: path length variation and average speed variation cause band broadening
B-term: axial diffusion (along axis of column) caused by differences in concentration
- decreases when u is high
C-term: non-equilibrium diffusion, caused by time needed for diffusion, adsorption and
desorption
- decreases when u is low
Quantitative Analysis
Always: 1 calibration solution and 1 sample solution
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