Transcript Introduction to analytical separations: SPE and SPME

Parts of slideshow courtesy of Adam Hall, Instructor of Forensic Sciences,
Boston University

Separation of analytes from a liquid matrix by the use of
another liquid (solvent) based upon selective
partitioning

aka. Solvent Extraction

Suitable solvents are selected based on their abilities to
partition target analytes within a liquid matrix

Consider:
 Miscibility of solvents: EtOH and Water vs. Pentane
 Immiscible solvents are employed for liquid-liquid extractions

Remember: like-dissolves-like

Consider:
 Ionic, non-ionic, polar, and non-polar analytes
 Acid / Base / Amphoteric Nature of Analytes
 Solubility of Salts … i.e. Cocaine Hydrochloride (HCl)

General Comments:
 Neutral molecules are soluble in organic solvents
 Charged species are water soluble

Manipulation and control of pH maximizes separation
efficiency with LLE’s and SPE’s

Ionization of a compound alters its physical behavior and
properties such as solubility and lipophilicity
▪ Ionization will increase a compounds solubility in water
▪ However, ionization will decrease a compounds lipophilicity

Ionizable groups:
carboxylic acid
O
 Carboxylic Acids
R
OH
pKa approx. 5
carboxylate
will deprotonate
with NaOH
and moderately
strong bases
phenol
O
R
phenoxide
OH
O
harder to deprot.
than carboxylic
acids - will deprot.
with NaOH
 Phenolic Protons
pKa approx. 10
amine
ammonium ion
H
R
 Amines
N
R
R
pKb approx. 5
will protonate
R
with strong and
moderately strong acids
N
R
R
O

Acidic drugs
O
OH
O
O
CH3
O
aspirin
NaOH
O
O
CH3
O

Phenolic containing drugs
O
OH
NaOH
O
O
THC
Would require much stronger base to do this.


Many drugs are alkaloids (Nitrogen containing bases).
Often these drugs are available as an acid salt (such as
the hydrochloride or sulfate), but the "free base" can be
obtained by deprotonation.
N
CH3 O
Cl
H
OCH3
O
cocaine
O
(free base = crack)
N
CH3 O
HCl
OCH3
NaOH
O
cocaine HCl
O
common
alternative
way of writing
pseudoephedrine
diphenhydramine HCl
LSD
mescaline
morphine sulfate

Water solubility of molecules is pH
dependent

A series of extractions and separations
is performed to effectively separate
compounds from a mixture:
▪
▪
▪
▪
▪
▪
Strong Acids
Weak Acids
Strong Bases
Weak Bases
Amphoteric Molecules
Neutral Molecules
http://orgchem.colorado.edu/hndbksupport/ext/extprocedure.html
White powder (caffeine + procaine) is added to methylene chloride
(CH2Cl2) in a separatory funnel.
Aqueous acid (such as 0.1 M H2SO4) is added.
▪ The caffeine molecule (neutral) is partitioned into the methylene
chloride (bottom, organic) layer.
The sulfate salt of procaine is partitioned into the aqueous (top) layer.

stays soluble in CH2Cl2
O
O
2
H2N
O
N
+ H2SO4
2
H2 N
O
water soluble
N
H
SO42-

The bottom layer is drained

the methylene chloride can be evaporated to obtain nearly pure caffeine.

Another portion of methylene chloride is added to the separatory funnel,
which still contains the aqueous acid and dissolved procaine.

Solid or aqueous base is added to the aqueous phase until that phase is
basic.

The procaine, converted to free base, is partitioned into the methylene chloride
(bottom) layer. O
O
2
O
N
H
H2N

+ 2NaOH
2
H2N
O
N
soluble in CH2Cl2
The bottom layer is drained

the methylene chloride can be evaporated to obtain nearly pure procaine.
Quinine Bisulfate is an Antimalarial Drug
Qunine is also found in tonic water
Quinine is fluorescent
H
HO
N
H
CH3O
H
HSO4
-
N
HO
2NaOH
CH3O
+ SO42- + 2H2O
N
N
If we titrate a known volume of quinine bisulfate solution with a
standardized (known molarity) NaOH solution, we can determine
the molarity of the quinine bisulfate solution.





Learn how to standardize a solution by
titration
Learn how to perform multiple titrations with
good precision
Review stoichiometry
Determine the concentration of a solution of
quinine bisulfate of unknown molarity
Observe the differences in solubility between
an acidic and basic form of a drug

Standardize
NaOH against KHP
O
O
O
NaOH
K
O
OH
+ H2O
O Na
O

K
O
Use standardized NaOH to titrate quinine
sulfate and calculate its molarity
H
HO
N
H
CH3O
H
HSO4
-
N
HO
2NaOH
CH3O
+ SO42- + 2H2O
N
N