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 Acids

Phenolic Protons

Amines

OH

O

RpKa approx. 5

will deprotonate with NaOH and moderately strong bases

carboxylic acid carboxylate

O

OR

OH

harder to deprot. than carboxylic acids - will deprot. with NaOH

pKa approx. 10

O

phenoxidephenol

will protonate with strong and moderately strong acids

R R

R

N

HR RN

R

pKb approx. 5

amine ammonium ion

Examples

Acidic drugs

O

O

CH3

OHO

O

O

CH3

OO

NaOH

aspirin

Examples

Phenolic containing drugs

O

OH

THC

NaOH

O

O

Would require much stronger base to do this.

Examples

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.

CH3

O

O

O

OCH3

NH

Cl

cocaine HCl

commonalternative way of writing

CH3

O

O

O

OCH3

N

cocaine (free base = crack)

HCl

NaOH

Examples

diphenhydramine HCl

pseudoephedrine

LSDmescaline

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.

H2N

O

ON

+ H2SO4

H2N

O

ON

H2 2SO4

2-

water soluble

stays soluble in CH2Cl2

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.

The bottom layer is drained the methylene chloride can be evaporated to obtain nearly pure procaine.

H2N

O

ON

H2H2N

O

ON

2+ 2NaOH

soluble in CH2Cl2

Titration of Quinine Bisulfate

2NaOH CH3O

N

HO

H N

+ SO42- + 2H2O

CH3O

N

HO

H N

H

HSO4-

Quinine Bisulfate is an Antimalarial DrugQunine is also found in tonic waterQuinine is fluorescent

If we titrate a known volume of quinine bisulfate solution with a standardized (known molarity) NaOH solution, we can determinethe molarity of the quinine bisulfate solution.

Objectives

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

Procedure (refer to handout)Standardize NaOH against KHP

Use standardized NaOH to titrate quinine sulfate and calculate its molarity

O

O K

O

OH

O

O K

O

O Na

NaOH

+ H2O

2NaOH CH3O

N

HO

H N

+ SO42- + 2H2O

CH3O

N

HO

H N

H

HSO4-