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Extraction:

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- The transfer of a solute from one phase to another.

Carried out to: (1) isolate or concentrate the desired analyte; (2) Separate it from species that would interfere in the analysis.

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1. Partition Coefficient:

2. Fraction Remaining:

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1. K = [S]₂/[S]₁

2. K = [S]₂/[S]₁= ((1-q)m/V₂)/(qm/V₁)

q = V₁/(V₁ + KV₂)
After n extractions with volume V₂; qⁿ= (V₁/(V₁ + KV₂))²

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pH Effects on Extraction:

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If a solute is an acid or base, its charge changes as the pH is changed.
Usually a neutral species is more soluble in an organic solvent and a charged species is more soluble in aqueous solution.

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Extraction with Metal Chelator:

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Most complexes that can be extracted into organic solvents must be neutral.
Charged complexes, such as Fe(EDTA)^- or Fe(1,10-phenanthroline)₃²⁺, are not very soluble in organic solvents
Selectively complex one ion with an organic ligand and then extract it into an organic solvent.
Three ligands commonly employed are: Dithizone, 8-hydroxyquinoline, cupferron.

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What is Chromatography?

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Most powerful tool in an analytical chemist's arsenal for separating and measure the components of a complex mixture.
Process in which compounds areseparated from one another by passing them all through a column that retains some compounds longer than others.
Operates on same principle as extraction, but one phase is held in place while the other moves past it.

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Mobile phase:

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Either a liquid or a gas.
In gas chromtography, is a gas.
In liquid chromatography, is a liquid.

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Stationary phase-

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-Either a solid or a viscous liquid coated onto solid particles or onto the inside wall of a hollow capillary column.

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Eluent-

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-Fluid going in column.

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Eluate-

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-Fluid exiting column

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Packed column-

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Filled with particles containing stationary phase.

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Open tubular column:

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Narrow, hollow capillary with stationary phase coated on the inside walls.

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[Types of Chromatography]
Adsorption Chromatography-

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-Uses a solid stationary phase and a liquid or gaseous mobile phase: Solute is adsorbed on the surface of the solid particles.

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[Types of Chromatography]
Partition Chromatography-

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- Involves a thin liquid stationary phase coated on the surface of a solid support: solute equilibrates between the stationary liquid and the mobile phase.

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[Types of Chromatography]
Ion Exchange Chromatography-

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- Features ionic gropus such as -SO^3- or -N(CH₃)³⁺ covalently attached to the stationary solid phase, which is usually a resin: solute ions are attracted to the stationary phase by electrostatic forces; the mobile phase is liquid.

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[Types of Chromatography]
Molecular exclusion chromatography (Gel filtration)-

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-Separates molecules by size, with larger molecules passing through most quickly

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[Types of Chromatography]
Affinity Chromatography-

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Most selective kind of chromatography, employs specific interactions between one kind of solute molecule and a second molecule that is covalently attached to the stationary phase.

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Retention time, t_r-

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- For each component is the time needed after injection of the mixture onto the column until that component reaches the detector.

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Retention volume, V_r-

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- The volume of mobile phase required to elute a particular solute from the column.
;
- V_r = t_r * u_v

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Adjusted retention time, t'_r-

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-For a solute is the time requried for solute to travel the length of the column beyond the time required by unretained solvent, t_m.

t'_r = t_r - t_m

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Relative retention

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α = t'_r2/t'_r1
α will be > 1
greater relative retention, the greater the separation b/w two components.

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Capacity factor:

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k' = (t_r - t_m)/t_m
The longer a component is retained by the column, the greater the capacity factor.

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To monitor performance of a column, measure the:

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capacity factor for a standard
number of plates
peak symmetry
Changes above reflect degradation of the column.

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What two factors contribut to how well compounds are separated by chromatography?

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Difference in elution times between peaks; the further apart the better.
How broad the peaks are; the narrower the better.

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Resolution:

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Res. = Δt_r/w_av = ΔV_r/w_av
_{In quant. anal. a resolution of}> 1.5 is desirable.

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Plate Height:

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More theoretical plates, the narrower the bandwidth when the compound emerges.
The smaller the plate height, the narrower each eluted peak, and the better the separation.

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Factors Affecting Resolution:

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Doubling column length increases res. by √2
Res. increases as α; change the stationary phase in GC or either stationary phase or mobile phase in LC.
Res. increases as capacity factor increases. Increasing capacity factor is equivalent to increasing the fraction of time spent by the solute in the stationary phase.

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Advantages of Open Tubular Columns:

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Higher resolution
Shorter analysis time
Increased sensitivity
Lower sample capacity
Particles in packek column resist flow of the mobile phase, so flow rate cant be very fast
Open tubular column has higher linearflow rate for same length column
Allows for longer column that provides 100 times more theoretical plates.

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Van deemter Equation:

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H ≈ A + B/u_x + Cu_x

A- multiple paths
u_x - longitudnal diffusion
C- Equilibrium time
A, B, and C are constant for given column and stationary phase.
Packed column: A, B, C ≠ 0
Open Tubular Column: A = 0
Capillary electrophoresis: A = C = 0

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