Intro to Analytic Separations

Transfer of a solute from one phase to another

K ≈ [S]2 / [S]1 = As2 / As1 where S is the solute and A is the activity

qn = (V1 / (V1 + KV2))n where k is the partition coeffiecent V is the volume of each solute in eeach phase and n is the number of extractions

organic solvents

aqueous solvents

a Metal Chelator

D = (Total concentration in phase 2 / Total concentration in phase 1)

pH and ligand concentration

A technique in which molecules in a mobile phase are separated b/c of different affinities for a stationary phase. The high the affinity for the stationary phase the longer it stays on the column.

is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or dissolved solids to a surface

the solvent moving through the column (either a liquid or a gas)

Stays in place inside the column (usually a viscous liquid bonded to the column)

fluid entering the column

fluid emerging from the column

Process of passing a liquid or gas through a chromatography column

column filled with particles of stationary phase

a narrow hollow capillary with stationary phase coated to the walls

A solid stationary phase and either a liquid or gaseous mobile phase is used. Solute is adsorbed on the surface of solid particles. The more strongly adsorbed, the slower it travels trough the column.

A liquid stationary phase is bonded to a solid surface. Solute equilibration between the stationary liquid and mobile phase (usually flowing gas)

Anions or cations are covalently bonded to the stationary phase (usually a resin). Solute ions of the opposite charge are attracted to the stationary phase. The mobile phase is a liquid

Separates molecules by size, larger solutes pass through more quickly. Ideally there is no attraction between stationary phase and solute, but small pores in the stationary phase trap small molecules retaining them longer.

The most selective chromatography employs a specific interaction(s) between the solute and a second molecule covalently attached to the stationary phase. Ideally only one molecule will attached all others are washed away. The desired solute is dislodged by changing pH or ionic strength.

Equilibrating between 2 phases

When the RATE from phase1 to phase2 is equal to the RATE from phase2 to phase1.

mL of solute per minute

how many cm are traveled per minute

a graph showing detector response as a function of elution time.

time that elapses between injection and arrival at detector

volume of mobile phase required to elute a particular solute from the column

additional time required to travel the the length of the column beyond that of the mobile phase

T'r = Tr - Tm

for 2 components 1 ,and 2 relative retention is the ratio of their adjusted retention times

a = (T'r2 / T'r1)

the greater the separation between two components

time required to elute the peak minus Tm (for mobile phase)

k = (Tr-Tm)/Tm

the bigger k gets

(ΔTr / W avg) = (ΔVr / W avg) = (0.589ΔTr / W half avg) = (√N/4)(γ-1)

Tr = retention time
W = width of band
N = number of theoretical plates
γ = unadjusted relative retention

How close two bands in a spectrum or chromatogram can be to each other and still be seen as two peaks

transport of a solute from high to low concentration, can cause band spreading

((16*Tr^2) / (w^2)) = ((5.55*Tr^2) / (w^2)) = ((tr^2)/ σ^2))

H = L / N

L = length of column
N = number of theoretical plates

the narrower the band width,
the sharper the peaks,
the better the separation,
etc

theoretical plates

H = L/N = σ^2/x

L =length
N = number of plates
σ = stdev of the band
x = distance traveled

σ = √2Dt

D = diffusion coefficient
t = time

It's narrow

1) Plate height, H
2) Linear flow rate, μx

H ≈ A+ (B/μx) + (Cμx)

A = multiple paths
B/μx = Longitudinal Diffusion
Cμx = Equilibration time

Diffusional broadening of a band occurs while the band is transported along the column; the faster the linear flow the less time spent in the column and the less diffusional broadening occurs

comes from the finite time required to equilbrate between stationary and mobile phases

it essentially says that van Deemter (which is a measure of plate height) is BOTH proportional and inversely proportional to linear flow rate

An isotherm is a graph of cs vs. cm at a given temperature. If the isotherm is not linear, peak distortion may occur in the chromatogram (ie., tailing or overloading)

-treatment of column surface silica or stationary phase particles with nonpolar trimethylsilyl groups.
-used to reduce tailing by blocking hydroxyl groups that may otherwise bind solute strongly