Ch 21 – Principles of Chromatography and Mass

Spectrometry

Ch 22 – Gas and Liquid Chromatography

What is Chromatography? – Sec 21-1

Chromatography = a process where compounds in a mixture are separated by passing it through a column that retains some compounds longer than others

Mobile phase =

Stationary phase =

Elution =

Different Types of Chromatography

1. Adsorption chromatography

• stationary phase = solid (analyte adsorbs onto)

• mobile phase = gas or liquid

2. Partition chromatography

• stationary phase = thin liquid film coating inside surface of column or coats the solid support (SiO2)

• mobile phase = gas or liquid

3. Ion-exchange chromatography

• stationary phase = charged resin with covalently bound ionic groups such as -SO3

- or -N(CH3)3+; electrostatically attracts ionic analytes

• mobile phase = liquid

4. Molecular exclusion chromatography

• e.g. gel filtration, gel permeation, molecular sieve

• smaller molec ules trapped in pores while the larger ones elute faster

6. Affinity chromatography

• most selective, covalently bonded antibody binds a specific protein

How We Describe a Chromatogram – Sec 21-2

N = 5.55 tr2/W2

1/2

H = L/N

Theoretical Plates

Resolution = tr/Wav

1. Longitudinal Diffusion (B/u)

Why Do Bands Spread? – Sec 21-3

2. Equilibration Time (C·u)

3. Eddy Diffusion (A)

The Van Deemter Equation

Practical Control of Separation

• Find optimum flow rate (uopt)

• Decrease the stationary phase thickness

• Temperature programming increases Ds

• Choose carrier gas with higher Dm

• Decrease solid support particle size• Narrow-bore columns

Internal Standards – Sec 5-4

Area concentration

(Area X) / (Area S) unknown(Area X) / (Area S) standard

= [X] / [S] unknown [X] / [S] standard

X = unknown

S = standard

ASK YOURSELF (5-D, p. 103) - Using an Internal Standard

A mixture containing 52.4 nM iodoacetone (X) and 38.9 nm p-dichlorobenzene (S) gave the relative detector response (area of X)/(area of S) = 0.644. A solution containing an unknown quantity of X plus 742 nM S gave a relative detector response (area of X)/(area of S) = 1.093. Find the concentration of X in the unknown.

Gas Chromatography – Sec 22-1

• Sample volatilized and injected into a column along with an inert carrier gas or MOBILE PHASE

• Mixture separated by differential retention by the STATIONARY PHASE (some molecules hjeld up longer than others)

• Components separate according to boiling point (lowest first)

• Match analyte polarity to stationary phase polarity (“Like dissolves Like”)

Basic Instrumentation

The Injection Port

Capillary Columns

Capillary Columns

Stationary Phases

Temperature Programming

Detectors

A. Thermal Conductivity

B. Flame Ionization Detector (FID)

C. Electron Capture Detector (ECD)

Applications of Gas Chromatography

• Routine separation (e.g. after a synthesis)

• Identification of an unknown by comparing retention time to a known standard

• Quantization using an INTERNAL STANDARD

Example Separations

A. Environmental – EPA Methods

B. Biological