5.2 Notes

Organic Analysis

Pg. 119-136

Three chromatographic processes are used

1. Gas

2. High-Performance Liquid Chromatography

3. Thin-layer chromatography

Gas Chromatography (GC)

Separates mixtures on the basis of their distribution between a stationary liquid phase and a moving gas phase

Widely used because of its ability to resolve a highly complex mixture into its components with a few minutes

Moving phase is a gasCalled carrier gasMoves through a column of stainless steel

or glass with the liquid contained within the capillary column

Stationary phase is a thin film of liquid contained with the columnSimplified scheme = Figure 5-5, pg. 128

GC Scheme

Carrier gas is fed into the column at a constant rateCarrier gas = inert, generally nitrogen

or helium

Sample is injected as liquid into a heated injection port with a syringeImmediately vaporized and swept into

the column by the carrier gas

GC Scheme cont.Column is heated to keep the sample in vapor formComponents of the sample travel in the direction of the carrier gasSpeed determined by their distribution

between stationary and moving phases

Components become separated as they emerge from the column

GC Scheme cont.

As each component emerges from column, it enters a detectorDetector uses a flame to ionize the emerging chemicalGenerating an electrical signal recorded onto a strip chartSignal is recorded onto a strip-chart recorder as a function of time

ChromatogramWritten recorda plot of the results over time with each peak representing a component of the mixture time is called retention time

Advantage to GCExtremely sensitiveYields quantitative results

Pyrolysis

solid materials are heated to high temperatures so they decompose into numerous gaseous products

Gaseous product is entered into carrier gas stream and run through normal GC

5.2 Notes continued

High-Performance Liquid Chromatography

(HPLC)Moving phase liquid phase Unknown sample injected in the column

and carried by the liquid phaseDifferent components are retarded to

different degrees depending on their interaction with the stationary phase

Takes place at room temperatureUsed for organic explosives, heat sensitive drugs (LSD)

Thin Layer Chromatography (TLC)Solid stationary phase and moving liquid phase Glass plate covered with silica gel or

aluminum oxide, which serves as the solid stationary phase

Plate placed upright into a closed chamber that contains a selected liquid

TLC cont.

Liquid rises up the plate in a moving phase Separation occurs at point when components with a greater affinity for moving will move up the plate faster

TLC cont.Most results are colorless, materials must be visualizedPlates placed under UV light revealing

materials that fluoresceFluoresce = emit visible light when exposed to

a light of shorter wavelength

Distance travelled is known at Rf value which means the distance traveled by the

component divided by the distance traveled by the moving liquid phase

Electrophoresis

Separates materials according to their migration rates on a stationary solid phaseRelated to thin-layer chromatography

Electrical potential is placed across the stationary mediumMedium = starch or agar gel coated onto a

glass plate

Electrophoresis

Used for complex biochemical mixturesProteins

Enzymes in blood

DNA in dried blood

Separated proteins stained for visible observation

In-Class Assignment/Homework

5.2 Reinforcement Questions