Lecture 10 - Gas Chromatography

GAS

CHROMATOGRAPHY

MMS 3201

AQUATIC METHODOLOGY AND

INSTRUMENTATION

Izwandy Idris, Blue Cabin,

ext. 3467, [email protected]

Introduction What is Chromatography?

Separation of compounds (solutes) into separate

components for identification (qualitative) and

concentration determination (quantitative)

Several techniques including such as Thin Layer,

Size-exclusion, HPL and Gas Chromatographies.

Gas chromatography – separating and analysing

volatile compounds that can be vaporized without

decomposition

GAS CHROMATOGRAPHY

Suitable for volatile and thermally stable (<450 oC) compound

Application in aquatic science: detection of Disinfection by-Products, taste odour components, insecticides, pesticides, hydrocarbon, fatty acids etc.

Sample of organic compounds is injected into an inert gaseous mobile phase (known as the carrier gas) for analysis.

The sample is carried through a packed or capillary column and the components in the sample are separated based on their ability to distribute between the stationary phase and the mobile phase.

GC analytical technique

2. Separation processes

i. Different adsorption with column packing

materials.

ii. Different Boiling point (Temp programming

System).

iii. Different in weight (Molecular weight)

A B C

The boiling points for

A=70oC B=100oC & C= 150oC.

If we increase the column temperature

from 60oC to 200oC at the rate of

10oC/min, the results of the

chromatogram will be

Peak

height

Time, min.

A B C

Carrier (inert) gas

Sample injected

(A, B &C)

Initial column temp set at 60oC

Retention Time, RT

INJECTION PORT

GC SEPARATION

Common inert mobile phase – Neon (Ne), Argon (Ar), Helium (He) and Nitrogen gas (N2)

Inert gas – no chemical reaction with mobile phase (compound) and stationary phase.

Chromatography column – two types i.e. packed and capillary

Capillary Columns

A.k.a open tubular column - made from fused silica coated with a protective polymer.

Up to 100 meter, diameter 50 – 300 m.

Types of Columns for GC

TYPES OF GC COLUMN

(0.01 –0.053cm)

(0.3-0.4cm)

Types of Columns for GC

Packed Column

• Made from glass, stainless steel, copper or aluminum, typically 2 – 6 m long, internal diameter 2 – 4 mm.

• Filled up with particulate solid with diameter ranging between 30-350 m. Smaller solid particle, > separation

TYPES OF GC COLUMN

(0.01 –0.053cm)

(0.3-0.4cm)

Comparison Of column

Capillary column Packed column

Capillary Column (Shimadzu 2010)

The Stationary Phase

Use high molecular weight, thermally stable

polymer, and chemically inert

Coating the inner tube (capillary) or solid support material

Solutes with different of boiling points are easily separated. Two solutes with the same boiling points could be separated if the stationary phase reacts with one of the solutes

Optimal detection – similar polarity with solute (increase separation and absorption)

Non-polar solutes – easier separation with non-polar stationary phase

Injection of Sample

1. Sample must be volatile.

2. The analyte must be present at an appropriate concentration.

3. Injected sample must not be degradable in the column.

Temperature Control (Temp Programming)

Important for good separation

Column inside a thermo-stated oven

Isothermal separation – column is

maintained at a constant temperature

Multi separation – temp is set slightly below

the lowest boiling solute and increase

gradually (Temperature programming)

1. Thermal Conductivity Detector

◦ based on mobile phase’s thermal conductivity

◦ Helium is selected mobile phase – high thermal conductivity

◦ When a solute is eluted from the column, the thermal

conductivity of the mobile phase decreases – change in

conductivity

◦ TCD gives a signal for any solute which has different thermal

conductivity from helium

◦ Can be used to detect any compound

DETECTORS FOR GC

2. Flame Ionization Detector (FID)

◦ Combustion of organic compounds in H2/air flame - flame

rich in electrons and ions.

◦ Ions are detected with electrically charge metal detactor (DC:

~300 v), more current across detector – high rate of

ionisation – high concentration

◦ used only for organic compounds

◦ Sensitivity is 2 – 3 lower than the TCD.

DETECTORS FOR GC

3. Electron Capture Detector (ECD)

◦ consists of a beta emitter (electron) such as 63Ni.

◦ Emitting electrons ionize the mobile phase (usually N2), production of additional electrons – electric current

◦ When the eluted solute pass through the ECD, the electric current in the ECD decrease and a signal is obtained

◦ Selective detector for solutes with electronegative functional groups (halogenated compounds and nitrogen groups) – pesticides (environment), pharmaceutical.

DETECTORS FOR GC

/Hydrocarbons

OM

OM

N2

H2 + O2

Example of Chromatogram-Petroleum

Hydrocarbon Analysis

Petroleum hydrocarbons are extracted from sea water and fractionated into

1. Aliphatic hydrocarbon &

2. Aromatic hydrocarbon fractions using

Column Chromatography.

GC-FID with capillary column (30 m) and temperature programming – 20 min (70 oC), increase to 300oC with a rate of 8oC/min and hold at 300 oC for 30 min

Aliphatic Hydrocarbons

min0 10 20 30 40 50 60 70

pA

50

100

150

200

250

FID2 B, (JOHNSON\SIG11155.D) C

8

C9

C10

C16

C17

IS

TD

i C

18

C19

C20

C21 C

22 C

23

C24

C26

C27

C28

C29

C32

Polyaromatic Hydrocarbons

min0 10 20 30 40 50 60 70

pA

20

40

60

80

100

120

FID2 B, (JOHNSON\SIG11026.D)

IS

TD

I

IS

TD

II

Pyr

IS

TD

III

BaA

BkF

BbF

IP

Qualitative & Quantitative Analysis

1. Use Reference Standard Material – such as

EPA 16 Aromatic Hydrocarbons

2. RSM is analyzed with the GC under the

same condition set for the analysis.

3. RT value and the intensity of peak are

recorded

4. Compare with the sample’s peak

Retention Value(RT) – 11.9 minutes

Aliphatic Hydrocarbons External Standard

min0 10 20 30 40 50 60 70

pA

100

200

300

400

500

600

FID2 B, (JOHNSON\SIG11151.D)

C8

C9

C10

C11

C12

C13

C14

C15

C16

C17

C18 C

19

C20

C21

C22

C23 C

24

C25

C26

C27 C

28

C29

C30

C32

Polyaromatic Hydrocarbons External Standard

min0 10 20 30 40 50 60 70

pA

50

100

150

200

250

300

350

400

450

FID2 B, (JOHNSON\SIG11032.D)

Na

Ace

Acy

Flu

Ph

An

FI

Pyr

Chy

rs B

aA

BkF

BbF

BaP IP dB

ahA

Bgh

iP

1. Sample with unknown solutes

2. Effluent from GC is introduced into the mass spectrometer’s ionization chamber – mobile phase removal

3. Ionization chamber – ionization of molecules and separated by mass to charge ratio

4. Selective monitoring detector is used to detect the specific mass-to-charge ratio produced electricity current

GC-MS (Identification of Organic Compounds)

GC MS(Shimadzu 2010)

GC-MS FLOW DIAGRAM

GC – MS 3D VIEW

Gas Chromatograph – Mass Spectrometer

Total Organic Carbon Analyzer

(TOC) Analysis of organic substances in

- Water

- solid including tissues and sediment

IR light absorption

Organic + O2 CO2

Infrared Analysis

600oC

TOC

Video on Gas Chromatography

https://www.youtube.com/watch?v=08YWhLTjlfo