GC .pdf

1
Sigma Aldrich Analytical Basic Techniques
Webinar series
Webinar two
The Basics of Gas Chromatography

2
Basic Theory
Capillary GC Columns, Defining Parameters
The Stationary Phase
Capillary Column Types Available and a few
Applications

3
What is Gas Chromatography?
•A technique in which separation is accomplished by partitioning
volatilized substances between a mobile carrier gas and a
stationary phase. The technique is often termed “GC.”
•GC is done using an instrument called a gas chromatograph (also
called a GC.)
•The separation is done on a column, which is contained in the
oven of the gas chromatograph.
•There are two types of GC columns, packed and capillary.

4
A Simple
Analogy
A zoo train derailed
over a river. Monkeys,
elephants and cows
were free!

5
A Simple
Analogy
The animals drifted by an
island that had bananas,
grass and peanuts. Each
animal stopped at their
favorite food. They each
took their time eating before
setting off.

6
A Simple
Analogy
Eventually, the animals
floated under a bridge.
As the animals went
under the bridge, the
“detector” called out the
time and the number of
each animal.

7
The caretakers
graphed the detector’s
data. They plotted the
number of each animal
on the y-axis and the
time it passed under
the bridge on the x-
axis.
TIME (hours)
CO
UN
T
A Simple Analogy

8
Why would a scientist use GC?
An analyst would choose GC when they want to know the
composition of a sample and any of the following:
They are following a specified method that uses GC (EPA, USP, etc.)
Their compounds are volatile or can be made volatile by derivatization,
thermally stable and low molecular weight (<800amu)
They can’t use HPLC because the compound lacks a chromophore or has
no HPLC retention

9
Gas Chromatography
Components of the Gas Chromatograph
A GC consists of a regulator, column, carrier gas, injector, and
detector. The column can be a tube packed with particles, or a
capillary with stationary phase coated on the walls.
Types of samples
They must be organic, thermally stable and able to be volatilized.
Typical carrier gases
Inert gases (He, H2, N2) are used at temperatures up to 400°C.
Other gases such as CO and Ar have also been used.

10
Components of a GC system
1. Gas supply for carrier gas (cylinder, generator)
2. Injector (injector port)
3. Oven with the column
4. Detector
5. Data Aquisition System (PC or Recorder)
More details on the
next slide

11
Cut-away of a GC injection port
From http://www.shsu.edu/~chemistry/GC/packed.GIF

12
Capillary GC columns:
• Modern technology
• High efficiency
• Usually flexible glass fibers (fused silica),
<1mm ID
• Coated phase: Organic polymers dissolved
in solvent and coated on the inside wall of
the tubing
Packed vs. capillary GC columns
Packed GC columns:
• First type of GC column
• Low efficiency
• Glass, stainless steel, nickel, copper or Teflon
tubing, 1/16” – 1/4” OD
• Coated phase: Organic polymers dissolved in
solvent and coated onto the particles
• Siliceous particles: diatomaceous earth for
supporting coated phase
• Adsorbent particles: molecular sieve, carbon,
polymers
All GC columns are open tubes. In packed column GC, the tubes are
>1mm ID and the separation phase is coated on particles packed in the
tube. In capillary GC, the tubes are <1mm ID and the separation phase is
coated on the inside of the capillary wall.

13
GC column installed in an oven
From the injection port
To the detector
Column coils

14
Parts of a capillary GC column
• Protective layer
• Usually polyimide
• Gives the tube flexibility so it does not break easily
• Tube
• Usually fused silica, like a hollow fiber-optic fiber.
• Inside surface should be inert or deactivated to prevent adsorption
• Length typically 5 to 150 meters
• ID from 0.1 to 0.75 mm
• Phase layer
• An organic or organosilane polymer or
small particles coated on the inside
layer of the tube
• What gives the column its selectivity
• Thickness of the phase layer (df) can be
from 0.1 to 0.70 µm

15
Types of GC detectors
•Universal
• MSD (mass spectrometry): ID compounds based on m.w. of fragments and
fragmentation pattern. MS is becoming affordable to most labs.
• TCD (thermal conductivity): ID compounds based on differences in their
conductance of heat
•Selective
• FID (flame ionization): C-C or C-H bonds
• ECD (electron capture): Halogens (Cl, Br, F)
• SCL (sulfur chemiluminescence): Sulfur-containing cpds.
• NPD (nitrogen/phosphorous)
• FPD (flame photometric): Sulfur, phosphorous
• PID (photoionic): Aromatics
• ELCD (electrolytic conductivity): Chlorinated hydrocarbons
Many different GC detectors are available. Some are universal in that nearly all
compounds will give some signal. Some are selective or specific to a class of
compound or chemical bond.

16
Photo of a typical GC set-up
Agilent 6890N
Column oven
Injection port
Controller
Carrier gas regulators
(attached to wall behind instrument)
PC (User interface)
Detector
Sample rack
Autosampler

17
The Chromatogram (Output)
Capillary Column
GC Chromatogram
1
2
4
5
Conditions

18
min
0 5 10
VWD1 A, Wavelength=254 nm (QCTESTSTHYDAP0.D)
Separation Terminology
Resolution:
distance between peaks Efficiency:
width of the peak
Retention:
time each peak elutes
Symmetry:
shape of the peak

19
Capacity (k’)
• Also known as the retention factor.
• It is a measure of retention by the stationary phase.
• It is calculated as follows:
k’ = tr-tm/tm
Where: tr = retention time of analyte
tm = retention time of an unretained compound
K is really a unit of time. The smaller the k value the closer the analyte elutes
to the dead time of the column. The dead time measures how long it takes
an unretained solute to reach the end of the column.
For example, methane can be used in most silicone coated columns and can
easily be detected by FID to measure dead time.

20
Selectivity
•Selectivity is related to α, the separation factor. α should be large enough to give
baseline resolution, but small enough to prevent waste (time and gas).
0 5
Measuring α
α
α
α
t r1
tr2
tr3
tm
Measuring α
α
α
α α
α
α
α2/1 = k’2/k’1
How we provide
selectivity: wide variety
of GC phases. Unlike
LC, the mobile phase
does not contribute to
the selectivity of the
column.

21
10
tr
N = 5.545 x (tr/wb1/2 )2
wb1/2
Measuring Peak Efficiency
•Narrow peaks have high efficiency, and are desired.
•Units of efficiency are “theoretical plates” (N) and are often used to describe
column performance.
•“Plates” is the current common term for N.
Low N peaks are caused by many factors, but dead volume and fouled or
poorly coated columns are the most common.

22
10
Measuring Peak Symmetry
• Symmetrical (a=b) peaks are desired.
• Unsymmetrical peaks are often described as “tailing” or “fronting”.
• Tailing may be caused by inlet conditions, improper column
installation or a poorly deactivated column.
• Fronting generally occurs when to much solute has been injected
overloading the capacity of the stationary phase.
a b
AF10 = b/a

23
Resolution (R) is
another term for the
distance between two
peaks.
Resolution over a
value of 1.5 may be
considered a waste
of time.
An R value of 1.5 is baseline separation.
Resolution

24
The Mobile Phase
One thing that makes GC very different than LC is the limited number of
mobile phases. The two basic capillary mobile phases are Hydrogen and
Helium.
The mobile phase in GC is more commonly called the carrier gas.

25
Van Deemter Plots
Hydrogen
Helium
Nitrogen
Air
Golay plots or Van Deemter plots tell
us a lot concerning selection and
appropriate use of the carrier gas.
Ideally, analytes should hit the column
in a narrow ‘plug’ to produce sharp
peaks.

27
Length (L)
•Increasing length:
• Increases retention
• Increases N
• Requires higher headpressure
• Will not affect selectivity
• Only nominally increases resolution
• Increases column bleed

28
Inside Diameter (ID)
•Decreasing inner diameter:
• Decreases sample capacity – reduced the quantity of stationary
phase
• Requires higher head pressure
• Increases resolution by increasing N

29
Film Thickness (df)
•Increasing film thickness:
• Increases retention
• Increases sample capacity
• Increases column bleed
• Increases inertness (usually)
• May increase resolution
• Requires higher headpressure
• Increases resolution by increasing N

30
Choosing Column Dimensions
The Capacity Trade Off
Some analysis may require a column that
provides more capacity due to sample, injection
techniques or detector limitations. In these cases,
a column of greater film thickness or ID may be
better suited for the analysis at the expense of
efficiency and time.

32
Types of capillary GC phases
• Non-polar phases
• Separation by boiling point
• Common non-polar phases:
–“1” – poly(dimethyl)siloxane
–“5” – poly(5% diphenyl, 95% dimethyl)siloxane

MOST COMMON NON-
POLAR PHASE
• Polar phases
• Separation by additional polar interactions with the phase
• Common polar phases:
–SUPELCOWAX 10 – poly(ethylene glycol)

MOST COMMON POLAR
PHASE
–“35” – poly(35% diphenyl, 65% dimethyl)siloxane
–“1701” – poly(14% cyanopropylphenyl, 86%-dimethyl)siloxane
Capillary GC columns are available with a wide variety of stationary phases. The
phases are generally classified as non-polar and polar.

33
Polarity ranking of Supelco GC phases
SPB-Octyl Nonpolar
Equity-1, SPB-1
Supelco SLB-5ms, Equity-5, SPB-5
SPB-20
SPB-35
Equity-1701, SPB-1701
SPB-50/SP-2250
SPB-225
PAG
SUPELCOWAX 10
SPB-1000/Nukol
SP-2330
SP-2380
SP-2340 Very polar
Supelco offers a full range of non-polar and polar, specialty and general purpose GC phases.
Choose “5” type phases for most
non-polar analytes
Choose wax type
phases for most
polar analytes

34
Importance of low-bleed character
• All components of the GC system, but especially columns, should be low-bleed.
• Bleed can interfere with the analysis and reduce sensitivity.
• Bleed ions can also interfere with qualifier ions in GC-MS detection, reducing the
reliability of the analysis.
• Extreme bleed can damage the instrument.
• The chromatograms below show Supelco SLB-5ms ultra-low bleed columns
compared to competitive columns.
16.00 17.00 18.00 19.00 20.00 21.00 22.00 23.00 24.00
0
200000
400000
600000
800000
Time--
Supelco SLB-5ms
Higher bleed competitive 5ms columns

35
Special Purpose Columns
Developed for a specific application
Tested specifically for an application
Guaranteed performance for an application
Sometimes they contain the same phase as general purpose columns (such as
SLB-5)
Examples of special purpose columns include the SPB-1Sulfur, and Petrocol
DH150.

USEPA Method 8081 Chlorinated Pesticides (GC)
0 10 20 30 40 50
Time (min)
1
2
3
4
5
6
7
8 9
10,11
12,13
14
15
16
17
18,19
20
21
22
Column: Equity-5, 30m x 0.25mm ID, 0.25µm (Cat. No. 28089-U)
Oven: 100°
C (2 min.) to 160°
C @ 15°
C/min. to 300°
C @ 5°
C/min. (10 min)
Inj.: 225°
C
Det.: ECD, 310°
C
Flow: Helium, 30 cm/sec. @ 100°
C
Injection: 2.0µL, splitless (0.5 min.)
Liner: Splitless double taper, unpacked
Sample: 50ppb of a 22 component chlorinated pesticide standard (Cat. No. 46845-U)
1. 2,4,5,6-Tetrachloro-m-xylene (surr.) 12. 4,4'-DDE
2. alpha-BHC 13. Dieldrin
3. beta-BHC 14. Endrin
4. gamma-BHC 15. Endosulfan II
5. delta-BHC 16. 4,4'-DDD
6. Heptachlor 17. Endrin aldehyde
7. Aldrin 18. Endosulfan Sulfate
8. Heptachlor epoxide 19. 4,4'-DDT
9. gamma-Chlordane 20. Endrin ketone
10. Endosulfan I 21. Methoxychlor
11. alpha-Chlordane 22. Decachlorobiphenyl (surr.)
Stable Baseline, No Bleed
Excellent Peak Shape and Resolution

USEPA Method 8082 Polychlorinated Biphenyls (GC)
12 14 16 18 20 22 24 26 28
Time (min)
1
2
3
4
Oven: 100°
C (2 min.) to 160°
C @ 15°
C/min. to 300°
C @ 5°
C/min. (10 min)
Inj.: 225°
C
Det.: ECD, 310°
C
C
Liner: Splitless double taper, unpacked
Sample: Aroclor Mix 1 standard at 75ppb with surrogates at 7.5ppb. (Cat. No. 46846-U)
1. 2,4,5,6-Tetrachloro-m-xylene (surr.), 7.5 ppb
2. Aroclor 1016, 75 ppb
3. Aroclor 1260, 75 ppb
4. Decachlorobiphenyl (surr.), 7.5 ppb
Stable Baseline, No
Bleed

Diesel Fuel (GC)
0 10 20 30 40
Time (min)
3pA @ 325°
C
Oven: 40°
C (4 min.) to 325°
C @ 8°
C/min.
Inj.: 275°
C
Det.: FID, 325°
C
Flow: Helium, constant flow, 1.2 ml/sec. @ 40°
C
Injection: 1.0µL, split 200:1
Liner: 4mm ID single taper
Sample: 100ng on-column of a No. 2 Fuel Oil standard (Cat. No. 47515-U)
Excellent Peak Shape and Response
Low FID Bleed

Simple Hydrocarbons (GC)
10 20 30 40
Time (min)
10 20 30 40
Time (min)
Equity-1
Equity-5
1
2
3 4 5
6 7
7 9 10
11
12 13
14
15
16
17
1
2
3
4 5
6 7
8
9
10
11
12 13
14
15
16
17
Column 1: Equity-1, 30m x 0.25mm ID, 0.25µm (Cat. No. 28046-U)
Oven: 40°
C (8 min.) to 325°
C @ 12°
C/min. (16 min.)
Inj.: 275°
C
Det.: FID, 325°
C
Flow: Helium, constant flow, 1.2 ml/sec. @ 40°
C
Liner: 2mm ID splitless
Sample: 100ng on-column of a 17 component n-hydrocarbons standard (Cat. No. 46855-U)
1. C8
2. C10
3. C12
4. C14
5. C16
6. C18
7. C20
8. C22
9. C24
10. C26
11. C28
12. C30
13. C32
14. C34
15. C36
16. C38
17. C40
4pA @ 325°
C
2pA @ 325°
C
Low FID Bleed

1
2
3
4
5
6
7
8
9 10
11
12
13
14
15
16
1. Amphetamine
2. Methamphetamine
3. Nicotine
4. Caffeine
5. Diphenhydramine
6. Lidocaine
7. Phenobarbital
8. Methadone
9. Amitriptyline
10. Cocaine
11. Desipramine
12. Codeine
13. Morphine
14. Diazepam
15. Heroin
16. Fentenyl
Drug Screen (GC/MS)
Oven: 45°
C (2 min.) to 110°
C @ 25°
C/min to 200°
C @ 15°
C/min to 280°
C @ 6°
C/min (3 min.).
Inj.: 250°
C
Det.: 5973 MSD, 40-450 amu scan range, 325°
C transfer line
Flow: Helium, 40psi for 0.2min then 0.7mL/min constant flow
Injection: 0.3µl pulsed splitless @ 50mL/min (0.5min)
Liner: Splitless 2 mm ID
Sample: ~15ng on-column of a 16 component drug standard
Amphetamine: Excellent
Peak Shape and Response
Key resolution achieved
8.0
6.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0

Residual Solvents (GC)
0 10 20 30
Time (min)
1
2
3
4
5
6 7
8
9
10
11
12 13
14
15
16,17
18,19
20
21 22
23
24
DMSO(solvent)
Oven: 40°
C (6 min.) to 100°
C @ 2°
C/min.
Inj.: 225°
C
Det.: FID, 250°
C
C
Liner: Split, cup design
Sample: 5ng on-column of a 24 component solvent standard
1. Methanol
2. Ethanol
3. Acetonitrile
4. Acetone
5. 2-Propanol
6. Ethyl Ether
7. 1,1-Dichlorothylene
8. Freon 113
9. Methylene Chloride
10. Methyl-tert-Butyl ether
11. 2-Butanone
12. Hexane
13. Ethyl acetate
14. Chloroform
15. Tetrahydrofuran
15. 1,1,1-Trichloroethane
17. 1,2-Dichloroethane
18. Carbon tetrachloride
19. Benzene
20. Trichloroethylene
21. 1,4-Dioxane
22. 4-Methyl-2-pentanone
23. Toluene
24. Dimethylformamide

1
2
3
4
5
1. 2-Isopropyl-3-methoxypyrazine, 2 ppt
2. 2-Isobutyl-3-methoxypyrazine, 2 ppt
3. 2- Methylisoborneol, 2 ppt
4. 2,4,6 - Trichloroanisole (Internal Standard), 8 ppt
5. (±)Geosmin, 2 ppt
Trace Odors in Drinking Water (SPME-GC/MS)
Column: Equity-5, 30m x 0.25mm, 0.25µm film, Cat. No.: 28089-U
SPME Fiber: 2cm StableFlex coated with 50/30µm DVB/Carboxen/PDMS, Cat. No. 57348-U
Extraction: headspace, 65°
C (30 min.)
Desorption: 3 min. at 260°
C
Oven: 60°
C (2min) to 200°
C at 8°
C/min
GC Liner: 0.75mm SPME liner
Detector: 5973 MSD, selected ions (SIM) 95, 112, 124, 137, 197; interface at 280°
C
Flow: Helium, 37cm/sec@ 60°
C (1mL/min constant flow)
Injection: SPME fiber, splitless opened at after 1 min at 50mL/min.
Sample: 25mL of water containing 25% NaCl and drinking water odors kit, Cat. No. 46729-U
Excellent Analyte Response at 2 ppt
6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0

Bacterial Acid Methyl Esters (GC)
0 10 20 30
Time (min)
Solvent
Solvent
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21 22
23
24
25
26
Oven: 150°
C (4 min.) to 250°
C @ 4°
C/min. (5 min.)
Inj.: 250°
C
Det.: FID, 280°
C
C
Sample: 100ng on-column of a 26 component BAME standard (Cat. No. 47080-U)
1. Me. Undecanoate (C11:0)
2. Me. 2-Hydroxydecanoate (2-OH-C10:0)
3. Me. Dodecanoate (C12:0)
4. Me. Tridecanoate (C13:0)
5. Me. 2-Hydroxydodecanoate (2-OH-C2:0)
6. Me. 3-Hydroxydodecanoate (3-OH-C12:0)
7. Me. Tetradecanoate (C14:0)
8. Me. 13-Methyltetradecanoate (i-C15:0)
9. Me. 12-Methyltetradecanoate (a-C15:0)
10. Me. Pentadecanoate (C15:0)
11. Me. 2-Hydroxytetradecanoate (2-OH-C14:0)
12. Me. 3-Hydroxytetradecanoate (3-OH-C14:0)
13. Me. 14-Methylpentadecanoate (i-C16:0)
14. Me. cis-9-Hexadecenoate (C16:1)
15. Me. Hexadecanoate (C16:0)
16. Me. 15-Methylhexadecanoate (i-C17:0)
17. Me. cis-9,10-Methylenehexadecanoate (17:0)
18. Me. Heptadecanoate (17:0)
19. Me. 2-Hydroxyhexadecanoate (2-OH-C16:0)
20. Me. cis 9, 12-Octadecadienoate (C18:2)
21. Me. cis-9-Octadecanoate (C18:1)
22. Me. trans-9-Octadecanoate (C18:1)
23. Me. Octadecanoate (C18:0)
24. Me. cis-9,10-Methyleneoctadecanoate (C19:0)
25. Me. Nonadecanoate (C19:0)
26. Me. Eicosanoate (C20:0)

Distilled Lime Oil (GC)
0 10 20 30
Time (min)
0 10 20 30
Time (min)
Equity-1
Equity-5
1 2
3
4
5
6
7,8,9
10 11
12
13 14
15
16
17
18
19
20 21 22
23 24
25
26
27 28,29
1
2
3 4
5
6,7,8
9 10 11
12
13
14
15
16
17
18 19
20 21 22
23
24
25
26
27
28,29
Oven: 75°
C (8 min.) to 200°
C @ 4°
C/min. (10 min.)
Inj.: 250°
C Det.: FID, 250°
C
C
Injection: Wet Needle, split 100:1
Sample: Distilled lime oil
1. alpha- Pinene
2. Camphene
3. beta- Pinene
4. Myrcene
5. alpha- Phellandrene
6. 1,4-Cineole
7. alpha-Terpinene
8. p-Cymene
9. d-Limonene
10. gamma-Terpinene
11. Terpinolene
12. Linalool
13. alpha-Fenchyl alcohol
14. Terpinen-1-ol
15. beta- Terpineol
16. Borneol
17. Terpinen-4-ol
18. alpha- Terpineol
19. gamma- Terpineol
20. Decanal
21. Neral
22. Geranial
23. Neral Acetate
24. Geranyl Acetate
25. Dodecanal
26. beta-Caryophyllene
27. trans-alpha-Bergamotene
28. trans-alpha- Farnesen
29. beta-Bisabolene

Anilines (GC)
8 10 12 14 16 18 20 22 24
Time (min)
1
2
3 4
5
6
7
8
9
10
11
12
13
14
15
16
Oven: 50°C (2min) to 200°
C @ 10ºC /min. to 325°
C @ 15ºC /min.
Inj.: 250°
C
Det.: FID, 325°
C
Flow: Helium, Constant flow, 1.3 ml/sec @ 50ºC
Injection: 1.0 ul, splitless (0.5 min.)
Liner: Split less, 4mm ID single taper
Sample: 50ng on-column of a custom anilines mix
1. Aniline
2. 3-Aminobenzotrifluoride
3. o-Toluidine
4. N,N-Dimethylaniline
5. 2-Chloroaniline
6. 2,6-Dimethylaniline
7. 3-Chloro-4-Fluoroaniline
8. 4-Isopropylaniline
9. 2-Methyl-6-Ethylaniline
10. 4-Chloro-4-Methylaniline
11. 2,6-Diethylaniline
12. 2,4-Diaminotoluene
13. 3,4-Dichloroaniline
14. 2,4,5-Trichloroaniline
15. 4-Chloro-2-nitroaniline
16. 3,3'-Dichlorobenzidine
Low FID Bleed
3pA @ 325°
C

Indoor Air (GC/MS)
1
2
3
4
5 6
7
8 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
33
32
34
35
36
37
38
39
40 41
42
43
44 45
46
4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0
Oven: 35°
C (3 min.) to 100°
C @ 8°
C/min. to 250°
C @ 20°
C/min. (10 min.)
Inj.: 250°
C
Det.: MSD, Scan range 33-350 amu, 280°
C transfer line
Flow: Helium, 30 cm/sec @ 35°
C
Sample: 100ng on-column of the Japanese Indoor Air Standards Mix (Cat. No. 47537-U)
20. Octane
21. Tetrachloroethylene
22. Ethylbenzene
23. m-Xylene and p-Xylene
24. Styrene
25. o-Xylene
26. Nonane
27. alpha-Pinene
28. 3-Ethylbenzene
29. 4-Ethylbenzene
30. 1,3,5-Trimethylbenzene
31. 2-Ethyltoluene
32. beta-Pinene
34. Decane
35. 1,4-Dichlorobenzene
37. Limonene
38. Nonanal
39. Undecane
40. 1,2,4,5-Tetramethylbenzene
41. Decanal
42. Dodecane
43. Tridecane
44. Tetradecane
45. Pentadecane
46. Hexadecane
1. Ethanol
2. Acetone
3. 2-Propanol
4. Methylene Chloride
5. 1-Propanol
6. 2-Butanone
7. Hexane
8. Ethyl acetate and Chloroform
9. 1,2-Dichloroethane and 2,4-Dimethylpentane
10. 1,1,1-Trichloroethane
11. Benzene and 1-Butanol
12. Carbon Tetrachloride
13. 1,2-Dichloropropane
14. Bromodichloromethane, Isooctane, Trichloroethene
15. Heptane
16. 4-Methyl-2-pentanone
17. Toluene
18. Chlorodibromomethane
19. n-Butyl acetate

Phthalate Esters (GC)
14 16 18 20 22 24 26 28
Time (min)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Oven: 40°C (1 min.) to 325°
C @ 10ºC /min.
Inj.: 250°
C
Det.: FID, 325°
C
Flow: Helium, Constant flow, 1.3 ml/sec @ 40ºC
Injection: 1.0 ul, splitless (0.75 min.)
Liner: Splitless, 4mm ID single taper
Sample: 50ng on-column of a custom phthalate ester mix
1. Dimethyl phthalate
2. Diethyl phthalate
3. Benzyl benzoate
4. Diisobutyl phthalate
5. Dibutyl phthtlate
6. Bis(2-methylethyl)phthalate
7. Bis(4-methyl-2-pentyl)phthalate
8. Bis(2-ethoxyethyl)phthalate
9. Diamyl phthalate
10. Di-n-hexyl phthalate
11. Butyl benzyl phthalate
12. Hexyl-2-ethylhexyl phthalate
13. Bis(2-butoxyethyl)phthalate
14. Dicyclohexyl phthalate
15. Bis(2-ethylhexyl)phthalate
16. Di-n-octyl phthalate
17. Di-n-nonyl phthalate
Low FID Bleed
Excellent Peak Shape
3pA @ 325°
C

48
Important characteristics of GC
columns
• Low-bleed
• Columns and all accessories must not add contaminants to the carrier
gas. This adds noise that interferes with the sample and reduces the
sensitivity of the separation.
• Inert
• Columns and any part that comes in contact with the sample should be
inert; they should not adsorb the sample. Adsorption (lack of inertness)
causes poor peak shape and reduces the sensitivity of the separation.
• Efficient
• Columns and fittings should be designed to maximize efficiency, which
increases the sensitivity and resolution of the separation.
• Selective
• Columns should be available in phase chemistries that provide the user
choices in selectivity.

49
Advantages/disadvantages of GC vs. HPLC
•GC advantages over HPLC:
-GC is generally simpler to use
-GC instruments are usually less expensive
-GC is more universal; analytes do not have to have a chromophore
-GC has higher efficiency (resolves more compounds per unit time)
•HPLC advantages over GC:
-HPLC is more amenable to polar, non-volatile and thermally labile
compounds, like most biochemicals, drugs and metabolites
-HPLC has the power of the mobile phase to increase resolution
-HPLC is non-destructive and can be used for preparative separations

50
In the office
David Cheetham – UKAnalytical@sial.com custom items, 01202712374,
Fax 01747833584
Ben Kemp – eurtechserv@sial.com - technical queries 0800272572
Local Analytical Field Sales
Darren Cooke – London darren.cooke@sial.com 07768622053
Alan Farnaby – Midlands and East alan.farnaby@sial.com 07747773920
Paul Walsh – North England and Scotland paul.walsh@sial.com 07900814419
Jon Farkas-Blake (Team Leader) – Southwest and Wales
jonathan.farkas-blake@sial.com 07786272011
UK Sales Development
Lisa Fitzpatrick – lisa.fitzpatrick@sial.com 07831238988
Where to go for help….

51
Thanks for your attention!
The presentation will be available to download
from the Sigma Aldrich Analytical events
webpage after Friday 23rd Oct.

GC .pdf

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