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To separate solutes differing in vapor pressure

and/or intensity of solute-stationary phase interactions

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What are main components of

a gas chromatograph ?

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Gas chromatograph

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Mobile phaseCarrier gas: N2, He, H2

non-solvating, high purity, and chemically inertness

Thin filmThick film

Further purifying carrier gas by

humidity, hydrocarbon,and oxygen traps/filters

Pure He, N2(> 99.995%)

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GC

Gas-Solid Chromatogr. (GSC)Stationary phase: solid

Gas-Liquid Chromatogr. (GLC)Stationary phase: immobilized liquid

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Stationary phase: Al2O3, carbon

Less popular than GLC

Disadvantages : long retention times, tailing,

poor reproducibility from col. to col.

Main applications: gas analysis

GC stationary phase (GSC)

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GC stationary phase (GLC)

unreactive, high thermal stability

low vapor pressure good coating characteristics

wide temperature operating range

Features ofgoodliquid stationary phases for GLC

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What are stationary phases of GC ?

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High molecular weight hydrocarbons

- Squalane (C30H62) (shark liver oil)

Stationary phase (GLC)

- Apolane-87 (C87H176)

Proposed substitution of apolane-87 for squalane as a nonpolar reference

phase in gas chromatography Analytica Chimica Acta Vol. 225, 1989, 193-203

Squalane is the standard, nonpolar reference phase . SP in GLC ... Primaryobjections to its use as a reference phase are its high volatility, compositionalvariations due to the presence of impurities, susceptibility to oxidativedegradation, poor film forming. the synthetic hydrocarbon Apolane-87, its useas a reference phase is to be preferred.

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Poly (siloxane)

poly(siloxane)

polymer

poly(silarylene-siloxane)

copolymerpoly(carborane-siloxane)

copolymer

C

BH

Stationary phase (GLC)

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Stationary phases

Stationary phases can be deposited on to column walls by

cohesive or wetting forces

surface-bonded (bonded phase)

it may be cross-linked to produce a liner or envelope of

stationary phase polymer within the column it may be both cross-linked and surface-bonded

Cross-linking can produce a stationary phase that is non-extractable

(splitless, on-cloumn injection or washing the columns)

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Polarity

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Effect of stationary phase polarity on separation of

(i) An alkane and an ester of similar volatility (68 oC)

(ii) An alkane and 2 esters of different volatility (68 oC and 57oC)

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Packed and capillary column

Packed column Capillary column

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GC columns

Packed columns

1-3mm i.d.

< 5m length

0.1-0.4 mm dp

Capillary columns

0.1-0.33 mm i.d. (mega-bore 0.53 mm)

12-150 m length0.1 -0.5 m film thickness

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Porous LayerOpen

Tubular column

(PLOT)

Support Coated Open

Tubular column

(SCOT)

Wall Coated Open

Tubular column

(WCOT)

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Fused silica tube

0.10.5 mm i.d.

Chemically bonded phase0.1 - 5 m

Wall Coated Open Tubular column

(WCOT)

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Typical characteristics of GC columns

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Preparation of

capillary column

Furnace

Coater 1

Coater 2

Coater 3

Coater 4

Reel

Curingoven 3

Curingoven 2

Curingoven 1

Curingoven 4

(2300oC)

Fused silica

(Polyimide)

10m

tower

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Purity of silica and its strength

Fused silica

Modified silica

clean room conditions are required for preparation of fused silica !

thin-walled columns (0.20 mm ID x 0.25 mm OD) that were inherently straight,extremely strong, and highly flexible are made from fused silica.

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Column deactivation

C10C12 C17

1

2

3

4

5

6

C10C12

C17

3

1 3,5-dimethylpyrimidine 4 C10-NH22 C8-NH2 5 N,N- dicyclohexylamine

3 2,6-dimethylaniline 6 C12-NH2

before after

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Column thermal stability

g/min

Bleeding as a function

of temperature

Temperature

Standard bleed test

Thermally-induced catalytic stationary phasedecomposition due toalkali metal ions

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Scotch Whisky *

Packed Col. 5% Carbowax 20M on 80/120 Carbopack B (2 m 2 mm I.D.)FID; Temp. : 70C, 4C/min. to 150C

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Barley Malted barley

Scotch Whisky production

Malting mashing fermentation distillation maturation

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Distilled lime oil

-Fenchyl alcohol,-Phellandrene,-Pinene,-Bisabolene,-Caryophyllene,

-Terpinene, 1,4-Cineole, d-Limonene, p-Cymene, trans--Bergamotene, Borneol,

Camphene, Decanal, Dodecanal, Geranial, Geranyl acetate, Linalool, Myrcene, Neral,

Neryl acetate , Terpinen-1-ol, Terpinen-4-ol, Terpinolene,-Terpineol, natural, Kosher

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Column: SLB-5ms, 20 m x 0.18 mm i.d., 0.18 m film thickness

Oven: 40 C (0.7 min.), 55 C/min. to 240 C, 28 C/min. to 330 C (2 min.)

Detector: MS

Columns with small id. and thin film for FAST GC

Semivolatile analytes

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Sample introduction

(capillary column)

- Injector volume

- Injector temp. (instant

vaporization) )

- Residence time

(in split and splitless)- Deactivation of glasssurface

- Split ratio

- Solvent Effect in

splitless

COMPLETE & FAST

TRANSFER !!!!

for sharp peaks

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On-column injection

Analytes:

- Thermally labile

- Low volatility

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Wide bore col. as

Retention gap

Flooded zone formed in the retention gap

Solvent evaporating from the rear of the flooded zone

Stationary

phaseVolatile components concentrated by solvent effect

Less volatile components focused by stationary phase

A large volume injection with RETENTION GAP

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Programmed-Temperature Vaporization

(PTV)

Controlled and programmable injector temperature

cooling(cool air, liquid N2, )

heating(hot air, , ~15 oC/s)

Most solvent is removed through split valve at low temperature.

Analytes will be introduced into the column when split valve is closedand the injector is rapidly heated

injection of large sample volumes (tens - 200L )

Can be used as normal split/spitless, vapor sample introduction

Discrimination: low boiling point compounds > high boiling point compounds

(n-alkanes -> up to C16)

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Injection techniques for volatile compounds?

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Static headspace(for volatile analytes)

avoids lengthy and costly

sample preparation step !

St ti h d

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Static headspace

Phase Ratio = Vg/Vs

Partition Coefficient K = Cs/Cg

Decrease Kby

- Increasing temperature

KEtOH(air/water): 1355 (40oC) ; 328 (80oC)

- High inorganic salt concentration in aq.

phase decrease solubility organic volatileanalytes

Cg=Co/(K+)

volatile

analytes

Sample, dilution

solvent & matrix modifier

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Static headspace analysis of

saturated short chain aldehydes from cardboard(derived from lipid degradation)

1.5 g sample

MS detection

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Solid Phase Micro Extraction SPME

solventless sample preparation

For liquid and

headspace.

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Which injection modes should I select for my samples?

Split

Splitless

On-column

Purge and trap

Headspace

PTV split

Concentration

VolatilityThermal stability

Sample cleanness

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Detectors

High sensitivity

Fast response

Wide linear dynamic range

Universal/selectivity

Stability

Robustness

Ease of operation

Requirements for

ideal detectors?

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Thermal conductivity detector (TCD)

Universal (non-specific) detector Thermal conductivity of organic compounds are similar

and very different from Helium Less sensitive

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Flame Ionization Detector (FID)

Most popular

Universal

High sensitive (10-13 g C/sec)

Wide linearity range (106-107)

Robust

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Contributions of structure to the response of FID

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Electron Capture Detector (ECD)

63Ni,emitter

Gas flow

Structure selective (halogen, nitro, nitrile)

N2 N2+ +

A + A-

A- + N2+ A + N2

base current

decrease current

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Simple and reliable

Sensitive to electronegative groups (halogens, nitro, nitrile)

Largely non-destructive

Limited dynamic range (102 - 103)

ECD detector

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Relative response of the ECD to variousorganic compounds

Compounds Relative response

1-chlorobutane 1.0

1,4-dichlorobutane 15.01-bromobutane 2.8 102

1-iodobutane 9.0 104

Chloroform 6.0 104

Carbon tetrachloride 4.0 105

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MS DECTECTOR

Electron Impact Ionization (EI)

-lactam

+ M M+ + 2

A+ B+ C+

MS library(70 eV)for identification of

compounds

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MS DECTECTOR

Base peak

Molecular ion

Fragmentions

Scan mode qualitative

SIM quantitative

(selected ion monitor)

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How to analyze highly polar compounds by GC ?

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Why derivatize? Improve volatility, thermal stability, i.e. convert polar

compounds (acids, alcohols) to esters for higher volatilities sothat they can be eluted at reasonable temperatures withoutthermal decomposition or molecular re-arrangement

Enhance detector response, i.e. tagging with halogenfor ECD detection

The process of chemically modifying a compound to

produce a new compound which has properties that are

suitable for analysis using a GC

What is GC derivatization?

M i t f d i ti ti

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Main types of derivatization

Alkylation

Silylation

Acylation RCOCO-R + R'OH RCOOR' + R-CO-O-H

acid + alcohol ester + H2Oacid + alcohol ester + H2O

H+

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2,4-D in RICE MRL : 0.1mg/kg (WHO)

2,4-Dichlorophenoxyacetic acid

BP: 160 oC

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MeOH

H2SO4

Esterification (methylation)

LOD: 3 ppb

LOQ: 10 ppb

M ltidi i l GC

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Multidimensional GC

Improve separation of complex mixtures (petroleum products, PCBs,

enantiomers in flavor and food technology)

(1) acetone, (2) 2-butanone, (3) benzene, (4) isopropylmethylketone, (5) isopropanol, (6) ethanol,

(7) toluene, (8) propionitrile, (9) acetonitrile, (10) isobutanol, (11) 1-propanol, (12) butanol

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Heartcut GC x GC

A

C1: Poly(ethyleneglycol)

BCut

C2: Poly(dimethylsilosane)

C5 C6 C7

(1) acetone, (2) 2-butanone, (3) benzene, (4) isopropylmethylketone, (5) isopropanol, (6) ethanol,

(7) toluene, (8) propionitrile, (9) acetonitrile, (10) isobutanol, (11) 1-propanol, (12) butanol

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Comprehensive two-dimensional GC

TOTAL TRANSFER of all sample components from the first column to the

second column as a series of pulses which are separated sequentially and

individually on the second column 1D long (conventional) column

2D short column (for very fast separation, few seconds / run)

Cryogenic trap

to refocus heart-cuts

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2D GC separation

1D separation

2D separation

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Illustration of how two overlapping peaks emerging from D1 (A) are

resolved in GC x GC after passage to D2 (B).

Sources of activity of glass surface

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Metal ions, boron

Silanol groups

Si OH

Si OH

> 3.1m

Strong

Free silanol Geminal silanol

SiOH

OH

Weak or none

Weak or none

Si O H

Si O H

Vicinal silanol

Si O H

Si O HO

H

H

Strong

Hydrated silanol