Chapter 7Gas Chromatograph

7.1 Introduction to Interphase Separations1. Interphase Separations

Mixed Substances

Mobile Phase

Stationary Phase

Separated

Components

2. Classification of ChromatographyInstrumentation

• By the types of mobile phase & stationary phase

Gas - Liquid GLC

Gas - Solid GSC

Liquid - Liquid LLC

Liquid - Solid LSC

• By stationary’s formsColumn

Paperthin layer

• By separation mechanism

absorption

partition

exchange

3. Typical GCS Progresses

Carrier gas

Column

InjectorSample

Detector

Chromatogram

7.2 Principle of GC

1. The Interphase Partition of One Substance

C(m) C(s)

(1) Partition Coefficient K

m

s

C

CK 7-1

(2) Partition Ratio k

p, q : mass fraction in the stationary and mobile phase

k: Partition Ratio or Capacity factor

m

s

q

pk

1 ms

m

ms

s

www

wwwqp

kV

V

q

p

Vq

Vp

C

CK

s

m

m

s

m

s /

/

: phase ratio

7-2

7-3

7-4

2.Theoretical Plate

(1) Some common relationship

qkqppq

q

Vc

cV

Ft

tF

F

F

uA

Au

u

uR mmmmm

s

1

1

/1

1

(2) Theoretical Plate Model:•Height Equivalent to a Theoretical Plate(HETP)

•Gas Flow rate is 1 plate Volume per time

•K is a constant

•Sample come into the plate only by the plate No. 0

7-5

Binomial distributing

rrnr

nrn

n

rrn

n

qpcf

fqp

,

1,

7-7

7-6

rnsrn

rnmrn

pfW

qfW

,,

,,

3. Export Curve Equation

(1) Export Curve Equation (Gauss distribution)

eRttc

c 2

2

20

2

7-8

(2) The Shape of Export curve

tm (tair): unreteined time

tR: retention time

T’R: adjusted retention time

Vm (Vair): unreteined volume

VR: retention volume

V’R: adjusted retention volume

h: Peak of zone : Standard deviation

Y: Width of zone Y1/2: Half peak width

mRR ttt '

36.22ln222/1 Y4 Y

m

R

t

tk

'

)1( ktt mR

7-97-10

7-11

7-12

7-13

(3) The Number of theoretical plate and HETP22

2/1

1654.5

Y

t

Y

tn RR

22

2/1

'16

'54.5

Y

t

Y

tn RR

effect

effecteffect n

LH

effectnk

kn

1

L: length of the column

7-14

7-15

7-15

7-17

4.Van Deemter Equation

u: velocity of the carrier gas

A, B and C are the constants for a given system

cuu

BAH 7-18

7.3 Separation of Components

1. Separation for tow components(1)Resolution R

)21

1,2,

(5.0 YY

ttR RR

(2)Separation Factor

1

2

1

2

1

2

1

2

'

'

'

'

V

V

t

t

k

k

K

K

7-19

7-20

2. Separation Equation of GC

Assume: Y1=Y2=Y, k1≈k2=k

212

1216 k

kRn

2

1216

Rneffect

1

41 effectnR

7-21

7-22

7-23

3. Three Separation factor

(1) Column effect factor n

(2) Capacity factor k

(3) Selective factor

4. The Choice of experimental qualification

(1) Flow rate of carrier gas

cuu

BAH

uu

B

du

dH

2

CB

bestu

BCAH 2min

7-24

7-25

7-26

7-27

(2) Column temperature

low mid high

100～ 200℃ 200 ～ 300 ℃

300 ～ 400 ℃

(3) Column types • Stationary type

• Stationary Liquid and Temperature

• Supporter

(4) Injection time and volume

7.4 GC Instrument

1. Gas Supply

Type Function

Hydrogen Carrier, Fuel gas

Nitrogen Carrier

Helium Carrier

Argon Carrier

2. Sample Injector

3. Column System

(1)Capillary GC Columns

(2) stationary phases

Polysiloxanes

4. Detector(1) Two Kinds of Detectors

Thermal conductivity detector (TCD)

While equilibrium: R1R3=R2R4

Electron capture detector (ECD)

Flame ionization detector (FID)

Flame photometric detector (FPD)

(2) Behavior of Detector

• Sensitivity

CSR c

a) for concentration typesQ

RS

0

Am

FkSc

7-28

7-29

7-30

b) For mass types

dt

dmSR m

Am

kSm

1

•Detect limit

S

ND

2

N: noise of detector(mV) A: area of the signal

7-31

7-32

7-33

• Minimum detect quantity Q0

•Response time

•Linear response range

DYA 2/1065.1For mass:

For concentration:

DYQ 2/10 065.1

FDYQ 2/10 065.1

7-34

7-35

7-36

7.5 Qualitative analysis

1. Comparison with pure maters

2. Work as a part of analysis system

GC-IR GC-MS

3. Retention Index

7.6 Quantitative analysis1. Quantitative Equation For same detector, different substance have

different response sensitivity.

iii Afm Is called as Quantitative correction factorif

The equation Is Quantitative Equation.

jjj

iA

jj

i

T

ii Af

f

m

m

m

mm i%

7-37

7-38

2. Determination of zone area

(1) By calculation

2/1hYA

2/1065.1 hYA

hYA

RhtA

(2) Numerical integral by computer

(3) By instrumental integral

3. Normalization Methods Assume the zones of every substance mj

in sample have obtained, so:

%100

%100 %100%

jjj

ii

jj

i

T

ii

fA

fA

m

m

m

mC

%100% i

iC

7-39

4. Internal standard MethodsUse a internal standard sample its mass is a constant known as ms and its zone area is As

sss

iii m

Af

Afm

s

i

s

i

s

si

s

ss

iiii

A

AK

A

A

mf

mf

m

m

Af

Af

m

mC

%100

%100%100%

7-40

7-41