Carrier Gas and EPC 2009-print version.ppt...EPC CAUTIONS Things to be aware of Carrier Gas...

1

Carrier Gas Selection

Carrier Gas Considerations and Utilizing the EPC


Page 2

Column

FlowController

Regulators

Air

Hyd

rog

en

Ca

rrie

r G

as

Mol-SieveTraps

Fixed

InjectionPort Detector Electrometer

Recorder/Integrator

Restrictors

Cylinders or Generators

Typical Gas Chromatographic System

Selection of type and velocity

influences efficiency and retention time

2


Carrier Gas

Affects resolution and retention time

Optimal range of velocities

Too low or high results in loss of resolution


Page 4

A = Multi-path termB = Longitudinal diffusion termC = Mass transfer term

uh = A + B + Cu

h = Height equivalent to a theoretical plate

uh = B + Cu

Packed Columns

Open-Tubular Columns

van Deemter Equation

3

HE

TP

HETPmin

Uopt u

HETP

uA + C

B/u A

HE

TP

HETPmin

Uopt u

HETP

uCB/u

Packed ColumnsHETP = A + B/u + Cu

Open-Tubular ColumnHETP = B/u + Cu

van Deemter Curves



Page 6

van Deemter Curve

10 20 30 40 50 60

0.25

0.50

0.75

1.00

u (cm/sec)

h

ūoptOPGV

Excessive Diffusion

Poor Mass Transfer

4


Page 7

uopt and OPGV

uopt: Optimum gas velocity (slowest velocity!)

Maximum efficiency

OPGV: Optimum practical gas velocity Maximum efficiency per unit time

(1.5 to 2) X uopt

Best u = Balance resolution and analysis time


Page 8

Nitrogen = 0.15 cm2/sec

Helium = 0.4 cm2/sec

Hydrogen = 0.6 cm2/sec

© Walter Jennings, 1999

Diffusion Constants for Dodecane @ 150oc

5


Page 9

10 20 30 40 50 60

0.25

0.50

0.75

1.00

u (cm/sec)

h

12-20 cm/sec

N 2

van Deemter CurveNitrogen


Page 10

10 20 30 40 50 60

0.25

0.50

0.75

1.00

u (cm/sec)

h

He

28-40cm/sec

van Deemter Curve Helium

6


Page 11

10 20 30 40 50 60

0.25

0.50

0.75

1.00

u (cm/sec)

h H2

38-60 cm/sec

van Deemter Curve Hydrogen


Page 12

Carrier Gas - Hydrogen Comments

Hydrogen is extremely diffusive in air

Difficult to reach explosive level of ~4 %

Most GC's flow regulated with safety shutdown

Spring loaded/Explosion ready doors

7

Hydrogen as Carrier – Contamination?


Page 13

Contamination of GC flow modules and lines.

Hydrogen acts as a scrubber.

On the MS this typically looks like Hydrocarbon contamination

Most people report that it takes 2-4 weeks to clean out, depending on flows.

The FID only sees a high background for that time.

Hydrogen seems to scrub the lines of that which Helium leaves behind.

Page 14

Contamination?! – scrubbing or vapor volume


8


Page 15

Hydrogen as Carrier – MS and Lower Pressures

Hydrogen is more difficult for the MS vacuum system to pump away as compared to Helium.

Be careful not to get to a “negative” head pressure situation. (pulling instead of pushing flow is not good).

Trace level work on the MS requires low flow rates.

Must use smaller ID columns so you don’t have higher flow rates. (length plays a role as well)

0.18mm ID or smaller is ideal for trace level MS work when using Hydrogen.

Page 16

Fast DHA Analysis – 33% Faster with Hydrogen

min0 50 100

min.0 50 100

100 m x 0.25 mm, 0.5µm HP-1helium

100 m x 0.25 mm, 0.5µm HP-1hydrogen


9

Page 17

Fast DHA Analysis – Resolution Check

min.0 50 100

100 m x 0.25 mm, 0.5µm HP-1helium

0 50 100

100 m x 0.25 mm, 0.5µm HP-1hydrogen


Page 18

10.0

11.0

12.0

13.0

14.0

15.0

16.0

17.0

18.0

19.0

20.0

21.0

22.0

23.0

24.0

25.0

26.0

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0

1

2

3

4 5

6

7

8

910 11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28a

28b

28c

29a 29b

29C

30

Helium as Carrier Gas

InjectorTemperature 225 CPressure 16.2 psiSplit Ratio 25Split Flow 37Total Flow 42.2Flow 1.5 mL/minMode Constant Flow

OvenC/min Temp. (C) Time (min.)

40 3.8413.01 200 1.87

DetectorFIDHydrogen Flow40 mL/minAir Flow 400 mL/minMkup 20 mL/min

1. Methanol2. Pentane3. Ethanol4. Diethylether5. Acetone6. Isopropanol7. Acetonitrile8. Methylenechloride9. t-Butanol10. Methyltertbutylether11. Hexane12. n-Propylalcohol13. Ethylacetate14. Tetrahydrofuran15. Cyclohexane16. Isobutylalcohol17. Isopropylacetate18. Heptane19. n-Butanol20. Methylcyclohexane21. 1,4-Dioxane22. Methylisobutylketone23. Toluene24. Isobutylacetate25. Ethyleneglycol26. n-Butylacetate27. Dimethylformamide28a,b,c. Xylenes29a,b,c. Dimethylacetamide30. N-Methylpyrilidone

DB-624 30m x 0.25mm x 1.4µmSolvents in Drugs


10

Page 19

Solvents in Drugs


Page 20

20.0

21.0

22.0

23.0

24.0

25.0

26.0

27.0

28.0

29.0

30.0

31.0

32.0

33.0

34.0

35.0

36.0

0.0

10.0

11.0

12.0

13.0

14.0

15.0

16.0

17.0

18.0

19.0

20.0

21.0

22.0

23.0

24.0

25.0

26.0

0.0

1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0

Helium to Hydrogen saves an additional 5 minutes (33%)


11

Faster GC Analyses

Page 21

20.0

21.0

22.0

23.0

24.0

25.0

26.0

27.0

28.0

29.0

30.0

31.0

32.0

33.0

34.0

35.0

36.0

0.0

10.0

11.0

12.0

13.0

14.0

15.0

16.0

17.0

18.0

19.0

20.0

21.0

22.0

23.0

24.0

25.0

26.0

0.0

10 min

15 min

Resolution Check

Volatile Chlorinated Solvents on a Megabore


12

Min

ute

s

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

Volt

0.0

0

0.0

1

0.0

2

0.0

3

0.0

4

0.0

5

0.0

6

0.0

7

0.0

8

0.0

9

Volt

0.0

0

0.0

1

0.0

2

0.0

3

0.0

4

0.0

5

0.0

6

0.0

7

0.0

8

0.0

9

Methyl Chloride 59172

Vinyl Chloride 85885

Vinylidene Chloride 88170

Methylene Chloride 35179

trans 1,2-Dichloroethylene 76057

A-Di 85299

cis 1,2-Dichloroethylene 77970

Chloroform 32298

Carbon Tetrachloride 29443

Ethylene Dichloride 74714

Trichloroethylene 70046

1,1,2-Trichloroethane (B-tri) 51838

Perchloroethylene (1,1,2,2) 53142

Tetrachloroethylene 47308

Are

a

Min

ute

s

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10

.0

Volt

0.0

0

0.0

1

0.0

2

0.0

3

0.0

4

0.0

5

0.0

6

Volt

0.0

0

0.0

1

0.0

2

0.0

3

0.0

4

0.0

5

0.0

6

Methyl Chloride 60921Vinyl Chloride 84781

Vinylidene Chloride 85285

Methylene Chloride 36048

trans 1,2-Dichloroethylene 77501

A-Di 86539

cis 1,2-Dichloroethylene 80678

Chloroform 27134

Carbon Tetrachloride 20238

Ethylene Dichloride 78755

Trichlorethylene 74357

1,1,2-Trichloroethane (B-tri) 61556

Perchloroethylene (1,1,2,2) 60576

Tetrachloroethylene 52461

He

lium

Ca

rrier/H

eliu

m M

ake

-up

Hyd

roge

n C

arrie

r/Nitro

ge

n M

ake

-up

Carrie

r Gas S

ele

ctio

n

Page 2

4

Meg

ab

ore

with

Hyd

rog

en

Carrie

r -

co

uld

giv

e a

baselin

e ris

e a

s th

e to

tal H

2 in

cre

ases

150C

Carrie

r Gas S

ele

ctio

n

13

Page 25

Isothermal column bleed and Hydrogen increase


Page 26

Temperature program column bleed with increasing Hydrogen


14

Oth

er C

hlo

rinate

d S

olv

en

ts o

n a

Meg

ab

ore

Carrie

r Gas S

ele

ctio

n

23

45

67

89

10

0 20 40

D M E M e t h y l C h lo r id eV in y l C h lo r id eM e t h a n o l

E t h y l C h lo r id e

V in y l id e n e C h lo r id e

M e t h y le n e C h lo r id e

T ra n s

A -d i

C is

M 3a -T r i

M 4E D C

T c eP D C

(U n n a m e d P e a k s )

B -T r iP C E

M C B (M o n o c h lo ro b e n z e n e )1 , 1 , 1 , 2 - U n s y m . T e t ra s

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56

78

910

1112

2 . 2 0 02 . 2 7 02 . 6 5 02 . 7 1 72 . 8 6 7

3 . 1 2 3

4 . 4 8 74 . 6 0 34 . 9 7 0

5 . 1 3 35 . 5 2 7

6 . 1 0 3

6 . 9 0 7 7 . 3 3 0

7 . 6 1 77 . 8 5 7

8 . 1 3 7

9 . 0 0 39 . 3 0 0

1 0 . 9 3 31 1 . 0 9 71 1 . 1 7 7

1 1 . 9 0 31 1 . 9 6 71 1 . 9 9 31 1 . 9 9 3H

eliu

m 1

0 m

L/m

in

Hyd

roge

n 1

2.5

mL

/min

Carrie

r Gas S

ele

ctio

n

15

Page 29

DB-1, 60m x 0.32mm x 0.25um

Helium

Fast Analysis/Hydrogen

Translate to Hydrogen

Steam Cracked Naphtha


Page 30

Steam Cracked Naphtha


16


Page 31

10 20 30 40 50 60

0.25

0.50

0.75

1.00

u (cm/sec)

h

He

N2

H2

van Deemter Curves


Carrier Gas Comparison

Hydrogen is difficult to explode under GC conditions

Gas Advantages Disadvantages

Nitrogen Cheap, Readily available Long run times

Helium Good compromise, Safe Expensive

Hydrogen Shorter run times, Cheap Explosive

17


Page 33

Carrier Gas - Selection Summary

Hydrogen is best especially for wide k range analyses

Helium is acceptable

Nitrogen is not recommended


Page 34

Carrier GasProperties

Expands to fill the space it occupies

Expands with increase in temperature

Viscosity increases with temperature

Compressible

THEREFORE:Flow increases as it goes down the length of the column

AND At Constant Pressure:

T u

18

Page 35

EPC To The Rescue!


Page 36

BENEFITS OF EPC

Reliability and Reproducibility of set-points

(ambient temperature and pressure compensation)

Choice of constant flow versus constant pressure

Ability to Pulse flow during injection to buffer expansion and increase speed of transfer and amount on column

Flow ramping available to reduce time at the end of the analysis or during Bake Out


19

Page 37

EPC CAUTIONSThings to be aware of

EPC doesn’t measure flow or velocity, they are calculated, THEREFORE…

Dimensions of the column, length and especially internal diameter, must be entered precisely or an errant velocity will result.


Page 38

F =16 η L

(pi2 - po

2)

po

π r 4

Volumetric flow is a quadratic to the fourth power function of radius

Linear velocity is a squared function of radius

Length has less of an impact

The Poiseuille Equation

Affects Of Column Radius And Length


20

Page 39

Pulsed Splitless- sample containment more critical than in split injection- much sharper peaks than in traditional splitless injection

Pulsed Split- the most volatile components and solvent effected most- faster sample transfer not as critical since it’s already fast

EPC for Split/Splitless Pulsed Injection

Pressure Pulse contains sample expansion and transfers analytes to the column faster.


Page 40

Splitless Injection

Column Flow1 mL/min

(Septum) PurgeVent Flow3 mL/min

Sample Injection

Split Vent Flow0 mL/min

Total Flow4 mL/min

Syringe Needle

Sample


21

Page 41

Splitless Injection

Injection Overload = Backflash

Column Flow1 mL/min

Split Vent Flow

(Septum) Purge

Column Flow1 mL/min

Split Vent Flow

(Septum) PurgeVent Flow

3 mL/minTotal Flow

1 mL/min

Split Vent Flow

0 mL/min

(Septum) PurgeVent Flow

3 mL/minTotal Flow

4 mL/min

= Solvent Vapor

= Analyte Vapor


Page 42

10

20

30

40

50

60

70

80

90

50 100 150 200 250 300 350 400

Injection Port

Set Point Temperature

350°C

35°C

Oven150°C

Oven300°C

Oven

Temperature in Gas Stream (°C)

Bottom

of Septum

Syringe

Tip

Base of

Injection

Port

Temperature Profile of a Typical Vaporization Injector vs Oven Temperature


22

Page 43

Solvent Expansion Equation

Solvent Vapor Volume = 22,400 x A x B x C x I

A = solvent density/solvent molecular weight

B = 15/(15 + column headpressure [in psi])

C = (Injection Port Temperature[°C] + 273)/273

I = liquid injection volume [µL]

Example

1 µL of water injected at 250 °C under 15 psi headpressure

22,400 x 1/18 x 15/30 x 523/273 x 1 = 1,192 µL vapor


Page 44

Pressure Flow Calculator &

Solvent Vapor Volume Calculator


23

Page 45

Pressure Flow Calculator


Page 46

Solvent Vapor Volume Calculator


24

Minimizing Backflash

Large volume liner

Small injection volume

Low expansion solvent

Low injector temperature

High carrier gas flow rates (EPC?)

High head pressures (EPC?)


Page 48

Benefits of the Pulsed Splitless Mode

20

30

40

50

60

70

80

90

100

110

120

70 psi

pulsed splitlesson column

22.5psi

pulsed splitless

Injection Type

% R

eco

very

(o

n c

olu

mn

=100)

Methamidophos

Acephate

Azobenzene

Omethoate

Diazinon

Dimethoate

Chlorpyrifos

High Column Flow

Normal Column Flow

% Recovery of Each Labile Pesticide Relative to Cool On-Column injection


25

Select Pulsed Splitless Mode in Inlets


Page 49

Check the Splitless Pressure


Page 50

26

Double or Triple the Pressure for ~1 sec less than the Purge Activation Time


Page 51

Page 52

Flow Ramping for Late Eluter with EPC

6.00 8.00 10.00 12.00 14.00 16.00

GC3-6707.D\ECD2B

With Flow Ramp

No Flow Ramp


27

Page 53

EPC Flow Ramping forLate Eluters and Faster Bake Outs


Using Method Translator for Calculating Pressure Needed for a Given Flow at a Given Temperature


Page 54

28

Using Chemstation for Calculating Pressure Needed for a Given Flow at a Given Temperature


Page 55

Conclusions


Page 56

Carrier Gases have an optimum range of velocities -Too low or high results in loss of resolution

Hydrogen is the best carrier gas for high velocity work -Can be used safely in 6890/7890-Lighter molecule that Helium-Lower pressure considerations

EPC gives the ability to change flow reproducibly -Pulsed Injection (efficiency, backflash)-Flow Programming (bake out, late eluters)

Carrier Gas and EPC 2009-print version.ppt...EPC CAUTIONS Things to be aware of Carrier Gas...

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Transcript of Carrier Gas and EPC 2009-print version.ppt...EPC CAUTIONS Things to be aware of Carrier Gas...