1. The Foundations: Classical Split and Splitless Injection
Nicholas H. Snow
Department of Chemistry
Seton Hall University
South Orange, NJ

2. Split and Splitless Split Splitless Both use the same hardware
vaporize and remove most of the sample to waste
Splitless
vaporize and transfer most of the sample to the column; use cold trapping and solvent effects to focus bands
Both use the same hardware

3. Split Inlet Use for higher concentration samples ppm and above
hot inlet; vaporize sample
mix with carrier gas
use purge valve to “split” the sample
split ratio is critical
place fraction of sample on column

4. SPLIT INJECTION High Temperature High Linear Velocity Rapid Transfer
Bulk of Sample Wasted
Split Ratio Important
Liner Geometry

5. Classical Split Ratio Determination
Measure column flow from tm
Fc = pr2L/tm
Measure purge vent flow using flow meter Fs
Split Ratio = Fs / Fc
What are the problems with these measurements?
Do we really ever know how much we injected?
Does the exact injection volume matter?

6. Modern Split Ratio Determination
EPC systems measure pressures and flows directly
Column flow is calculated from inlet conditions and column dimensions
add equation here
Purge flow adjusted to desired value

7. Flow Equations

8. Advantages of Split Inlets
Reduced sample size (narrow bands)
Fast inlet flow rate (narrow bands)
Dirty samples OK
Simple to operate (best for isothermal GC)
Inject “neat” samples
Excellent interfacing

9. Disadvantages of Split Inlets
Nonlinear splitting
high molecular weights can be lost preferentially
Thermal degradation
hot metal surfaces can lead to reaction
Syringe needle discrimination
Trace analysis limited
ppm detection limits with FID

10. Split Injection Techniques
Filled Needle
Cold Needle
Hot Needle
Solvent Flush

11. Split Inlet Discrimination

12. Summary - Split Inlet Simple Hot vaporizing technique
syringe discrimination (best to use autosampler)
liner discrimination
use glass wool (deactivated)
shape of liner may be critical
Best for “neat” or concentrated samples
high ppm or higher

13. Splitless Inlet Inject sample into hot inlet without “purge”
95% of sample enters column
Same hardware as split except liner
More variables
solvent, splitless time, initial column temperature
Open purge valve after short time
Better sensitivity

14. SPLITLESS INJECTION High Temperature Low Liner Velocity Slow Transfer
Bulk of Sample and Solvent to Column
Many Factors Important

15. Steps in a Splitless Injection
Purge valve is off; column is cold
Inject sample
fast autosampler injection best
slower injections have been proposed
Flow through inlet is slow; slow transfer to cold column
After sec, open purge valve - cleans inlet
Temperature program column

16. BAND BROADENING Time Space (solvent effect) Thermal Focusing Time
Grob, K., Split and Splitless Injection in Capillary GC, Huthig, 1993, pp ,

17. Band Focusing Mechanisms
Splitless injections involve slow transfer to column ---> initial peaks are broad
Need focusing
cold trap
solvent effects

18. Cold Trap
Initial column temperature cold enough to “freeze” analyte on column

19. INITIAL COLUMN TEMPERATURE
20oC
0oC
40oC
hexane, heptane
500 ppb
10 min extraction
Fiber: PDMS 100 m
LinermmoC
Pinj: 1 bar(g)
-20oC
-40oC

20. Solvent Effects Solvent is recondensed in the column
Long plug of liquid
Start column degrees below normal boiling point of solvent

21. Solvent Effects

22. Solvent Effects Refocus moderate volatility compounds near column head
Require solvent to wet stationary phase
Use non-polar solvent with non-polar stationary phase, etc.

23. INITIAL COLUMN TMPERATURE SOLVENT EFFECT INJECTIONS
40oC
60oC 20 20
Time (min)
Time (min)
Solvent: Cyclohexane (bp 81oC), Sample: 10ppm hydrocarbons

24. INLET TEMPERATURE REALITY
Set Point 350oC
Distance
from
Septum
(mm)
Carrier Gas Temperature (oC)
Klee, M.S., GC Inlets: An Introduction, Hewlett Packard, 1991, p. 42.

25. INLET TEMPERATURE CHROMATOGRAMS2
70000
250oC 3 4 5
1. octane
2. decane
3. tridecane
4. tetradecane
5. pentadecane HP
Pinj = 5.0 psi
HP5 30m x 0.25mm
x 0.25 mm
Transfer: 280oC 1
100oC
40000
TP: 40oC initial, 1 min, 10oC/min

26. INLET PRESSURE Linear Gas Velocity Increased Injector Column
Analyte Boiling Point Increased

27. PRESSURE PULSE Increased Pressure During Injection Only Time (min)
Purge “ON” Time
150
Pressure
(kPa) 50
0.75 20
Time (min)

28. PRESSURE PULSE 20000 5 1. octane 2. decane 3. tridecane 4. tetradecane
5. pentadecane HP
Pinj = 5.0 psi
HP5 30m x 0.25mm
x 0.25 mm
Transfer: 280oC
No Pulse 4 3 2 1
40000
10 psi pulse
Pressure increased to 15 psig during splitless period
TP: 80oC initial, 1 min, 10oC/min

29. OPTIMIZATION SPLITLESS INJECTION
Can Be Difficult
Minimize Transport Time (high linear velocity)
Maximize Thermal Focusing (low initial column temperature)
Maximize “solvent effect” (low initial column temperature)
Chemistry remains a factor

30. REFERENCES
Grob, K. Split and Splitless Injection in Capillary GC, 3rd. Edition, A. Huethig, 1993.
Klee, M.S., GC Inlets: An Introduction, Hewlett Packard, 1991.
Stafford, S.S., Electronic Pressure Control in Gas Chromatography, Hewlett Packard, 1993.