This document discusses key terminology and parameters used in headspace gas chromatography (HSGC). It explains the differences between a loop-pressure system and a pressure balanced system. Key terms defined include oven temperature, needle temperature, transfer line temperature, thermostatting time, pressurization time, injection time, withdrawal time, GC cycle time, and vial venting time. The document also covers loop fill time, loop equilibration time, inject time, and multiple headspace extraction.

1. Understanding of
Gas chromatography
Headspace parameters
Ankur Gupta
(Ph.D. Chemistry)

2. Terminology used for HSGC
Headspace sampler Loop-pressure system Pressure Balanced system
(Agilent) (Perkin Elmer)
Temperature Oven Oven
Temperature Loop Needle
Temperature Transfer line Transfer line
Time GC Cycle GC Cycle
Time Sample Eq. Thermostating
Time Pressurize Pressurize
Time Loop fill Not applicable
Time Loop Equilibrium Not applicable
Time Injection Injection
Vial pressure Psi Psi
Shaking Low/High On/off
loop volume 1ml/3ml Not applicable

3. Pressure Balanced system
(Perkin Elmer)

4. Loop-pressure system
(Agilent)

5. Oven (Vial) temperature:
The temperature at which
sample is equilibrate in
HS vial.
It is set so that the
maximum amount of
analyte is moved into the
headspace in the
minimum time without
(or minimum) disturbing
the sample thermal
stability.

6. Needle/Loop temperature:
 The needle/loop is
heated so that the
sample vapors does not
condense in the needle
during injection.
 For best reproducibility,
set the needle/loop
temperatures to a value
5-10 ºC higher than the
oven temperature.

7. Transfer Line Temperature:
 The transfer line is
heated so that the
sample vapors does
not condense in the
transfer line during
injection.
 For best reproducibility,
set the transfer line
temperatures to a
value 5-10 ºC higher
than the needle/loop
temperature.

8. Thermostatting/vial equilibration
time:
 The thermostatting
(vial) equilibration
time is the time
required to
thermostat the vial
in HS oven.

9. Pressurization time:
 After equilibrium
has been reached,
the vial is
pressurized by the
carrier gas to a
pressure equal to
the sampling head
pressure (P2).

10. Injection time:
 After pressurizing vial,
the carrier gas supply
is interrupted by
closing a valve in the
carrier gas supply line
and the pressurized
gas in the vial expands
onto the column,
resulting in a flow of
the headspace gas
from the vial to the
column.

11. Withdrawal Time:
 The length of time
after the injection,
before the sample
needle is withdrawn
from the sample vial
or lowered into the
vent position. During
this time the needle
remains in the vial.

12. GC Cycle Time:
 The GC cycle time is the minimum time
between a sample injection and the time
at which the GC is ready for the next
injection. This time will be determined
from the GC analysis time and the time
required to return the GC to its ready
state.

13. Vial Venting:
 This will be the
length of time
during which the
vial is vented to
atmosphere.

14. Column Pressure:
 This is the carrier gas pressure for the HS
system. The carrier gas is used to
pressurize the vials and then carry the
sample through the transfer line to the GC
injector or column.

15. Loop Fill Time:
 Time in which the headspace/vial
pressurization gas mixture passes through
the sample loop to vent. This fills the
sample loop with a precise amount of
headspace gas.

16. loop equilibration time:
 Time after the vent valve closes to allow
the analytes in the sample loop to
equilibrate to the higher loop temperature
and to allow pressure and flow in the loop
to stabilize.

17. Inject Time:
 Time in which the gases in the sample
loop are injected into the GC. The actual
time needed depends on the carrier flow
rate and the sample loop size.

18. Multiple Headspace Extraction
(MHE)
 MHE is used to sample the same vial
repeatedly. The vial is raised on to the
sampling probe, sampled, and lowered off
of the probe for each extraction.

19. Pressure
Balanced system
Loop-pressure
system
Standby
Standby

20. Pressure
Balanced system
Loop-pressure
system
Pressurization
Pressurization

21. Pressure
Balanced system
Loop-pressure
system
Loop filling
Not
applicable

22. Pressure
Balanced system
Loop-pressure
system
Not
applicable
Loop equilibrium

23. Pressure
Balanced system
Loop-pressure
system
Sampling

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