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statIc headspace
Static Headspace is a technique used for sampling the gas phase of a sample. The technique can be used for
both qualitative and quantitative analysis. Static Headspace can be separated into three basic operations, Sample
Equilibration, Sampling and Injection. In this section of the manual the basics of Static Headspace will be described.
sample equilibration
The analysis is completed in a closed system making it impossible for the system to create or lose mass. When a
sample reaches equilibrium, the mass in the matrix plus the mass in the gas must equal the original mass placed in the
vial. (Refer to Equation Below)
mass balance equation
M
O
= M
G
+ M
M
M
O
= Original Mass Placed in the Vial
M
G
= Mass in the Gas Phase After Equilibrium
M
M
= Mass in the Matrix After Equilibrium
The amount of mass that leaves the matrix for the gas phase is dictated by the partition coefficient (K). This is a
physical constant that is directly affected by the temperature of the sample and the pressure in the vial. Assuming
that the make-up of the matrix and the volume is consistent, the pressure in the vial can be disregarded since each
vial should create approximately the same internal pressure after heating; this is called the Static Vial Pressure. If
this does not hold true for a particular set of samples, refer the Method Development Section of this manual for
further instruction. If the sample temperature is held constant for the appropriate amount of time, the system will
reach equilibrium.
Introduction • Page 1-4
Figure 1-1: Headspace Equilibrium Diagram
Introduction