Impact Of K And Phase Ratio - Agilent Technologies 7697A Advanced Operation Manual

3
Method Development

Impact of K and phase ratio

30
Rearranging provides:
C
O
C =
G
V
G
K +
V
L
where:
K is the partition coefficient (or distribution coefficient),
C /C at equilibrium
L G
V /V is also called the phase ratio
G L
The equation shows two important points:
• For consistent results, the ratio V
constant. This means that the sample amount and vial
size need to be kept the same.
• Minimizing the partition coefficient, K, provides higher
concentration of sample vapor in the headspace volume.
• A smaller V /V ratio yields a greater concentration of
G L
volatile of interest in the headspace volume
The concentration of analyte in the headspace volume
depends on many factors, including: sample amount, original
concentration of analyte in the sample, available headspace
volume, temperature, and total pressure in the vial. Some
factors are manipulated in the sample and in the matrix,
while others can be controlled using the headspace sampler.
/V must remain
G L
Advanced Operation