Consider The Sample And Matrix; Theory Of Headspace Analysis - Agilent Technologies 7697A Advanced Operation Manual

Consider the Sample and Matrix

Theory of headspace analysis

Advanced Operation
The first step in developing the method is to understand the
sample and matrix.
The equations describing headspace theory derive from three
physical laws associated with vapor pressure, partial
pressures, and the relationship between vapor pressure of an
analyte above a solution and the concentration of that
analyte in the solution.
Dalton's law of partial pressures states that the total
pressure of a mixture of ideas gases is equal to the sum of
the partial pressures of each gas in the mixture.
Henry's law for dilute solutions states that at a constant
temperature, the amount of a given gas dissolved in a given
type and volume of fluid is directly proportional to the
partial pressure of that gas in equilibrium with that fluid.
Raoult's law states that the partial pressure of a solute in
the headspace volume is proportional to the mole fraction of
the solute in solution.
The concentration of sample analyte in the headspace
volume is given by mass balance:
C V = C V + C V
O L G G L
where:
C is the concentration of analyte in the headspace
G
C is the concentration of analyte in the original sample
O
V is the volume of gas in the sample vial
G
V is the volume of sample
L
K is the partition coefficient (or distribution coefficient),
C /C at equilibrium V
L G
Method Development
L
/V
G L
3
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