Thermo Scientific TriPlus RSH, Руководство пользователя

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1
Getting Familiar with Your TriPlus RSH
MHE Station
Thermo Scientific TriPlus RSH User Guide 53
However, A(0) = ½ * A(ref ) and thus:
A(tot) = ½ * A(ref ) * 2/a, or
A(tot) = A(ref )/a
If
α
=1 (the entire headspace is exchanged between each extraction) then:
A(tot) = A(ref )
If
α
= ½ (half of the headspace is exchanged between each extraction step) then:
A(tot) = 2 * A(ref )
In this case A(tot) will be over-determined by a factor of two relative to A(ref ). In other words,
the content of analyte will be over-determined by a factor of two.
Situation 4
Similar to Situations 1 to 3 as described above, the general description for an equilibrium
distribution with
β
being the relative amount of the analyte in the gas phase (in the
headspace) and ? being the relative amount of the headspace that is exchanged between each
successive extraction, is given by:
A(tot) =
β
* A(ref ) * (1 + (1-
α
*
β
) + (1-
α
*
β
)2 + …)
Using the expression for the geometric sum yields:
A(tot) =
β
* A(ref )/(1-(1-
α
*
β
)) =
β
* A(ref ) * 1/(
α
*
β
)
or:
A(tot) = A(ref )/
α
That is: the total area, A(tot), will be over-determined by a factor of 1/
α
relative to A(ref ).
In other words, the content of analyte will be over-determined by the factor 1/
α
. Thus the
total area will depend on the amount of headspace removed during each successive extraction,
but it will not depend on the position of the equilibrium (
β
).
Conclusion
If the headspace is only partially removed/exchanged between each extraction, the total area
that results from the MHE determination will be greater than A(ref ), where A(ref ) denotes
the area from a pure gas standard measured only once).
Therefore, if MHE quantification is performed based on a singly-determined gas standard,
the amount of analyte in the sample will be overestimated by a factor of 1/?, with ? being the
amount of the headspace that is removed/exchanged between each successive extraction.