70
known analytical standards. Ethylene has a much lower solubility than C 2 H 2 and the
bulk of that produced migrated back to the gas phase.
Ethylene production rates are calculated according to the equation:
Peak Ht C H
Peak Ht C H
Std nmol ml GPV SC nmol C H
samp
std
2 4
2 4
2 4
*[
] *
*
=
/
(5.1)
“Area of the peak” may be substituted for the sample and standard response for
the peak height on the gas chromatograph. “GPV” represents the gas phase volume
in ml. “SC” is the solubility correction which accounts for ethylene remaining in
solution and is calculated as:
SC
A B
= + *
(
)
1 a
/
(5.2)
Where “α” represents the Bunsen solubility coefficient, “A” is the volume of the
aqueous phase and “B”, the volume of the gas phase (= GPV).
To derive a rate from endpoint assays:
nmol C H
nmol C H
T T
nmol C H formed per t
tn
t
n
2 4
2 4
0
0
2 4
@
@
-
-
=
(5.3)
Where T 0 is the start point of the assay when C 2 H 2 is added and T n is at a time
point after a period of incubation, typically minutes to hours depending on the system being assayed.
Experiments can also be conducted over time courses and the rate of C 2 H 4 production derived by linear regression analysis from the initial linear rates. Samples
are typically normalized per unit biomass (e.g. cells, Chl, mg N, mg protein, dry
Waste
Sample
Injector
Detector
Analysis
Carrier
gas
Flow
controller
Time
C
2 H
4 L -1
h -1
C
2
H
2
Gas
Liquid
Sealed Assay
Vessel
Fig. 5.2 The C 2 H 2 reduction method (Breitbarth et  al. 2004; Capone 1993; Capone and
Montoya 2001)
5 Measurements of Organism Abundances and Activities