ADV06-15_1-412

129 / 413

along with minimum contamination, discrimination, and limits of
detection are required so that biological differences are not
obscured by analytical artifacts and variability.
Sample preparation is both the most critical step and the Achilles
heel. To preserve the integrity of the signal I have to sample what
the dogs do: the volatiles in the air around a scent mark. Solid
phase microextraction (SPME) and adsorption/thermal desorption
looked promising, but yielded too many peaks from contaminants
and too few from wild dogs. A simpler system was required to
reduce contamination, variability, and analytical artifacts. Direct
thermal desorption from urine-marked soil and cryotrapping with
sample flow paths of glass and fused silica has provided the clean-
est chromatograms so far. In nature, the scent marks are still active
on hot, dry sand; therefore, samples can be dried prior to desorp-
tion to prevent icing of the cryotrap and then desorbed at 60°C.
The complexity of most mammal odors puts them well inside the
Giddings zone, where at least 20% of chromatographic peaks over-
lap; not surprisingly, a dog mark chromatogram is so complex it has
no clean baseline. Overlapping peaks cannot be properly quanti-
fied or identified and most failures to find an MS library match are
due to coelutions that produce a mixed mass spectrum—only a
minority of those without matches are new and, therefore, exciting
compounds. To get cleanly resolved peaks, I will be using two-
dimensional GC to transfer incompletely separated peaks from one
column to another column with complementary selectivity.
Identifying everything in scent mark odor is unnecessary and
impractical; the spotlight needs to fall on the few compounds that
send the message. The critical challenge then is to differentiate the
biologically relevant signal from the chemical noise, and this is
where close links between the laboratory and the field operations
play an absolutely critical role. Only dominant dogs produce territo-
rial marks, so the signaling compounds will be present in their
marks, but absent from subordinates’marks. The marks withstand
65K temperature differences in the soil substrate between midwin-
ter midnights and summer afternoons. The marks last for at least six
weeks and their emissions of territorial semiochemicals should be
stable for at least as long. Without a detailed behavioral and social
context for each sample it would be impossible to recognize the
semiochemicals among the forest of extraneous peaks.
The wild dog boundary semiochemicals have to stand out against
a background of the millions of natural chemicals that permeate
the environment, and so I expect them not to be common con-
stituents of mammal scent marks, feces or urine, or volatiles from
plants or soil. Library searches of integer resolution mass spectra
will eliminate compounds that are known to come from these
sources.
Now that the sampling and separation conditions are worked out,
in the months to come I will be running scent mark samples from
several dogs in different packs searching for a peak, or a pattern of
peaks that is present only in the marks of dominant animals, that
stays the same with time and temperature, and that is not part of
the environmental background. When I find it (or them) the next
challenge will be to identify the compound(s). That will be a story
for another time.
For more information on the BPCT BioBoundaries project and
African wild dog research, visit or
.
Travels in South Africa
Jack Cochran, Restek’s Director of New Business and
Technology, recently took these pictures on a photo safari while
visiting South Africa to give seminars and collaborate on
research projects. Jack was invited by ChromSA, the
Chromatography Division of the South African Chemical Institute,
to teach a course called, “Improving Your Gas Chromatographic
Analyses.” Following this and other speaking engagements at
universities across the country, Jack spent several weeks work-
ing at the National Metrology Institute of South Africa on
QuEChERS, GCxGC/TOFMS, PCB and dioxin analyses, on-column
injection techniques, and various other gas chromatography
projects at the invitation of Jayne de Vos.
19
Website : E-mail : TelNo : 03 9762 2034 . . . in AUSTRALIA