CO2_2016 - page 12

10
Chimica Oggi - Chemistry Today
- vol. 34(2) March/April 2016
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which in turn was connected to the downstream union. In
terms of flow resistance, a 19 cm × 0.18 mm ID + 10 cm × 0.25
mm ID combination of capillaries is equivalent to an 80 cm ×
0.25 mm ID column. The lower flow resistance at the
upstream union will generate a pressure pulse (during
re-injection), thus extending the stop-flow period and
causing backflush.
The AC experiment was carried out using the same pressure
conditions as with the SC one; the
2
D flow, during
accumulation period (about 87% of the modulation period),
was calculated to be approx. ≈ 4 mL min
-1
, and increased to
approx. ≈ 5 mL min
-1
, during re-injection. The pressures
applied generated an LV during accumulation of 3.0 cm s
-1
,
while the LV during the 700-ms re-injection period reached 32
cm s
-1
. The modulation process this time was acceptable as
can be seen in the expansion illustrated in Figure 7B (C
9
). The
satisfactory result was confirmed by subjecting a sample of
Artemisia essential oil to FM GC×GC-qMS analysis.
CONCLUSION
On the basis of the results herein described, it can be
concluded that there are currently improved analytical
possibilities if the combinations of FM GC×GC with various
forms of MS are considered.
Further investigations, in all probability, will not be devoted to
a further decrease of gas flows (separations in the second
dimension would be too slow), but rather to develop and
propose an FM GC×GC system, capable of providing the
best possible separation performance.
Figure 7.
(A) Raw
chromatogram
expansion
showing the
modulation of C9
alkane at a 2D
flow of ≈ 5 mL
min-1 (SC). (B)
Raw
chromatogram
expansion
showing the
modulation of C9
alkane at a 2D
flow of ≈ 4 mL
min-1 (AC).
Reproduced with
permission from
Elsevier
(Franchina F.A.,
Maimone M., et
al., J.
Chromatogr. A
2016, 1441, 134–
139).
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