CO2_2016 - page 8

Chimica Oggi - Chemistry Today
- vol. 34(2) March/April 2016
KEYWORDS: Comprehensive two-dimensional gas chromatography, flow modulation, mass spectrometry, method optimization.
The present short review (based on research performed by the authors reported above) describes recent
evolution (2011-2016 period) of flow modulation (FM) comprehensive two-dimensional gas
chromatography (GC×GC), within the context of mass spectrometry (MS) hyphenation. Specifically, it will be shown how intensive
research on an FM model has enabled a great reduction in gas flows (down to approx. 4 mL min-1), making the combination of
GC×GC and MS now much easier.
Recent evolution of flow-modulation
comprehensive gas chromatography
within the context of mass spectrometry hyphenation
Comprehensive two-dimensional gas chromatography
(GC×GC) is now a well-established multidimensional GC
method, it being introduced nearly 25 years ago (1). In
GC×GC, a device named modulator enables the continuous
and sequential transfer of “heart-cuts” from a primary to a
secondary column. Separations in the second dimension (
are usually very rapid, normally less than 10 s. GC×GC data
are visualized in a two-
dimension (2D) format, with
peaks characterized by an
ellipse shape, and by first and
second-dimension retention
times. If desired, more details on
GC×GC basic theory can be
found in the literature (2).
The modulators used in GC×GC
experiments can be classified
into two main groups, namely
thermal (normally cryogenic) or
flow-based systems. Cryogenic
modulators are by far the most
commonly used, even though
they remain an expensive
choice. For such a reason, the
low hardware and operational
costs of flow modulation (FM) makes such an option an
attractive one. One of the main reported disadvantages of
FM has been the generation of excessively-high gas flows
(> 20 mL min
), with consequential difficulties when using
mass spectrometry (MS) detection (3).
The most important FM device (in the present authors’
opinion), was first reported in 2006 (4); the interface consisted
of three uncoated fused-silica columns, two micro T-unions
and a three-way solenoid valve (located outside the GC
oven), with the latter linked to an auxiliary pressure (AUX)
source (Figure 1).
The output ports of the solenoid valve were connected to the
unions by using two metal branches, connected to fused-silica
segments. One of the T-unions
was linked to the first-dimension
(1D) outlet (upstream), while the
other directed the flow to the
second column (downstream).
A fused-silica segment acted as
accumulation loop, and bridged
the two unions. When the FM was
in the “accumulation” mode, the
auxiliary flow (20 mL min-1) was
directed to the downstream
union, and the primary-column
effluent (approx. 1 mL min-1)
flowed through the loop; it is
worthy of note that the
accumulation period (1.4 s) was
lower than the time necessary for
the effluent to reach the
downstream union (about 1.5 s). When the solenoid valve was
switched for a brief period (100 ms), the auxiliary flow flushed the
content of the loop onto the second dimension (re-injection
mode). It is noteworthy that the 1D flow is temporarily interrupted
during the re-injection step, it being caused by a pressure pulse
*Corresponding author
1. Chromaleont s.r.l., c/o University of Messina, Polo Annunziata,
viale Annunziata, 98168, Messina, Italy
2. “Dipartimento di Scienze Chimiche, Biologiche, Farmaceutiche ed Ambientali”,
University of Messina, Polo Annunziata, viale Annunziata, 98168, Messina, Italy
3. Università Campus Bio-medico of Rome, via Álvaro del Portillo 21, 00128 Roma, Italy
Peter Q. Tranchida
Figure 1.
Model of flowmodulator introduced by Seeley and
co-authors [4]. Abbreviations: PINJ = injector pressure; Pz up = pressure
at the upstream point z; Pz down = pressure at the downstream point z;
PAUX = auxiliary pressure. Adapted from Elsevier (Franchina F.A.,
Maimone M., et al., J. Chromatogr. A 2016, 1441, 134–139).
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