Comprehensive GC System Based on
Flow Modulation for the 7890A GC
Application Brief
Introduction
Power to separate in second column
In reality, some correlation in retention
A hardware solution is available on the 7890A for ALS
Conventional GC characteristics will be present between
the practice of comprehensive GC. The system uses the two columns.
a capillary flow modulator controlled by the 7890A Column 1
GC. The system is offered with factory checkout
using an FID detector. Other detectors, preferably Modulator
those operating at 50 Hz or greater, can be used.
Fast GC
Column 2
Comprehensive two-dimensional (2D) GC, or
GCxGC, is a powerful technique that can be used to Peak capacity is the maximum number of
Detector
equally resolved peaks that can be obtained
separate very complex mixtures, such as those in a given time, usually the entire run. The
found in the hydrocarbon processing, environmen- classic argument made is that GCxGC
increases peak capacity over what is
tal, and food/fragrance industries. possible with a one-dimensional separation.
The method uses two columns, typically of very dif-
ferent polarities, installed in series with a modula- Comprehensive 2D GC uses a primary column (conven-
tor in between. The second column is much shorter tional separation), a flow modulator, a second column
(very fast separation), and a fast detector.
than the first column to effect a fast separation.
The entire assembly is located inside the GC oven. This technique provides a second dimension of
information that can increase the peak resolution
The modulator performs three functions: and capacity.
A number of different modulator designs have
1. It collects effluent from the first column been described in the literature, most relying on
for a fraction of the time equal to peak thermal cycling to focus the bands from the first
width. For example, if a peak from column column and release them into the second column.
one is six seconds wide, the modulator will Some disadvantages to this approach are:
accumulate material every two to three
seconds, thereby dividing the peak from • Large usage of expensive cryogenic gases
the first column into two or three “cuts.” leading to a high cost of analysis
2. It focuses the material collected from each • Complexity of the hardware
cut into a very narrow band through flow • Longer analysis times
compression.
Agilent’s proprietary Capillary Flow Technology
3. It introduces the bands sequentially onto
and fourth-generation Electronic Pneumatics Con-
the second column, resulting in additional
trol (EPC) enable the use of a differential flow mod-
separation for each band injected onto the
ulator to conduct comprehensive 2D-GC without
second column.
the use of cryogenic gases or complex hardware.
The key to operation is the flow differential (typi- The primary column effluent enters the modulator’s
cally 20 to 1) between the second and first columns, top tee connection and flows into the collection
respectively. This compresses and focuses the ana- channel. The analytes from this column enter one
lytes present in any given modulation “inject” pulse end of the collection channel. Hydrogen flow from
into the second column. Precise timing of the mod- the PCM/three-way micro valve exits the modula-
ulator is made possible by installing a driver board tor at the bottom tee and is sent to the second
in the Aux det 2 detector slot of the 7890A main- column.
frame. Split/splitless
inlet
The Capillary Flow Technology modulator uses a
deactivated, stainless steel structure with all flow Column 1
(25-30M)
splitters and the collector channel incorporated
internally in the device. It has low thermal mass so
Inject flow
it can track the oven temperature very closely, and direction
its GC oven location allows precise temperature 0.8 mL/min
H2 Collection
control without lag during programmed runs. All channel
external connections are made using Agilent’s Ulti- Modulation
valve
mate Union technology for leak-free operation and Column 2
extremely small, well-swept volumes. A micro (5M)
three-way solenoid valve, installed on the side of FID
the gas chromatograph, connects to a pneumatics
control module (PCM) to accurately and precisely Flow Modulator approx. 21 mL/min
control the flows through the modulator.
Collection channel is
quickly “injected” into
The figures below illustrate the modulator. A second column in about
three-way solenoid valve receives a controlled 0.1 second
supply of hydrogen gas from a PCM. The periodic Flow rates and flow directions during the transfer or
switching of this three-way valve drives the modu- inject portion of the modulation cycle
lator. The precisely timed and synchronized
switching between the collect and inject states Inject or flush state (above): Hydrogen gas flow
directs discrete sample pulses continuously to the from the three-way solenoid valve is directed to
second column for additional fast separation the top tee. A high flow of typically 20 mL/min for
throughout the chromatographic run. Both about 0.1 second rapidly flushes the collection
columns are run in constant flow mode. For opti- channel, transferring material in a very narrow
mal performance, injection size and split ratio band onto the second column where any analytes
should be carefully adjusted to avoid overloading, collected in the channel undergo rapid separation.
which can lead to excessive peak tailing.
Split/splitless What is required:
inlet • Agilent 7890A GC with firmware version A.04.06 or higher
• FID with 200 Hz data collection rate or other fast detector
Column 1
(25-30M) • Split/splitless inlet
• Capillary Flow Technology modulator option or accessory
• Capillary Flow Technology modulator checkout kit
0.8 mL/min
H2 Collection • Pneumatics control module (PCM)
channel
• Agilent GC ChemStation B.03.02 or other data collection and
Modulation
valve analysis system that can control the flow modulator cycle
Column 2
Collect flow (5M) • 30-m × 0.25-mm × 0.25-µm DB-5ms column (included with
direction option or accessory)
FID
• 5-m × 0.25-mm × 0.15-µm INNOWax column (included with
option or accessory)
Flow Modulator approx. 21 mL/min
• 2D data analysis software, GC Image recommended
Flow rates and flow directions during the load or collect (not provided by Agilent)
portion of the modulation cycle
• Internal column nuts and SilTite ferrules
Load or collect state (above): At the beginning of
this state, the collection channel is filled with
hydrogen gas from a previous injection cycle flush.
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Ordering Information
Description Part number
7890A GC with Capillary Flow Technology Modulator (requires checkout kit) G3440A Option 887 or accessory G3486A
7890A GC with 200 Hz FID G3440A Option 211 or accessory G3462A
7890A GC with split/splitless inlet G3440A Option 112 or accessory G3452A
Capillary Flow Technology modulator checkout kit G3487A
PCM for 7890A GC G3440A Option 309 or accessory G3471A
SilTite metal ferrules, 1/16-in × 0.4-mm id, 10/pk, includes 2 column nuts 5184-3569
Agilent 32-bit ChemStation for 1 GC G2070BA
Agilent 32-bit ChemStation Bundle for 1 GC includes: G1875BA
– G2070BA 32-bit ChemStation software
– Computer with monitor and Windows operating system
– Printer
2D GC software www.zoex.com
Recommend GC Image software, which can be purchased from Zoex Corporation
Application Examples the possibilities. The GC Image software package
was used for processing the ChemStation data.
Several applications are shown. Note that primary
1. B20 biodiesel based on soy FAMES. Section of
column lengths have been chosen to give optimal
the 2D image showing the C16 and C18 FAMES
results. While the 30M column that is shipped with
is shown.
the system is an excellent choice for a wide range
of applications, other lengths can be used to opti- Column 1: 60 m × 0.25 mm × 0.10 µm DB-5ms
mize a given separation. Various columns have
Column 2: 5 m × 0.25 mm × 0.15 µm INNOWax
been used in these examples to illustrate some of
Modulation: 1.40 s load, 0.10 s inject
C18:1
C16 C18:2
C18:0
C18:3
3
2. Complete 2D image of a sample of heavy gaso-
line. Each series of substituted 1-ring aromatics
is well separated, making hydrocarbon class
grouping possible.
Column 1: 60 m × 0.25 mm × 0.10 µm DB-5ms
Column 2: 5 m × 0.25 mm × 0.15 µm INNOWax
Modulation: 1.40 s load, 0.10 s inject
3. Lime oil 2D image.
Column 1: 15 m × 0.25 m × 0.25 µm DB-5ms
Column 2: 5 m × 0.25 mm × 0.15 µm DB-17HT
Modulation: 1.40 s load, 0.10 s inject
Limonene
C20 reference
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Thermal vs. Flow Modulation
Since competitors offer only systems based on
thermal modulation, the following table summarizes
the key points about the respective approaches of
thermal vs. flow modulation.
Thermal modulation Differential Flow modulation
Cryo-focusing provides potentially Peak widths comparable to thermal. Usually no more than 20% wider.
narrower peaks in second dimension Many users want to sum regions of peaks where peak width is not as critical
Lower flows – Can be used with high- MSD can be used with a splitter over limited scan range
vacuum detectors (TOF)
Large consumption of cryogen No cryogen required
Complex hardware design, set-up, Simple, reliable Capillary Flow Technology based hardware; small thermal foot
and maintenance print
Long chromatographic runs required for Run times comparable to a 1D separation
best performance
System price (estimate) Agilent system approximately $60K (list)
$60 to $70K
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www.agilent.com/chem
For More Information
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visit our Web site at www.agilent.com/chem.
Agilent shall not be liable for errors contained herein or for incidental or consequential
damages in connection with the furnishing, performance, or use of this material.
Information, descriptions, and specifications in this publication are subject to change
without notice.
© Agilent Technologies, Inc. 2008
Printed in the USA
April 1, 2008
5989-8060EN
