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MODERN GAS CHROMATOGRAPHIC EQUIPMENT DESIGN
1Massimo Santoro, 1Paolo Magni, 1Fausto Pigozzo, 2Danilo Pierone
1Thermo Fisher Scientific, Milan, Italy 2Nova Analítica, SP, Br
Overview
Purpose: To show an innovative approach to GC instrumentation
design which allows easy configuration change and/or upgrade.
Method: The fundamental Gas Chromatograph components are
independent modules which are pooled to produce the desired analytical
layout for the specific application.
Results: Preservation of the analytical performances, also for most
common critical GC and GC-MS applications, is demonstrated.
Conclusion The new approach to gas chromatographic equipment design
redefines GC usability:
• User exchangeability of injectors/detectors.
• Easily match instrument configuration to application needs.
• Eliminate routine maintenance downtime by using spare modules.
Design challenges were overcome thanks to miniaturization and an
innovative thermal management of system components.
System validation, even for the most critical applications, confirms
that “instant connect” modularity is implemented without
compromising analytical performance.
Modular design and miniaturization enable integration of a backflush
system into the injector module and optimization of large volume
splitless injection.
All trademarks are the property of Thermo Fisher Scientific and its subsidiaries.
This information is not intended to encourage use of these products in any manners that might
infringe the intellectual property rights of others.
From the conventional to a new GC design
Introduction Gas chromatography is used for a wide number of applications and often
requires specific hardware configurations with appropriate inlets and/or
detectors for the matrix and target analytes of interest. Changing a
system configuration to address a new analytical need is a difficult
operation and often results in a new system requirement.
In this poster, an innovative approach to GC instrumentation design is
shown which allows easy configuration change and/or upgrade. The
technological choices and implications intrinsic of this innovative modular
approach to GC instrumentation design is highlighted. Particularly
important are the design aspects of the injector and detector modules,
their couplings with the high temperature column oven, the
miniaturization of pneumatics circuits, and electrical-mechanical
components.
Quick recovery after module replacement
Each module incorporates:
Injector (or detector) body.
Miniaturized IEC (Integrated Electronic gas
Control).
Gas manifolds and connections, restrictions and
electronic valves built-in.
Electronics for temperature and gas control, for
signal amplifier and A/D conversion.
Modular Approach Similar to modern HPLC instrumentation, in the new GC design
philosophy the fundamental instrument components are independent
modules which are pooled to produce the desired analytical layout for
the specific application.
“Instant Connect Modules”: injectors and
detectors are user installable in only 2 min,
just removing three screws.
Modules can be quickly combined by the user
to build up the configuration required by the
application or to postpone maintenance, using
spare modules. Maintenance can be done off-
line on the module while GC still runs.
Every injector and detector is compact and self-
sufficient, containing the Integrated Electronic
gas Control (IEC) and all hardware and
electronics (SSL injector shown here).
Last run with old module First run after changing module
20 min later
Backflush Integration into SSL and PTV Inlet Modules
The entire pneumatic circuit is integrated in the injector module.
No tubing nor fittings are used, minimizing risks of leaks and
eliminating method complexity.
A 3-way valve diverts main stream of carrier gas while flow restrictors
maintain a minimum purge flow through the inlet line/bkf lines when
not in use (to avoid dead volume effects).
Modular GC: Three Main Design Challenges
The conventional GC equipment design requires specific injectors and
detectors to run different GC applications. Injectors and detectors bodies
are assembled on oven top deck and require additional pneumatic and
specific electronics. The large number of options brings to thousands of
possible GC configurations. Typically, systems are manufactured based
on application requirements and upgrades or changes in configuration at
site is difficult, time consuming and requires service engineers.
A new modular GC system was developed where the inlets and
detectors are modular devices incorporating all flow, pressure,
temperature, and signal control. Modules are then housed onto a GC
oven, connecting to gas feeds and to the analytical column.
1. Miniaturization of components: electronic boards and
pneumatic circuits were miniaturized. All pneumatic circuit was
integrated in a manifold with no or minimum use of tubing or fittings
minimizing risks of leaks.
All gas channels are machined into the manifold
Flow restrictors are housed directly into
the manifold. Manifold temperature is
measured in real time and used for
proper flow compensation
Seal to valve and sensor is made by
high quality o-rings
2. Temperature constrains:
A special copper plate extracts the
heat leaving the oven top insulation
and dissipate it through an heat
sink.
Oven top deck remains close to
ambient temperature even when
the oven is heated at 450 °C.
The fan used to force air on the
heat sink forces air for the module
ventilation and for a constant active
cooling of electronic components.
Forced air enters modules from the
back and keeps electronics cool.
Air is then vented through the
injector box hole creating a barrier
against the heat produced by the
hot injector .
The air vent helps in keeping the
septum head cool without affecting
the internal inlet temperature profile
Module base is cooled by the oven
top deck copper plate.
Same air path is used for detectors.
3. Ensuring reliable connections:
Gas connection for modules’
manifolds
Electrical connections
Pneumatic connection
• Dependably mating block with
high-quality o-rings.
Electrical connection
• Standard off-the-shelf 25-pins
connectors adopted.
Applications Validation
Precision/Accuracy:
Retention times
run C10 C20 C40
1 2.395 9.047 16.367
2 2.397 9.047 16.367
3 2.395 9.045 16.368
4 2.397 9.048 16.370
5 2.397 9.045 16.368
6 2.397 9.045 16.367
7 2.395 9.045 16.365
8 2.395 9.047 16.368
9 2.395 9.047 16.368
10 2.393 9.045 16.367
Mean 2.396 9.046 16.368
SD 0.001 0.001 0.001
Peak areas
run C10 C20 C40
1 2787978 2822489 2284465
2 2779199 2821282 2287681
3 2774121 2819618 2284208
4 2785360 2820062 2278054
5 2784181 2831367 2300419
6 2792274 2836730 2316013
7 2796017 2828151 2304649
8 2815168 2853598 2311401
9 2790653 2835701 2305217
10 2811036 2857141 2300863
Mean 2791599 2832614 2297297
SD 12998 13529 12855
RSD% 0.47 0.48 0.56
Component Recovery vs C20%
C12 101.2
C14 99.3
C16 101.0
C18 99.1
C20 100.0
C22 99.8
C24 99.6
C26 99.2
C28 100.0
C30 104.8
C32 101.4
C34 100.0
C36 101.2
C38 99.8
C40 100.1
Retention times
SD ≤1/1000 minute
Absolute peak area
RSD% «1%
Recovery at 100%
up to n-C40
Elution of high boiling is not affected by injectors and detectors
modularity.
n-alkanes up to C40 in splitless: full recovery and excellent precision.
ASTM D7169 HT-SimDist:
Critical very high temperature application.
Calibration up to C100 (B.P. 720°C) using PTV Injector.
Elution of n-C100 (Polywax 1000 sample).
Injector module replacement with fast recovery of operating conditions.
Modules store all their calibration information allowing minimum
variation if replaced on a system.
No need for method re-calibration.
Module to Module Repeatability:
Retention Time Std. Dev. always in the range of 1/1000 or less.
Variation in retention times are in the range of 1/100 of a minute
or less.
* Data referred to a sequence of 10 injections
* Data referred to a sequence of 10 injections
Peak Area %RSD always below 1%.
Variation in absolute peak area in the range of few % changing
either the inlet or the FID detector.
Additional value of miniaturization
Splitless Large Volume Injection
Compact inlet design enables low dead volume in the
pneumatic circuit for optimal Splitless performance
even with large sample volumes (up to 50 ml).
High boiling components
backflushed and vented out of
the split vent avoiding
contamination of the separation
column.
Excellent reproducibility.
Simplification of pneumatic
method and layout without
additional valve controls.
Capillary columns adopted.
ASTM 3606 Application
using SSL with BKF:
(a) (b)
(a) GC Equipment Design since 1955; (b) A new Modular Approach to GC design.