1
MODERN GAS CHROMATOGRAPHIC EQUIPMENT DESIGN 1 Massimo Santoro, 1 Paolo Magni, 1 Fausto Pigozzo, 2 Danilo Pierone 1 Thermo Fisher Scientific, Milan, Italy 2 Nova 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-C 100 (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.
