Worldwide Solutions - February 2008 - (Page 7) GERSTEL Solutions Worldwide Application ew fruits are seen as symbol of so many quisition is needed for sufficient peak defdifferent things and few carry as many inition and accuracy of results, for this, an different meanings across human cul- MSD is needed that offers faster scan rates. tures as apples. Among other things, apples The RIC used a 6890 GC combined with symbolize fertility, love, and ties to home, a state-of-the-art 5975 Quadropole MSD family and country. Lest we forget, apples from Agilent Technologies for this work. The 5975 enables data acquisiequally symbolize temptation and tion rates of up to 21 Hz, 21 full original sin. In the U.S., the sayscans per second, while maintaining “as American as apple pie” reing mass spectral data quality. fers to apples as almost a symbol To enable fast heating rates, the of the good American life. SymGC was equipped with a Modubolism aside, one can still say aplar Accelerated Column Heater ples are healthy and tasty, provid(MACH) from GERSTEL. MACH ed that they have been allowed is based on column heating modto fully ripen in the proper way. ules that enable direct resistive Most frequent consumers of apheating at rates of up to 1800 °C / ples have sufficient experience to Andreas Hoffmann, min. Not only is the column heatrecognize a good, ripe and well Manager Analytical developed apple when confront- Services (Application), ing step accelerated by MACH: The GC column cools down from ed with one. The speed at which GERSTEL 240 °C to 40 °C in as little as 30 an experienced person can make seconds, depending on the column length. a correct visual and olfactory assessment of an apple cannot be beaten by analytical in- Since there is little material that needs heating or cooling, the GC equilibration time strumentation to date. can also be cut to near zero. The overall When, however, a brand name product relies on consistently delivering the same result: Ultra-short GC cycle times and a accepted great taste batch after batch - year significant increase in productivity and in year out - more than subjective selection throughput. by humans will be required: Enter chemical analysis in the form of gas chromatography MACH based on Low Thermal coupled with mass selective detection (GC/ Mass (LTM) technology MSD). Professor Pat Sandra and his team at Unlike a traditional GC oven, the MACH the RIC accepted the challenge to speed up module has no insulation material and no the analysis of flavor compounds in apples metal based oven chamber that needs to used for a brand name product. Using a fast be heated or cooled along with the column GC column module, the Modular Acceler- over the GC cycle. MACH is controlled ated Column Heater (MACH) from GER- from the Agilent Technologies ChemSTEL, the RIC team was able to speed up Station Software or directly through the apple flavor analysis by a factor of 10 com- MAESTRO software. Andreas Hoffmann, pared with the customer analysis method, GERSTEL Applications Manager: “We don’t reducing the cycle time to 4.5 minutes. drill a hole in the GC oven door to mount the MACH modules; the door is replaced Easy GC modification with a dedicated oven door that holds up improves performance to 4 MACH modules.” It takes only around The speed of capillary GC analysis can be 30 minutes to upgrade a 6890 or 7890 GC improved significantly by increasing the to MACH, getting it ready to perform fastspeed of temperature programming. Ad- er. “The column module is simply mounted ditional factors are at play, of course. Shortfrom the er columns with smaller i.d. provide a big boost. Smaller columns in return require improved pneumatic control at higher carrier gas pressures. Further, a GC inlet is needed that offers adequate dimensions (small internal volume) and a split vent. These properties enable the inlet to deliver analytes to the GC column in a narrow band, the best possible start for high-quality fast separations. Accelerating the GC separation process of course has consequences “downstream”: Faster data ac- F outside through an opening in the door, not inside the GC oven. “This has the added benefit that when operating the GC oven isothermally at the maximum temperature required for the analysis, no special accessories are required to heat the end of the column or the transfer capillaries to the standard GC injector or standard GC detector.” First peel your apple, and then apply automated sample preparation and high performance column technology This is how the RIC scientists approached the task: An apple was peeled and homogenized using an Ultraturrax™ blender. A ten gram sample of the resulting apple sauce, or compote, was weighed into a 20 mL vial, which was capped and placed in the GERSTEL MultiPurpose Sampler (MPS) tray. Sample preparation and sample introduction to the GC/MSD system was performed by the MPS using the Headspace Solid Phase Micro Extraction (HS-SPME) technique. The SPME fibre, coated with 100 µm polydimethylsiloxane (PDMS), was placed in the sample headspace for five minutes to extract the volatile analytes. The sample temperature was held at 25 °C. The fibre was subsequently desorbed at 250 °C for 30 seconds. For maximum productivity, the MPS was set to PrepAhead mode providing overlapping sample preparation and chromatography. In PrepAhead mode, samples are prepared during the GC-run of the preceding sample. When the GC becomes ready, the next sample has been prepared and is ready to be injected. This approach helps to ensure that the GC /MSD system is never idle providing maximum productivity and system utilization. The inlet, a Cooled Injection System (CIS) from GERSTEL was fitted with a 1.5 mm i.d. deactivated liner and set to split mode with a split ratio of 3:1. The Helium carrier gas was initially set to a constant pressure of 390 kPa and the column flow was set to 0.8 mL/min, which translated to a flow of 3 mL/min through the liner, sufficient for fast analyte transfer onto the GC column. The resulting sensitivity met all QC requirements. The inlet was connected to the column in the MACH module via a 20 cm long, 100 µm i.d. deactivated fused silica capillary. The transfer capillary was kept inside the GC oven at 250 °C isothermal. The GERSTEL Solutions Worldwide – February 2008 7
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