Separation Times, Vol. 22, Issue 2 

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Speed cycle times and enhance multidimensional gas chromatography with LTM technology

By Dave Johnson
Agilent Gas Chromatography Product Manager

Obtaining faster GC and GC/MS analysis times has been the topic of many seminars and publications developed by Agilent. [1, 2, 3] However effective these techniques may be, the oven ramp and cool down rates of a conventional oven-bath gas chromatograph may still keep you from achieving substantial increases in analytical cycle times.

Thanks to the acquisition of RVM Scientific in June 2008, Agilent can now provide a patented technology for direct, rapid heating and cooling of fused silica capillary columns. This low thermal mass technology (LTM) speeds GC and GC/MS analytical cycle times and – when combined with Agilent’s capillary flow technology – reduces column maintenance to expand the number of potential analytical applications, as well as providing significant new capabilities in multidimensional GC.

	Figure 1. The key to LTM technology. LTM weaves direct heating and temperature-sensing components around standard fused-silica capillary columns (up to 30 meters) for rapid heating and cooling.

Advantages of LTM technology

LTM technology combines standard, fused silica capillary GC columns with separate heating, temperature-sensing and insulating elements to form a modular gas chromatographic system. Because this system resides outside the GC oven, the high thermal mass GC oven walls and door do not need to be temperature cycled. This means the LTM system heats and cools the relatively low thermal mass column quickly and consumes far less power than a conventional air-bath GC oven. (See Figure 1.)

Heating a capillary column directly allows for extremely fast ramp rates, as fast as 1800°C/min. Naturally, chromatography rates depend on column mass, configuration and void times, and are typically lower – yet still much faster than conventional air-bath oven rates. [4] The LTM system’s cooling capabilities are equally fast, less than one minute for some configurations, further reducing analytical cycle times. (See Figure 2.) This heating and cooling time has no negative affect on results because the system provides precise, uniform heating, yielding retention time repeatability that is comparable to conventional GC.

Figure 2. Typical cooling times for standard (5-inch) LTM column modules of typical lengths are significantly faster than a conventional GC oven. (Click here to see this image larger.)

Figure 3. Traditional run time for an alkane standard for TPH analysis is reduced by a factor of 10x to less than 3 minutes utilizing the LTM system’s accelerated ramp rates (200°C/min) and a shorter column. [5] (Click here to see this image larger.)

Figure 4. Fast simulated distillation of cracked gas oil accomplished in less than 3 minutes using a temperature ramp of 150°C/min. A 10-run overlay shows outstanding repeatability. [6] (Click here to see this image larger.)

Figure 5. In this PAH analysis by LTM/GC/MS, the upper chromatogram shows how soil extracts contaminate the column in just one run. The bottom chromatogram shows how backflushing helps to keep the column contamination free. [7] (Click here to see this image larger.)

Figure 6. The top chromatogram shows the signal from a natural lavender oil analysis with one linalool peak – indicating it is from a natural source. The bottom chromatogram shows an equal amount of enantiomers (a racemic mixture) – indicating that it was from a synthetic source. [10] (Click here to see this image larger.)

LTM’s faster cycle times benefit many applications

LTM’s rapid thermal cycling is ideal for labs where faster cycle times can reduce the cost per analysis. The LTM system’s ability to accelerate temperature ramp rates far beyond conventional GC can greatly reduce analysis times (Figure 3), while providing resolution and quantitation comparable to traditional methods.

In Figure 4 you see how an LTM application handles the simulated distillation analysis of cracked gas oil 6 times faster than the conventional ASTM D2887 procedure. This shorter analytical cycle time lets you get critical information back to operations faster, to facilitate making process decisions in a more timely manner.

Backflushing maximizes column life

When analyzing food or soil extracts, an LTM column module can be easily protected by using guard columns, along with backflushing of high boiling sample contaminants using a purged capillary flow technology device (Figure 5). While these dirty samples can contaminate a column and cause baseline increases that affect subsequent runs, backflushing helps to keep the column contamination free, which also reduces potential for carryover and lengthens column life. In addition, run times are reduced by avoiding the bake-out times normally required to remove contaminants that elute after the last peak of interest.

2-D multidimensional analysis using LTM Technology

Coupling capillary flow technologies with LTM technology allows you to address even more difficult challenges of analyzing for trace compounds in complex matrices, found in chemical processing, flavors, fragrances and pharmaceutical applications. The LTM system’s ability to temperature program multiple LTM column modules, operating simultaneously with different temperature ramp profiles, provides new capabilities for multidimensional GC. [8, 9]

Figure 6 shows a chiral analysis of linalool in fragrance samples. Analysis of analytes in complex samples usually requires a broad temperature program to separate target compounds and elute highly retained components. But most chiral columns exhibit lower selectivity, high bleed and decreased lifetimes at elevated temperatures. A traditional column (in the GC oven or an Agilent J&W LTM column module) provides a 1st stage separation of compounds. The compounds of interest are then separated from sample background by heartcutting to a chiral column in an Agilent J&W LTM column module operating at a lower temperature. This achieves optimal chiral separations while decreasing analysis cycle times and increasing chiral column lifetime.

Learn more about the advantages of LTM technology

The applications illustrated here demonstrate how LTM technology’s direct, rapid heating and cooling can greatly reduce GC and GC/MS analytical cycle times. In combination with Agilent’s capillary flow technology, one can reduce column maintenance enabling LTM technology to be used in an even wider range of analytical applications as well as provide significant new capabilities in multidimensional GC.

References

1. Ken Lynham, Practical Faster GC Applications with High-Efficiency GC Columns and Method Translation Software, Agilent Technologies, March 4, 2008, Seminar/Article
2. Mike Szelewski, Significant Cycle Time Reduction Using the Agilent 7890A/5975C GC/MSD for EPA Method 8270, Agilent Technologies Inc., 5989-6026EN
3. Lisa Wool & and Daron Decker, Practical Fast Gas Chromatography for Contract Laboratory Program Pesticide Analysis, Journal of Chromatographic Science, Vol. 40 September 2002
4. Agilent Low Thermal Mass (LTM) System for Gas Chromatography Datasheet, Agilent Technologies Inc., 5989-8711EN
5. Wei Luan & Mike Szelewski, Ultra-Fast Total Petroleum Hydrocarbons (TPH) Analysis with Agilent Low Thermal Mass (LTM) GC and Simultaneous Dual-Tower Injection, Agilent Technologies Inc., 5990-3201EN
6. ChunXiao Wang, Roger Firor and Paul Tripp, Fast Hydrocarbon and Sulfur Simulated Distillation Using the Agilent Low Thermal Mass (LTM) System on the 7890A GC and 355 Sulfur Chemiluminescence Detector, Agilent Technologies Inc., 5990-3174EN
7. Frank David (Research Institute for Chromatography, Kortrijk, Belgium) and Matthew Klee (Agilent Technologies), Fast Analysis of Polynuclear Aromatic Hydrocarbons Using Agilent Low Thermal Mass (LTM) GC/MS and Capillary Flow Technology QuickSwap for Backflush, 5990-3451EN
8. Frank David (Research Institute for Chromatography, Kortrijk, Belgium) and Matthew Klee (Agilent Technologies), Analysis of Suspected Flavor and Fragrance Allergens in Perfumes using Two-dimensional GC with Independent Column Temperature Control using an LTM Oven Module, 5990-3576EN
9. Jim Luong & Ronda Gras (Dow Chemical Canada, Fort Saskatchewan, Alberta Canada), Grace Yang (Dow Chemical China, Songjiang, Shanghai China), Hernan Cortes (Dow Chemical USA (Midland, MI USA), Robert Mustacich (RVM Scientific, Santa Barbara, CA USA), 2D LTM/CFT/GC using Deans Switch and LTM’s simultaneous /independent temperature programming of multiple LTM column modules, Journal of Separation Science 2008, ISSN 0021-9665, Volume 31, pp. 3385-3394
10. Frank David (Research Institute for Chromatography, Kortrijk, Belgium) and Matthew Klee (Agilent Technologies), Independent Column Temperature Control Using an LTM Oven Module for Improved Multidimensional Separation of Chiral Compounds, 5990-3428EN

© Agilent Technologies, Inc. 2009