The Future of GC Instrumentation From the 35th International Symposium on Capillary Chromatography (ISCC)

The 35th International Symposium on Capillary Chromatography (ISCC) was one of three parallel tracks featured at the Joint Congress 2011. The meeting was organized by CASSS and was held May 1–5 in San Diego, CA.

Instrumentation has a life cycle. Gas chromatographs are mature, so the cycle is probably 10–12 years. The Agilent 7890 gas chromatograph (Agilent Technologies, Palo Alto, CA) is over four years old, so the product planners are probably only starting to think about a replacement. This is the appropriate time for the technical leaders to offer advice. After all, when the 6890 replaced the 5890, backflushing was not offered.

Prof. Milton Lee (Brigham Young University, Provo, UT) chaired a session that was attended by approximately 100 gas chromatographers and meant to distill features and attributes that should be considered. As examples, Prof. Lee listed resistively heated columns, multidimensional GC, integrated (on-line) sample prep, smaller footprint, and smarter instruments that generate quality results, even when operated by nonspecialists.

Then Prof. Lee asked a panel of four experts (two vendors and two users) to make short presentations. Dow Chemical is the world’s largest user of gas chromatographs, with over 1000 active chromatographs. Thus, Prof. Lee selected the company’s Associate Technology Director & Global Separations Leader, Jim Luong (Dow Chemical Co., Fort Saskatchewan, Alberta, Canada) to report on a survey of GC users at Dow. Luong asked his colleagues to point out opportunities for inclusion in next-generation instruments. The list included:

  • Continuous development of planar microfluidics devices such as Agilent’s CFT and SGE’s (Ringwood, Victoria, Australia) wafers
  • Separation improvements

1) The column is the heart of chromatography and we are not at the level of inertness we should be

2) “It can’t be done” should not be a barrier

  • Reduced to the practice of multidimensional gas chromatography (2DGC and comprehensive 2DGC)
  • Advanced sample introduction system
  • Selective detectors (e.g., sulfur chemiluminescence detector, nitrogen chemilumisence detector, elemental combusion system for CHNOS [Costech, Valencia, CA], and Differential Mobility Detector [Agilent])

1) Little has changed on the status of GC detection for many years

  • Advances in miniaturization—articulating the needs is important
  • Software that is stable and improved over previous generations
  • Wizards to aid in setting up applications.

Luong quickly expanded on each of these points. When he mentioned the need for selective detectors, I thought about how different the world would be if the element-specific detectors, such as thermionic and photometric, became established before mass spectrometry grew dominant.

The second panelist was Dr. Hans-Gerd Janssen of Unilever (Vlaardingen, The Netherlands), who reported on the state-of-the-art in GC (Table 1). The current GC technology is not robust by contemporary standards. Columns age and MS filaments need replacement. Injectors and other fittings start to leak with temperature cycling. The instruments are slow, with cycle times in tens of minutes. Dr. Janssen is aware that cycle times can be reduced by 90% with modern technology. Other criticisms included difficulty to use, inflexibility, and lack of a clean interface between sample prep and the GC.

Figure 1 - Coefficients of thermal expansion for various materials in gas chromatography. Repeated thermal cycles from repeated temperature-programmed runs slowly accumulate stress and resulting movement, leading to leaks during repeated runs. (Courtesy of Brian Jones, Restek.)

Representing the column vendors, Brian Jones of Restek (Bellefonte, PA) followed with a thoughtful review of current needs. He cited an article in LC·GC from 14 years ago on the same topic,1 and added “Rugged, reliable separations that are tolerant of dirty samples. Reliable and easy connections for columns etc., especially in the hot zone; faster cycle times; faster detectors; true plug-and-play operation; columns with a higher Tmax; and more sensitive detection.” Brian went on to explain that leaks in the hot zone probably arise from the huge difference in thermal expansion of the components (Figure 1).

Stan Sterns, President of Valco Instruments Co. (Houston, TX), finished out the panel by showing examples of separations using the best of today’s technology, which includes temperature ramps of 1200 °C/min. Further, the temperature accuracy and reproducibility can be held to better than 0.2 °C. Run times are 90% shorter than big-box technology and more reproducible. One example showed a chromatogram of biodiesel in less than 2 min and pesticide residues in 40 sec (Figure 2). Cooldown was complete in 1 min, so the cycle time is less than 4 min injection-to-injection.

Figure 2 - Separation of pesticides using a 50 μm × 1 m VB-1 column and mini pulsed discharge detector. The column uses resistive heating. Cold spots are eliminated with Valco center tap technology. (Courtesy of Stan Sterns, Valco.)

Consumption of carrier and makeup gas and electricity is reduced by similar factors. A typical big-box GC consumes about 2 kW/hr. Air conditioning adds another 3 kW/hr. Over a year, this is 43,000 kW/hr. At $0.15 kW/hr, the electrical cost of a GC is about $6000/year. This does not count the cost of the operating gases for column flow and detectors, which probably adds another $1000/yr. Stan estimates that Valco’s technology reduces the operating cost per run by at least 90%.

Finally, Prof. Lee opened the discussion to the floor. The goal was to distill even more needs and ideas. Comments from the audience included:

The lecture by Prof. Robert Synovec (University of Washington, Seattle) earlier in the day showed that one common big-box GC was slow and inefficient for early-eluting peaks (Kʹ <4). Prof. Nick Snow (Seton Hall University, South Orange, NJ) concurred with the earlier presentation by Prof. Lee and Dr. Synovec, citing the need for better injection technology. Indeed, injection technology still seems to be a weak point, even after six generations of instruments. The injection process needs to be reengineered from the ground up to improve performance across the board. Particular needs included lower band broadening; robustness (leak free, especially with temperature cycling); and ease of use, particularly for column installation.

Resistive heating can suffer from cold spots due to nonuniform metal thickness. Stan Sterns countered that if the metal is correctly applied, cold spots are not a problem. Plus, one can use multiple zone heating to avoid creating cold spots at injectors, column-switching devices, and detectors. He mentioned center tap technology as a key design for heating the subsystems of a GC, including detectors, injectors, columns, and column switching.

Temperature programming inevitably entails trouble with leaks in the hot zone of the GC. What can be done? Stan responded with a description of a press fit connector made from gold-plated nickel that is rated at 70,000 psi. This enables quick, reliable, and robust connection of fused-silica tubing for various applications.

Based on his experience at Dow, Dr. Luong pointed out that the problems drive the solution, especially in mature market segments. Chromatography is still the best tool. Dr. Janssen commented that LC is now easier than GC, but both require continuous improvements in technology to meet market needs. Further, Dr. Janssen pointed out that despite that, the vast majority of critical analyses are conducted using well-known, mature techniques. In contrast, the emphasis of research in gas chromatography is aimed at areas other than practical.

At this point, I noticed that the discussion tipped from an academic recitation of technical needs and possible solutions to a session driven primarily by frustrations. Even today, the instruments are often more sophisticated than the average user, whether he/she is a technician, graduate student, scientist, or principal investigator using chromatography as part of the project. Who is responsible for generating good data? Can the designs be improved to increase data integrity?

If this is a problem with GC, I flashed back to a quote from Prof. Colin Pool cited by Dr. Luong in his opening statement: “For any problem that can be solved by gas chromatography, I see no need to use any other technique but gas chromatography. For those that cannot, that is unfortunate, but this is the basic reason why we have, and need, a family of separations techniques.”

The next-generation GCs should address these concerns to improve performance and reduce the cost to society, because we need reliable numbers, quickly and economically.

Reference

  1. Majors, R.E. LC·GC Int. 1989, 2(12), 13–15.

Dr. Stevenson is Editor of Separation Science, American Laboratory/Labcompare; e-mail: rlsteven@comcast.net. Dr. Gras is Associate Analytical Manager, Dow Chemical Co., Fort Saskatchewan, Alberta, Canada. Dr. Lee is Professor of Chemistry, Brigham Young University, Provo, UT, U.S.A.

Comments