The Rise and Rise of Multidimensional GC

We spoke with Marco Koenen and Ed Ledford of Zoex about the rising popularity of multidimensional gas chromatography.

Multidimensional gaschromatography is a fairly newtechnique compared with those conventionally used inchromatography. Can you explain why its popularity is on the rise?

Koenen and Ledford: Multidimensional GC (MDGC) isbecoming popular with many GCanalysts because of the growingrealization that conventional one-dimensionaltechniques are not sufficientfor the analyses of even “moderately”complex mixtures (which describes mostsamples) and because of the ease ofintegration and operation of MDGCwithin existing GC systems.

Like all new technologies that comeonto the market, the uptake of MDGCcommercially over the last 15 years hasbeen dominated by GC opinion leaders and those at theforefront of GC research. MDGC technology has expanded andthe term is now recognized to include “comprehensive GC”(total transfer of analytes from primary to secondary column)and “heart-cutting” (partial transfer of analytes from primarythrough secondary column).

The versatility of multidimensional GC, together with simpleintegration into existing GC systems, today caters to all GCanalysts, from laboratory technicians to academic researchers.Moreover, legislation is driving detection limits to lowerconcentrations and economic demand for higher informationthroughput is also contributing to the growing popularity of MDGC. Because analysts are regularly faced with troublesome co-eluters, activecompounds, and more complex matrices,an increasing number of GC users areturning to MDGC.

Why should MDGC be considered preferable to GC?

Koenen and Ledford: Surprisingly, MDGC is almost always usefulfor any analysis requiring separation ofmore than about 37 peaks. This is becauseof the statistics of peak overlap inconventional GC: at about 37 peaks,statistically speaking, there will be at leastone difficult coelution. At 100 separatedpeaks, the game is over. Analysts arefacing an MDGC problem and probably acomprehensive GC problem at that levelof complexity.

There are several sample types where MDGC, andparticularly comprehensive GC, currently find popularity:petroleum and refinery products, fragrance and flavorextracts, forensics and clinical toxicology (metabolomics), andenvironmental applications, which include pesticides andpersistent organic pollutants (POPS). But essentially allapplications of GC, other than simple major componentanalysis, benefit from MDGC techniques.

Analysts who perform data analysis both using MDGC andGC will see a whole range of benefits, which include up to 30times more resolving power than GC, easier methoddevelopment, higher sensitivity for low-level target analytes, more accurate peak quantification as a result of reducedpeak broadening, as well as the cost and time-savingbenefits of performing one run versus multiple separateruns, often on different instruments, with different columns,and by different methods. Overall, the method developmentburden is greatly reduced.

What are the principle challenges in MDGC?

Koenen and Ledford: The key challenges in multidimensional GC are (1) transfer ofsample from the first column to the second column (switchingor modulation), (2) achieving adequate resolution for a givenapplication (method development), and (3) analyzingmultidimensional data, which requires powerful software.

Modern comprehensive GC and heart-cutting applicationstransfer sample from the first column to the second column atprogrammed times with excellent repeatability. Over the years,a whole range of flow switching and modulation devices havebeen developed and made commercially available, includingheated sweepers, cryofocused modulators, diaphragm valve-switching,and Deans-switching devices — each of which hasfound use in particular applications.

What specific MDGC technologies and techniques areavailable and what benefits do they offer the user?

Koenen and Ledford:

Dean switching enables control of flow between twodetectors to perform heart-cutting and offers additionalselectivity for trace-level analyses in complex matrices. Deanswitching uses pneumatic control as opposed to cryogenicthermal-based modulation. A purged column effluent splitteralso permits transfer of effluent to multiple detectors.

MDGC provides a simple strategy for sample enrichment.By pre-concentrating trace components in a packed column,then heart-cutting enriched trace components onto the second column, select trace components can be subjected tohigh-resolution chromatographic analysis.

What do you think is the future for MDGC?

Koenen and Ledford: MDGC will continue to expand. The word “multi” will becomeincreasingly important, because two-dimensional analysis willnot be the only way forward. Flow direction and control willpush analysis in new directions. More injection and samplepreparation techniques will be integrated into effective“higher dimensional” techniques, which will simplifymany analyses.

The key trends will be continued focus on resolution; theaims being compound class analysis, target analysis, and insome instances total analysis in key environmental,petrochemical, forensics and fragrances, food, and flavorapplications. We will also see MDGC increasingly integratedinto existing instrumentation for faster, more convenientanalysis of ever more challenging samples.

A key trend will be to replace multi-instrument methodswith single-run MDGC. MDGC is already solving everyday GCanalytical problems such as troublesome co-eluters, activecompounds and trace analytes etc. In the future, there will be ageneral shift towards MDGC techniques. In short, MDGC isthe future.

Marco Koenen is director of Zoex Europe BV. He specializes inproviding multidimensional solutions to the analytical andprocess science market. He is a graduate in biochemistry andhas worked in the industry for over 15 years.

Ed Ledfordis president of Zoex Inc.