Technology Forum: Gas Chromatography-Mass Spectroscopy (GC-MS)

This month, Chromatography Online's Technology Forum focuses on the topic of Gas Chromatography (GC). Joining us for this discussion is Sky Countryman, GC Product Manager at Phenomenex; Gary Harland, Tandem Quadrupole MS Product Manager at Waters; a Team of Experts from Thermo Fisher Scientific; and Tom Gluodenis and Terry L. Sheehan from Agilent Technologies Life Sciences & Chemical Analysis Group.

Describe the strides that GC–MS has helped to make in the fields of airport security/homeland security. What improvements can be made to improve run time and increase detection?

Countryman: GC–MS is potentially very useful in airport security as a way to quickly identify volatile compounds that can alert security officers to the presence of explosives or chemical warfare agents. Having a very sensitive and selectivity detection system such as GC–MS could help better detect a wider range of potential threats - including chemicals commonly used in the manufacturing of explosives. The main challenges are sample introduction, miniaturization, and the need for skilled operators.

Harland: The diverse nature of threats to security, such as chemical and biological, places demands on resources that mean screening systems require capabilities to detect multiple threats. The ability to identify, and importantly, to confirm, security risks first time with confidence will lead to reduction of false positives and avoid unnecessary escalation of issues. High performance GC–MS systems are maturing to deliver these capabilities, but the challenge going forward is to make the advanced technologies available for general use at point of contact in the field, in order to meet the speed and detection expectations of users of in situ technologies such as IMS.

Thermo: In the fields of airport security and homeland security, the need for speed is critical, but even more important is the need to have accurate identifications with a minimal number of false positives. Because positive results are disruptive in terms of time, money, and overall traveler or civilian comfort, it is critical that devices used for screening and confirming threats be both sensitive and fast, with high accuracy. Historically, sensor arrays fit the bill in terms of speed and sensitivity; however, they are susceptible to false positives. Mass spectrometry offers vast reductions in false positives when used as a confirmatory technique for frontline sensors. Being able to perform high speed gas chromatography with accurate detection to reduce false positives is critical for real-time threat monitoring.

Gluodenis: Analytical instrumentation plays an important role in supporting several distinct mission critical tasks associated with homeland security: pre-incident monitoring/screening, incident response and recovery, consequence management and mitigation, and attribution and forensics.

Pre-incident monitoring/screening. A critical priority that has been named in the U.S. National Strategy is the development of an intelligence and warning system that can detect terrorist activity before it manifests itself in an attack. GC–MS is well-suited to general screening for very large numbers of targets in widely varying and complex matrices.

Incident response and recovery. Ongoing enhancements in detection power, coupled with its inherent confirmatory nature, makes GC–MS broadly applicable for the rapid identification and measurement of broad classes of hazardous chemicals. 
Consequence management and mitigation. GC–MS instrumentation provides sensitive, confirmatory chemical-detection systems for assessing the progress of ongoing decontamination operations and confirming complete remediation of the incident site.

Attribution and forensics. A wide array of analytical tools including GC–MS have long been used in assisting federal, state and local law enforcement in their efforts.

GC–MS has become a valuable tool in sports doping testing. What are the strengths and limitations of this form of testing as compared to others?

Countryman: GC–MS is the "gold standard" for anti-doping testing. The historical usage means the analysis technique is widely understood and accepted by the legal system. The problem with so called designer drugs is that they are made to fool the current testing methodologies. As the criminals adapt, we must develop alternate extraction and analysis methodologies that give us more information about these new classes of compounds.

Harland: GC–MS remains a popular technique in sports doping due to the sensitivity and selectivity of the technique in a complex and challenging field. Historically, the confirmatory nature of mass spectrometry has allowed the technique to dominate adopted methodologies. The extensive sample preparation required to make the increasingly wide range of compounds amenable to GC–MS means that some methods are now superseded by advances in LC–MS technology, for example Ultra Performance LC which is revolutionising LC separations and the advances in LC–MS-MS technology over recent years.

Thermo: GC–MS as a technique incorporates gas chromatography for separation, and a range of mass spectrometry options for detection and quantification of compounds. From unit-mass resolution single quadrupole mass spectrometers through high-resolution magnetic sector double focusing instruments, there are a range of options available for sports doping testing. Typically, lower resolution, and lower-cost instruments provide the first line of screening, and some confirmatory testing, for drugs of abuse and doping. However, to accurately discern between endogenous hormones and synthetic administration indicative of doping, high resolution, isotope ratio GC–MS systems are required. In fact, the recent arbitration ruling of doping against cyclist Floyd Landis hinged upon this determinative method of identifying the presence of synthetic testosterone. As a confirmatory technique, isotope ratio mass spectrometry (GC-IRMS) offers incredible resolving power. Yet its limitations are the cost and complexity of the instrumentation. Labeled standards and expertise of analysts combine to make this technique more expensive.

Gluodenis: Sports doping is a chromatography application that places some special demands upon the instruments carrying out the work. Equipment must, above all, be reliable, because downtime is unacceptable, especially in a major event. The instrument must be able to process large numbers of samples in the lab with a rapid turnaround time – those being tested have a right to a prompt result. Day-to-day reproducibility is also crucial, particularly where confirmatory analyses are concerned, to assure confidence, as results may well be challenged.  For most, LC/GC coupled with some form of mass spec is the preferred technology for doping testing.

Based on questions 1 and 2, what industry do you see GC–MS breaking into in the future and what advances can we expect to see?

Countryman: I see the biggest potential for GC–MS in the pharmaceutical and food testing because these industries have not historically relied on GC–MS. But, as supply chains move internationally the quality of the raw materials will come under increasing scrutiny. The Melamine scare was just one example of how this problem can happen. In that case, GC–MS was the analysis technique first used to identify Melamine.

In order for this to happen, there will be an increasing need for highly specific GC–MS reference libraries and software that will make the identification in complex mixtures easy. Systems will also need to be more sensitive and there will most likely be increased need for GC–MS-MS capabilities to identify contaminants within complex mixtures.

Harland: While we have observed significant growth in environmental and food safety applications in recent years, we are seeing emerging demands for GC–MS techniques applied to food authenticity testing, metabolite profiling and clinical biomarker analysis (e.g. breath gas).

Thermo: Recent news articles over the summer regarding contamination of pet and people food items point to a growing need to ensure the safety of packaged foods and beverages across the global food market. GC–MS can address the needs to monitor food safety in a manner that provides both speed and certainty. Because delays due to testing can cause entire shipments of food to spoil during the hold time, it is critical to have analytical techniques in place that can provide cheap, easy, and reliable results in the shortest time possible. Sample preparation methods such as the QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) method have been developed to shorten sample prep times, with less waste and lower use of toxic solvents and chemicals. Samples prepared using the QuEChERS method present challenges to instrumentation, challenges which require robust performance over extended periods of time. A single quadrupole GC–MS system can be paired with the QuEChERS method to provide fast confirmations of pesticides and other contaminants in food, providing speed and certainty for this critical area.

Sheehan:LC–MS is most often discussed as a replacement for GC–MS. The two methodologies have a number of similar fundamental strengths that are highly desirable for most analytical workflows:

And relative to LC–MS, GC–MS has several specific strengths.

But GC–MS is also faced with several limiting factors. First, it requires a compound that can be vaporized in the GC injector without significant degradation (also no degradation during the separation). Second, it requires a sample matrix that is volatile or does not leave large, ‘active’ deposits in the injector or column inlet that degrade the performance of subsequent injections.

The two main strengths of LC–MS relative to GC–MS are that the injection technique is easily adapted to large volume injections for trace analysis and not prone to ‘activity’ issues, and applications include many GC-compatible compounds and many more non-volatile (or thermally degraded) compounds that are not GC-compatible.

But, LC–MS has weaknesses compared to GC–MS as well.
  
With this background information in mind, LC–MS represents a more direct challenge to GC–MS than immuno-assays. In general terms, the balance between GC–MS and LC–MS can be described as the following. GC–MS is the method of choice if (a) the compound is amenable to GC vaporization without laborious, error-prone derivatization, and (b) the sample matrix is amenable to robust GC injections without excessive sample preparation.

Is there any practical application area where you can see GC–MS being replaced? For what reasons?

Countryman: In most industries, GC–MS testing will not decrease - it just won't increase. For instance, the forensic toxicology market in the USA is heavily exploring LC–MS-MS as an alternative for drugs of abuse testing. However this is primarily in new matrices such as hair and saliva. The traditional analysis from urine is likely to stay with GC–MS because of its legal precedent as the "gold standard" for drugs of abuse confirmation.

Similar things are happening in the environmental testing market. GC and GC–MS have been used to look for persistent organic pollutants (POPs) for so long, that we have pretty much seen everything that is volatile enough to be analyzed by GC. Now we need to know what else we have been missing like Perfluorinated Surfactants.

As with the toxicology industry, this doesn't mean that GC–MS will go away, it just means many of the new methods are going to utilize LC–MS-MS or some other hyphenated technique. Either way as the cost of MS comes down, MS is going to become increasingly popular detection method for any number of techniques.

Harland: Yes. While GC–MS continues to be the technique of choice for many analyses, the more rapid development of alternative techniques is being to meet demands for reduced sample preparation, improvements in separation capability, and multi-functional analyses (e.g. rapid polarity switching and multi-mode ionisation for improved productivity) for rapid screening and confirmation applies to a wide range of applications. There is also a possibility of direct ionisation techniques such as DESI and DART beginning to offer alternative sampling capabilities which may offer benefits in speed and ease-of-use.

Thermo: GC–MS remains a method of choice for the screening and control of individual target compounds, due to an increased number of international directives and initiatives mandating the use of GC–MS. It is the “gold standard” for confirmations in many application areas, and therefore provides a high degree of certainty. However, there are practical limitations to both gas chromatography and mass spectrometers that can be overcome by applying alternate separation and detection techniques. For example, in toxicology, standard GC–MS analyses typically require a derivatization step as a part of sample preparation to improve chromatographic performance of certain drug classes. Liquid chromatography coupled to single quadrupole, triple quadrupole, or ion trap types of mass spectrometers can be applied to these types of samples, which reduces or even eliminates the need to derivatize samples prior to analysis. As LC–MS as become less expensive and easier to perform, GC–MS may be replaced by liquid chromatography techniques in this type of application in order to improve productivity and decrease sample preparation time and costs. However, in most cases, LC can complement GC, augmenting a laboratories’ capabilities by expanding the list of target compounds that can be analyzed.

Sheehan: The compounds included in commercial libraries such as NIST, Wiley, and PMW nicely define the application domain of GC–MS. Although there is always the possibility of new compounds within the volatility requirements of GC technology, the opportunity for new GC–MS compounds is not comparable to the vast array of possible bio-analytes facing LC–MS users. There are, however, a number of reasons why GC–MS will continue to expand within the high-use applications (environmental, toxicology, food) and selected low-use applications (natural product research and pharma). Detection specificity, detection sensitivity, qualitative information content, separation power, ease-of-use, and cost per test (total cost including sample prep) are a few key reasons for the increased popularity and increased use of GC–MS.

As far as advances, the GC–MS is a fairly mature technology, so most advances will take shape as small increments incorporated into existing platforms.

GC–MS-MS will also provide new qualitative tools for true unknowns in developing fields such as natural product discovery. Although biotechnology holds many promises for new drug therapies based upon recombinant proteins and oligonucleotides (RNAi, siRNA), small molecules still dominate (> 75% of sales) the pharmaceutical market.