RIP GC?
When disruptive technology comes along, it can be hard to defend the technique under attack for some applications – even if we have embraced it for decades.
Ray Perkins |
For the first time, I find myself viewing gas chromatography as quaintly passé. It’s the same sensation I experienced when, as a Nokia mobile phone user, I picked up an iPhone for the first time. It’s the feeling you get when you find yourself staring the future in the face; it has crept upon me as I have become acquainted with selected ion flow tube mass spectrometry (SIFT-MS).
GC has served us well for more than half a century, separating mixtures of non-polar volatile organics and presenting the components to a detector as a time series for identification and measurement. Hyphenated with MS, GC does a good job, but long familiarity kept me blind to some significant faults.
When it comes to small molecules, SIFT-MS can separate and measure pretty much everything that GC can – but unlike GC, it handles polar compounds well. For example, it can analyse BTEXs, carbonyls and acid gases at the same time. In part, this is possible because introducing samples into a SIFT-MS is ridiculously simple – the instrument sucks the sample in through a hole. With GC, your sample has to navigate the GC’s injector – one of the most misunderstood, troublesome and error-prone devices known to science.
The second major issue is speed; SIFT-MS is really fast. Not “fast GC” fast (which is still slow) but “getting-the-job-done-and-dusted-in-seconds” fast. This changes things in more ways than you can imagine and leaves GC trailing behind and out of sight.
Let’s begin with method development. With SIFT-MS, the experimental feedback loop is so short you can complete method development typically in a few hours. And that means you can experiment more because it is quick and cheap to do so. The speed of SIFT-MS also opens up new possibilities that are closed to gas chromatography.
In comparison, imagine deploying SIFT-MS on the production line so that every product could be tested in real time. The feedback on pass/fail conditions is immediate, and the incremental cost of additional measurements is pretty much zero. The business can deal with problems the moment they arise and can individually certify every product they make.
Moreover, there are many chemical processes where significant changes occur at a rate that GC cannot track. GC instruments also have sample size limitations; sampling volatile compounds in air at low levels means having to take each air sample through several cycles of adsorption and desorption to reduce the volume of sample to a volume that the GC can accommodate. In contrast, SIFT-MS can sample air directly and offers pptv detection limits for many analytes. Adsorption tubes aren’t needed; instead, SIFT-MS gives a real-time continuous measurement of concentrations in air.
The final issue I have with GC is that you must obtain a standard for each compound of interest and you have to run standards to calibrate the instrument.SIFT-MS, on the other hand, measures concentrations from first principles.
In truth, the overlap between old and new technologies is never 100 percent (compact discs never fully replaced vinyl records) and GC will continue to be an important technique for many years to come. However, the rose-tinted glasses through which I used to view GC have gone forever – replaced by spectacles lightly tinged with Norwegian Blue*.
*If you don’t get it, Google it!
Ray Perkins has worked with gas chromatography his whole working life; and, in 1996, formed his own company, Anatune, which supplies instrumentation for chromatography sample preparation and automation. “Chemistry underpins just about everything that matters and in chemistry, you can only make progress if you can measure things properly. Much of what our customers need to measure is ‘only just possible’ and we help them to push the limits of what chemistry can do for us all.”
