Thinking Outside of the Box, Part 1: Coeluting Compounds on Purpose?

Before joining VUV Analytics, I graduated with an MPS in forensic science, adding to my BS in chemistry.  During my education, I spent considerable time – both in class and in lab – learning the ins and outs of chromatography.  Much of that time was dedicated to learning the art of method development.  If done properly, a chromatographic method gives the most bang for the buck by balancing the shortest possible run time with efficient compound separation.

While in school, I was taught that two peaks should be separated with a baseline resolution of 1.5; any higher and the run time is unnecessarily long, but too low and the compounds coelute.  In the worst-case scenario, a compound’s chromatographic peak could be absorbed into a coeluting compound’s peak, making it undetectable.  Coelutions can make chemical analysis difficult (speaking from experience), so it’s usually easier to avoid them by lengthening the run time.  Figure 1 depicts a hallmark example for gas chromatography of troublesome coeluting peaks, m- and p-Xylenes.

Figure 1. m-Xylene and p-Xylene coeluting as a single GC peak.

Since joining VUV Analytics, however, I’ve learned that the tenets of traditional chromatography don’t necessarily apply to GC-VUV.  As if in direct opposition to what I learned in class, method development using GC-VUV allows us to shorten run times and force compounds to coelute on purpose!   But wait, doesn’t that mean I’ll have to deal with the issues I just described above?  Not with the spectral deconvolution power of GC-VUV!  Within seconds, the coeluting compounds in Figure 1 can be automatically distinguished and identified as shown in Figures 2 and 3.

Figure 2. Distinction of m-Xylene and p-Xylene using VUV spectral deconvolution.

Figure 3. The VUV absorbance spectra of m-Xylene and p-Xylene are unique, which allows for their spectral deconvolution, something not possible when using mass spectrometry where their spectra are essentially identical.

The time-saving capabilities of GC-VUV have already been demonstrated.  The analysis of spark-ignition engine fuels, for example, has traditionally been performed using GC-FID with run times up to three hours long (see ASTM D6730-01).  However, using GC-VUV with ASTM D8071-17 allows the same type of analysis to be completed in under 35 minutes!

As someone who thought that long run times were just inherent to chromatography, I’ve been blown away by what GC-VUV can achieve.  I’m excited to continue exploring how GC-VUV changes our perspective on the limits of traditional chromatography!