Light Compound Analysis with LGI-GC-VUV

With ASTM D8267 for jet fuel, ASTM D8071 for gasoline, and a diesel method in development, VUV Analyzer™ for Fuels has shown itself to be a versatile platform for fuel analysis. 

These methods offer effective results with spectral confirmation, and their analysis times are more efficient than conventional methods. These techniques do not include compounds in the C1-C3 range that are very light as they volatilize too quickly under standard GC injection conditions. 

As small molecules have the most unique and interesting vacuum ultraviolet range spectra, VUV Analytics has been discovering methods of investigating these samples in the laboratory.

There are multiple choices for the analysis of gaseous samples on a GC, but gas injection into a GC frequently generates broad peaks which can result in substandard chromatography. 

Pressurizing these compounds into liquids is an alternative, known under the term liquefied petroleum gas (LPG). The liquid sample can then be injected utilizing a liquefied gas injector (LGI)

When the sample is injected in liquid form, it offers resolved, sharp chromatographic peaks. This makes it simpler to select compounds at small concentrations from significantly larger peaks. 

Even if the sample is made of permanent gases which are unable to be liquefied, the chromatography is still enhanced by the pressurized injection performed by the LGI.

An LGI system was recently configured in the VUV laboratory. The results have been promising. Figure 1 provides an example of a propane/propylene sample analyzed using a VGA-100. 

Analysis of a propane/propylene sample.

Figure 1. Analysis of a propane/propylene sample. The large propane and propylene peaks are clearly visible, while smaller peaks are separated and easily identifiable. The additional separation allows us to distinguish compounds in small amounts, such as 1,3-butadiene and methyl acetylene, in a mixture containing primarily propane and propylene. Image Credit: VUV Analytics

The volatile compounds are easy to observe and well-separated. These would usually be hidden in a conventional GC liquid injection. This enables the user to take advantage of the highly distinct spectra for the identification of compounds. 

Figure 2 demonstrates a selection of the exclusive spectra acquired from these small molecules, which frequently have sharp characteristics that are distinguishable even at trace levels.

Spectra of compounds in the propane/propylene sample.

Figure 2. Spectra of compounds in the propane/propylene sample. Small molecules tend to have very distinct spectra containing sharp features that are easily recognizable and very useful for compound identification, even at small concentrations. Image Credit: VUV Analytics

Compared to the conventional FID detector, VUV technology has an advantage in that it offers spectral confirmation of compound identifications similar to its other methods. 

VUV spectroscopy can also deconvolve coelutions that may still be present, making quantitation easier and enhancing the accuracy of results. 

The combination of GC-VUV with an LGI system may lead to the discovery of new techniques, for example a VUV-version of ASTM D2163. LGI-GC-VUV applications in the future are highly anticipated.


  • Produced from materials originally authored by Ryan Schonert from VUV Analytics.

This information has been sourced, reviewed and adapted from materials provided by VUV Analytics.

For more information on this source, please visit VUV Analytics.


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