n-Alkane retention time has a clear cut boiling point relation for SimDist and the Kovats index is interpolated n-alkane carbon number times 100. In SimDist and Kovats analyses, n-alkanes must be measured along with the analysis of the sample. Not any more ! When n-alkanes are lost, input of the GC method and realistic film thickness & gas velocity can predict the peaks with great precision. StillPeaks Virtual GC precision can be Kovats index ±1 precision or SimDist ±1°F

PT diagram Methane to nC100 to predict n-Alkanes

Virtual GC: PT diagrams of Methane to nC100 by API 44 

Virtual GC: Solubility in DimethylSilicone

Virtual GC is a fugacity model of temperature programmed capillary GC that predicts CH4 to n-C100 chromatograms on Methyl-Phenyl-Silicone capillary columns. Retention time is predicted from Giddings peak move and fugacity LG equilibrium based on API44 vapor pressure and polymer solubility. Peak width is predicted from Golay zone dispersion, Chapman-Enskog gas diffusion and Stokes-Einstein liquid diffusion.

Prediction of CH4 to nC16 for Detailed Hydrocarbon Analysis (ASTM D 6730)

Today GC is so repeatable that n-Alkanes from earlier measurement can be used to identify peaks in a sample without n-Alkanes. Run a sequence of samples including an n-Alkane standard and you are ready to calculate Kovats index. No n-Alkanes measured in your sequence? Use Virtual GC calculated times based on n-Alkane Boiling Point and Solubility in crosslinked polymers of Phenyl-Methyl-Silicone. Tweak times with column wear and gas velocity to get 1-2 index units precision. 

Predict n-Alkanes for SimDist (ASTM D 2887)

SimDist calibrates the time axis with n-Alkane boiling points. Normal operation involves a sequence with

  1. a blank,
  2. a n-Alkane standard and
  3. the samples.

Virtual GC saves time measuring the n-Alkane standard.

SimDist chromatogram Initial Boiling Point and Final Boiling Point can be obtained.

Run-to-Run stability with Ultra Thin Column Coatings

Thin films have a limit (see Poly(dimethylsiloxane) ALEX C. M. KUO). Ultra thin films are amenable to thermal degradation. StillPeaks Virtual GC calculates chromatograms on films down to 2 nm (0.002µm).

When coatings are so thin, run to run stability only allows the use of n-Alkanes present in the sample. One can see the heavy n-Alkanes lose retention time run after run…

StillPeaks Virtual GC calculates the missing n-Alkanes, making ultra thin film HiTemp SimDist possible!

Interested?

Predict n-Alkane chromatograms with Virtual GC!  Download the software and get a free of charge trial license.