LRI differences between theory and practices

[Bill040689]

I am dealing with a problem that some of my compounds have different LRI with the ones stated in the literature. I have compared them with the ones with the same column type. For example, in my trial, LRI of nonanal is 1386 while the literature says 1416 (the difference is 30). I want to ask, how far the difference which can be still tolerated? It also surprised me that apparently, some journals also have different LRI for the same compound with far difference, for example: in journal A, LRI of octanoic acid is 2241, while in journal B, the LRI is 2060 (the difference is 181).

[Peter Apps]

The major source of differences between literature retention indices is that nominally similar phases from different manufacturers are actually rather different. This is especially true for the polar phases. What column are you using ?

Peter

[Bill040689]

Thank you so much for your kind answer, Mr. Peter. I'm using HP-Innowax with inner diameter: 0.25 mm, length: 60 m, width: 0.25 μm. And yes, it is polar. Can you please enlighten me why it is especially true for the polar phases?

[Peter Apps]

Presumably because there are differences in the recipes that different manufacturers use to deactivate, coat and cross-link the columns. The non-polar silicone phases are much more unifrm batch to batch than the waxes or the highly substituted polar phases.

Peter

[sepscientologist]

Also, nonpolar compounds separate compounds primarily by volatility or boiling point and the indices are defined by comparisons
to hydrocarbons, ie, only van der waals types of forces. Polar phases are used for enhanced selectivity of particular functional
groups and so, by design, try to move classes of compounds away from the predicted retention index.

[Bill040689]

Thank you so much, gentlemen. I am not trying to be rude, but if you have a link to the literature about what you explained to me, I will appreciate it so much if you are willing to give it to me since I am working on this for my thesis so I need citations. Good day. =]