Chromatography Forum

Please can any body explain me why petrolium ether shows 3 to 4 splited peaks on Carbowax columns

Sitaram,

Look up Petroleum Ether in Wikipedia. Carbowax sometimes does a wonderful job of separating light hydrocarbons (m/p-xylene for example.)

Best regards.

Hi

Some general info (niked from wiki and others):

Petroleum ether, also known as benzine, VM&P Naphta, Petroleum Naphta, Naptha ASTM, Petroleum Spirits, X4 or Ligroin, is a group of various volatile, highly flammable, liquid hydrocarbon mixtures used chiefly as nonpolar solvents.

Petroleum ether is obtained from petroleum refineries as the portion of the distillate which is intermediate between the lighter naphtha and the heavier kerosene. It has a specific gravity of between 0.6 and 0.8 depending on its composition.


Ligroin for example is a refined saturated hydrocarbon petroleum fraction similar to petroleum ether used mainly as a laboratory solvent. It predominantly consists of C7 through to C11 in the form of about 55% paraffins, 30% monocycloparaffins, 2% dicycloparaffins and 12% alkylbenzenes. It is nonpolar. Generally laboratory grade ligroin boils at 60 to 90 °C, but the following fractions of petroleum ether are commonly available: 30 to 40 °C, 40 to 60 °C, 60 to 80 °C, 80 to 100 °C and sometimes 100 to 120 °C. The 60 to 80 °C fraction is often used as a replacement for hexane.

So in conclusion, the number of peaks, some splitted depending on colum etc may appear depending on what composition you have bought.

This may not only be seen in GC purity tests but also in residual solvents analysis.
A collegue of mine observed the very same thing with Ligronin with a carbowax column when doing some residual solvents testing on an API.

Carbowax columns (quite polar) may not be the most suited for this kind of analysis, check with you column supplier/catalog for a better non-polar option.
If you happen to do residual solvents analysis, the DB-624 might resolve the peaks but unsure.

I use petroleum ether as an extraction solvent, and depending on the manufacturer or even the batch it can have quite different boiling points and gives different interferences. Suffice to say I am trying to switch to hexane.