Florisil

[WK]

Hi All,
I am interested in the reasons for clean-up prior to GC-ECD with Florisil?
Does anyone use this and why? Most of my samples would be essential oils or essential oils in hexane.
Best Regards and Happy Weekends
WK

[Steve Reimer]

Florisil cleanup (and fractionation) helps to confirm the ID of a compound if using a fractionation step, but is normally used to eliminate interferences from the matrix. ECDs are prone to both positive interferences, from other electronegative compounds in the same retention window, and negative interferences from signal supression caused by hydrocarbons. Heavy oils will also cause retention time shifts that may make confirmation of identity difficult.
Getting rid of matrix interferences will make for a much happier analyst! The cartridge type are quick, easy and inexpensive.

[WK]

Steve,
Thanks for the reply.
Do you imply that the Florisil works by taking out hydrocarbons and leaving the polar and electronegative compounds in the eluent?
WK

[skunked_once]

WK,

Florisil is a polar normal-phase chromatography packing that has been used for years for sample cleanup, particularly for removing fats and oils. As with any other chromatography application, the retention or elution of impurities and compounds of interest is controlled by adjusting the polarity of the eluting solvent. It's been several years since I used it but I remember that the Florisil should be activated in an oven at 110 C for 24 hours to remove moisture. It can be used in that form or can be selectively deactivated by adding an exact amount of water (usually in the 1-10% range) and mixing overnight. A literature search should yield many references. Also check vendors that sell Florisil for application bulletins.

[KC]

You sure you are not talking about alumina? I have used both many times and have never heard of activating florisil. Definately something done with alumina though.

[chhubert]

Alumina and florisil (or silica gel) are all normal phase media used for cleanup of hydrocarbons from polar compounds such as pesticides, PAHs, PCBs etc. To my understanding, silica gel is the weakest amongst three, then alumina, and the strongest affinity for florisil. Notwithstanding, different phases have their own selectivity, says alumina has particular affinity towards aromatic ring compounds. Adding water to this phase can deactivate it or reduce the affinity of polar compounds and thus make it more easily to be eluted by less polar organic solvents.

[skunked_once]

KC,

Alumina is deactivated to grade I, II, III, IV, V, etc. by addition of an exact amount of water as you remember. Florisil is often used as is, without activation but the Florisil can vary depending on the source so best results are obtained by deactivation by heating prior to use. Some applications may require deactivation by addition of a specific amount of water. Thanks chhubert, for your additional details.