Chromatography Forum

If anyone uses this type of nonbonded bis-cyanopropyl polysiloxane phase column can you tell me how many injections or the lifetime you are getting?

Thanks for your replies

What analytes are you injecting AND from what matrix do they inhere? Acidified, caustic, solvent, or dilute-n-shoot from a product formulation or environmental native matrix?

We are injecting FAMEs from biological samples (blood, plasma) methylating Fatty Acids with BF3 Methanol and extracting with Hexane (also adding Water to seperate phases).

We inject FAME's from vegetable oils and can run more than 1,000 samples on a column. I do notice that the retention times for the peaks gradually decrease as the column ages but even columns in use for more than one year still give adequate separation.

Are you salting your aqueous extraction phase adequately? Do you dry your hexane extraction before injecting? A little sloppiness (you would never commit such an offense I am sure) can damage your column.

A little carry-over of BF3 (HF) or water can do a lot of damage to a silicone phase.

Do you have oxygen in your carrier gas? Is your injection septum leaking out carrier and leaking in air into the gas stream? Cyano phases are reactive.

best wishes,

Rodney George
consultant

Thanks for the replies. We are currently getting 1000-1500 injections on our columns and was just seeing if this was the normal range for these. We are trying to increase the column life as these columns are expensive and we run 1,000 samples easily a month. We currently do not salt our aqueous phase but is something we are looking into. We do not dry our hexane layer down before injection either, we ran a test on this for a couple of months, by drying our samples down, and found that this did not make a difference in the lifetime of our columns. We use ultra high pure gas with all the necessary filters on the gas lines, so nothing we can change here. As for the injection septum issue we change our septa every 250 injections, we found that just before 300 or after 300 injections we found two peaks showing up at the end of our run and when we change the liner and septa they vanish, and we attributing those peaks to conatimation, and this is how we set our 250 injections. We are also thinking about increasing our sampling volumes as right now we are in the microlitre range and the distance from the hexane layer to aqueous is not very thick, so have to be really careful not to get any BF3 or H2O...This was my first recommendation. I look forward to the responses. Thanks Again.

If you wish to stay with a non-bonded phase but high polarity, Supleco may have an alternative (cyanopropyl polarity) phase that might be more stable than the phase you may be using today.

Some manufacturers (which will remain nameless) may have other choices that might have longer service lifetime for your application. Call around and ask R+D dept heads if they can offer any assistance.

I am also aware of a polar but bonded phase for Chromosorb W support that might also be an alternative for packed column applications. These phases may not be on the market but may be available. Many times new developments are not put on the market as no one wants to invest in the money and time in marketing them.

Of course, you can always ask for a volume discount and order columns 5 or 10 at a time.

best wishes,

Rodney George
consultant