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Pain panel causing you pain?

11 Oct 2012

Particularly if you are using an AB Sciex’s iMethod for pain management drugs in urine, you might be noticing a shorter lifetime on your Ultra Biphenyl columns. These are challenges that we are facing and currently looking for the best solution. Since those methods in question do not contain cleanup methods such as SPE, the best approach is to provide maximum protection for the column. Here is what we suggest:

1. Check your method.

Make sure that you are centrifuging at the speed that is given. For the “Full Panel” method with hydrolysis incorporated, your speed should be 21000 g. Please note that “g” is not the same as “rpm”. Since the calculation depends on the radius of your rotor, etc., you should check your centrifuge manual or with its manufacturer to see what rpm is required to give an adequate “g” level. If you’re not sure, it’s best to shoot for higher speed, as long as you’re not exceeding the rating given for the rotor that’s being used.

Make sure that you are using an inline filter as described in the method. We sell one similar to the one shown in the method. Ours is catalog number 24993.

2. Backflush your column regularly.

Usually about once a week is reasonable, but may be needed more often if you see an increase in backpressure.

(If it makes your life easier, you can use acetonitrile in place of methanol and formic acid instead of glacial acetic acid.)

3. Add a guard column and a cap frit with 0.5 µm porosity, catalog number 25990.

I suggest using a 10 mm guard cartridge, catalog number 910950212, with Trident Direct Guard holder, catalog number 25021. Replace the cap frit with every set of injections. Replace the guard cartridge about once a week. (You shouldn’t need the inline filter described in #1 if you’re using a guard.)

4. Consider programming a “cleaning cycle”.

Use this at the end of each set of injections. Program your gradient starting at 95% aqueous, hold for 2 minutes then increase the 95% organic and hold for 2 minutes or more. Then change your gradient back to 10% aqueous and equilibrate for another 2 minutes. This should help to keep your column clean and you may not need to backflush quite as often, particularly if you are also using this in combination with a guard column.

5. Consider pre-filtering your sample with a syringe filter.

Since your sample is mostly aqueous, I’ve been suggesting one with a nylon membrane and 0.22 µm pore size, such as catalog number 23970. An alternative might be a Thomson step vial, such as catalog number 23950. A word of caution that you should check to see if the step vial works OK with your autosampler, as sometimes there are constraints associated with needle depth for injection.

6. Keep a backup column on hand.

When all else fails, replace your column. If you follow all of the precautions above, hopefully you can extend the life of your column somewhat. However, the matrix itself will eventually have an effect on the packing material in the column. The only solution for that would be to add a cleanup step in sample prep, which unfortunately may not be an option for you.

7. Consider an alternate column and/or method

If losing resolution is the issue at hand, a column with dimensions of 100 x 2.1 mm (catalog #9109512) will likely last a little big longer. You might also consider switching to our newer product, the Raptor Biphenyl.

If you need assistance with any of the above, feel free to give us a call in Tech Services.