Poor Recoverability From SPE

[handlovic]

Hi All,

I am trying to use SPE to concentrate river water (4L) to a high enough concentration that I can quantitate pharmaceuticals using GC-MS. The drugs I am looking at are estrogenic hormones (E1, EE2, E2, E3). However, before I can go out to get samples I am trying to verify my SPE-GC-MS method, and am having trouble with recovering my analyte.

To do this I am spiking ultra-pure water with one estrogen (E2) as a test at the concentration of 500ng/L. After SPE extraction my GC-MS is telling me that I only have about 35% of that. To make sure the GC-MS method worked, I tested the stock today and got the correct value.

Here is how I am doing the SPE:
Cartridge: C18, 0.5g, 3mL
Pretreatment: MeOH (4mL), EtOAc (4mL), and H20 (4mL)
Flow: ~7.5mL/minute using a Vaccum Manifold
Elution: MeOH (12mL)
Drying: Vaccufuge (7.5 hrs, 45 Deg C)
Reconstitution: Pyridine (1mL)

Thank you,
Troy

[James_Ball]

You may want to reference this EPA method

https://www.organomation.com/sites/defa ... %20539.pdf

It is used for finished drinking water, 1L extraction but using LCMSMS, so you may need a different final solvent.

As for your current procedure, maybe use Ethyl Acetate first, then Methanol in the wash steps since Methanol is more soluble in water. You could have some Ethyl Acetate remaining in the sorbent keeping the sample from making good contact. For pesticides we wash with Ethyl Acetate, then Methanol, then DI water before introducing the sample.

[Steve Reimer]

If you spike 12 mL of methanol and take it through just the drying and reconstitution steps do you get ~100% recovery?
If you stack a 2nd cartridge under the first and elute them separately do you get any of your target in the 2nd cartridge?
Don't be afraid to try different wash steps either solvents or their order.