CTC autosampler carry-over

[konkous]

I'm currently developing a LC/MS/MS method for the quantitative determination of donepezil in human plasma. I'm using a CTC autosampler which seems to cause extensive carry-over with a signal almost equal to my first calibrator's. I've tried using multiple washing steps of the needle and the valve with different solvents (0.1% formic, MeOH-water, etc.) but the problem is very persistent. Could anybody help me? Thank you all in advance..

[fishin' addict]

C-O is frustrating! What type of extraction and MS are you using? Initially, my response to the problem is to simply recommend changing the syringe? We have this problem from time to time with the CTC and usually we find that its related to the teflon syringe plunger wearing out. If that doesn't fix it check your plumbing for poor connections and then finally check your valve for etching. Hope this info. is of some use.

Happy Hunting

[james little]

I had heard there is an attachment for the CTC autosampler that allows the syringe to be washed more efficiently. Never seen one, but someone said it had a fitting on the top of the syringe that flushed the syringe instead of just the normal flushing with plunger.

We use a mixture of 1:1:1:1 methanol:water:acetonitrile:isopropanol containing 1% formic acid as the strong wash and then something similar to starting gradient mix for weak syring wash. Someone in Waters Demo Lab suggested the former mix, they refer to as "Draino".

[konkous]

C-O is frustrating! What type of extraction and MS are you using? Initially, my response to the problem is to simply recommend changing the syringe? We have this problem from time to time with the CTC and usually we find that its related to the teflon syringe plunger wearing out. If that doesn't fix it check your plumbing for poor connections and then finally check your valve for etching. Hope this info. is of some use.

Happy Hunting

Thank you very much for the tip. I'm using LLE with ethyl acetate and a API 3000 tandem mass spectrometer.

[konkous]

I had heard there is an attachment for the CTC autosampler that allows the syringe to be washed more efficiently. Never seen one, but someone said it had a fitting on the top of the syringe that flushed the syringe instead of just the normal flushing with plunger.

We use a mixture of 1:1:1:1 methanol:water:acetonitrile:isopropanol containing 1% formic acid as the strong wash and then something similar to starting gradient mix for weak syring wash. Someone in Waters Demo Lab suggested the former mix, they refer to as "Draino".

Thanks for all the help. I'll follow your advice. I hope it works.