Chromatography Forum

Hi
Im currently performing an LCMS for chloroquine and quinine in plasma. My peaks in standard solution has come out quite nicely on the lcmsms.

however after extraction from plasma only the internal standard can be identified. chloroquine and quinine has disappeared.

my plasma extraction involves adding 200ul of spiked plasma and 400ul of IS in methanol. this is then added with a buffer solution of ammformate:methanol ph4.

ive tried extracting the chlroquine and quinine with ACN but the peaks cant be detected.

i was hoping to get some advise on this. Thanks!!

You are apparently dealing with a rather bad case of ion suppression. If this is the case, you will need to work out a better sample preparation procedure, such as solid-phase extraction. I can help, if you want to go this path.

Hi! Yes please that would be great. is it possible to perform a different type of liquid preparation though. Why does the ion suppression occur in plasma samples?

Thanks!

I am recommending solid-phase extraction instead of liquid-liquid extraction. You get more predictable and better results.

Dilute your plasma sample 1:1 with a suitable internal standard and phosphate buffer pH 7.

Load this sample onto an Oasis WCX cartridge that has been activated with methanol and water.

Wash the cartridge with the adsorbed sample with 10% methanol, 90% phosphate buffer.

Wash the cartridge with the adsorbed sample with methanol.

Elute the analytes with methanol acidified with HCl or TFA and some small amount of water (<10%).

Quantities depend on the device that you are using and this in turn depends on the amount of sample that is available for analysis. Look at the Waters webside for a suitable device.

Thanks! great help. i shall give this a go.