FAQs

Q.

My thermal desorption peak is split in two. I'm running protein crashed samples from human plasma for drug quantitation (1:1 volume with acetonitrile). What's happening ?

A.

Split thermal desorption peak can be observed when there is too much material (mainly non-volatile matrix constituents) into a well.  This phenomenon can be observe with any matrix.  To overcome this problem, you should dilute your final extract.  For plasma, the recommended volume ratio when performing a protein crashed is 1:4.

If you are performing a liquid-liquid extraction or a solid phase extraction (SPE) and you are observing split thermal desorption peak, then reduce the volume of your starting material or dilute the final extract. You can also increase the volume of the washing solution to clean up your sample.  In most case, it should resolve your problem.

Q.

During CYP inhibition analysis of acetaminophen in the presence of phenacetin in HLM, I do observe acetaminophen signal in a blank sample.  Where that signal is coming from ?

A.

During the (+) APCI process, a small fraction of phenacetin ( MW 179.216 g mol^-1) is converted in acetaminophen (MW 151.169 g mol^-1) leading to a cross-contribution signal.  To overcome this problem acetaminophen should be monitored in (-)APCI where this conversion is 10-times less.

Q.

I only used half of the wells contained in a LazWell plate, can I store the plate to use the empty wells later ?

A.

LazWell plate can be store into the delivery plastic bag to avoid dust deposition.  Moreover, dry sample can also be store up to several days.  In such case, the compound stability should have been evaluated especially for light and/or oxygen sensitive compounds.