problems w/ precipitation&extraction of hydrophilic drug

[Uwe Neue]

Neuger,

I can give you some advice on efficient SPE methods, if you want. We have done a lot of studies on this subject. I have not worked with your compound, but I can give you a set of methods that work for us in a generic way. Either in public or in private, as you wish...

[HW Mueller]

Now I am even more confused:
You say:
"it is all related to ion suppression, not a co-eluting endogenous "dirty" peak."

then later:

"sample clean up in SPE is my proposed solution...."

then:

"and to reduce the plasma matrix suppression by removing many interferences."

Inbetween the last two statements you are mentioning a change to a mobile phase that doesn´t cause suppression?

Sounds like you are saying that your suppression problem was due to remaining sample matrix + mobile phase?

[neuger]

I think there is some confusion about sample clean up in relation to the words chosen. I shouldn't be using the word interferences, anything in the plasma causing ion suppression IS an interference to me, but I didn't mean like a co-eluting peak in a chromatogram . I have followed everything at larger concentrations on a DAD and know that the ion suppression is the problem.

Poor choice in words, sorry about the confusion. I did say removing matrix suppression by removing interferences, I guess I should have said remove the matrix suppression by better clean up.

[Uwe Neue]

Hans,

I thought it is clear: he injected his analyte in a solution without plasma, possibly mobile phase. Then he injected the same concentration of analyte in made up in a blank plasma sample that had been treated with his standard sample preparation procedure. The peak with the treated plasma was about 4% of the peak in his neat solution. Hence 96% suppression.

[james little]

Excellent book on ion suppression/enhancement plus many other useful topics..

http://www.amazon.com/Using-Mass-Spectr ... 0849319633

Also, we have done some studies which are shown at

http://littledomain.com/james/files/text.pdf

plus other info at

http://users.chartertn.net/slittle/

[HW Mueller]

Ok, Uwe, the way you stated it one doesn´t even need one further word on where the suppressives are and from where they came.