Matrix Effects in LSMS Analysis of Plasma Samples

[james little]

I have spent a lot of time trying to minimize the effects of matrix effects in the analysis of basic drugs in plasma. The major matrix interferences in samples analyzed by protein precipitation are phospholipids and lysophospholipids

I developed a method to employ one ion in MRM LCMS analyses that detects all the high-level lysophospolipids and phospholipids. I then used these to minimize the analysis time while still separating the basic drugs from these lipids. The basic useful parameters were flow, solvent composition, and temperature.

I also evaluated the effects on accuracy, precision, peak shape, retention time, column backpressure, etc when these lipids were not eluted from the column.

I was surprise to find that the signal for these lipids become "steady-state" in concentration. Also they began to elute with the analyte after many injections. After they became steady-state, and the analyses were not severely compromised.

I would be interested in others observations/comments:

see

ASMS Poster: "Simple Method to Monitor Lysophospholipids and Phospholipids During LC-MS Method Development via In-Source CID"

see

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

Top subject.

[MG]

Nice work, James!

[james little]

Thanks for the feedback.

Do you do plasma analyses?

[MG]

Yes, and I've also been plagued by the problem of lipids accumulating on the column from plasma extracts, and causing the apparent response of the MS to drift. Another neat ASMS poster on the subject of the phospholipids was WP 210, where the authors showed a table of various liquid-liquid extraction systems and how much phospholipid was extracted versus their small-molecule drug analyte.

[Kostas Petritis]

Next time, all the people from this forum that will go to ASMS (next year will be in Seattle) must meet together and have a drink.

It is always good to put a face to the names/alias.

[MG]

Kostas, I stopped by your poster and was going to introduce myself, but you were engaged in conversation with someone else. So I planned to stop back by in 15 min or so, but apparently was distracted by something else! I did request a reprint of your poster, though.

[Kostas Petritis]

Oups bummer,

I'll go through the business cards back home and send you the poster reprint (otherwise it will take a while). Is MG your initials?

[MG]

Yes, those are my initials. Thanks!

[HW Mueller]

I described a steady state "dirt" emanation in 1996 (J Chrom B, 678, 137, 1996; p. 147, top paragraph of left column). This was observed with UV detection, the maxima where at 280nm, sometimes at 230nm, or both. MS was not readily available and not checked. It should be noted that this appeared in the third step of three step analyses (commonly called three dimensional).
I have since taken this to be a given fact and am assuming that it is a problem that approaches infinity in the number of causes.