By Anonymous on Monday, May 31, 2004 - 08:05 am:

Dear all,

I am new to LCMS quantification analysis, as I am trying to quantify(first time) the drugs using SRM, I face the follwing problem,

1. I got good results on Drug and Internal Standard in Mobile phase (Plain without Plasma)

2. In the case of Plasma samples (in-vitro) I got only 10-20% recovery only, HPLC results shows around 80-90% recovery...

I got a very good linearity for the plain samples upto 5 ng.

But In plasms samples, I face problem, Generally MS is sensitive than HPLC...

Is the plasma interfere the ionsation of my drug and internal standard? we have changed the method by increasing the flow rate, changing the column, increasing the run time and changing the mobile phase... Still our recovery is around 20%...

Your valuable suggestions are welcome.

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By Uwe Neue on Monday, May 31, 2004 - 11:14 am:

In MS, you often have ion suppression by coeluting compounds in the plasma sample. There was an article in the Rapid Communication in Mass Spectrometry a short time ago by Mallet and Mazzeo on the subject. This usually can be solved by doing improved sample clean-up, for example solid phase extraction instead of protein precipitation.

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By Johnson Martin Gnanamuthu on Thursday, June 3, 2004 - 09:27 pm:

I am also new to this LCMS plasma analysis
Kindly do the below mentioned:

If you are using Acetonitrile 1:1 or 1:2 , increase that more than 1:5 ( plasma:oraganic), it will give you good results.

If your method is SPE, Water with formic acid wash,then a methanol wash may give you the needed results, elute with acetonitrile or organic ( depends on your analyte interest)


Martin,
India

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By Johnson Martin Gnanamuthu on Thursday, June 3, 2004 - 09:31 pm:

Plasma protein precipitation

If you are using Acetonitrile 1:1 or 1:2 , increase that more than 1:5 ( plasma:oraganic), it will give you good results. This may remove the plasma interfereance


Regards,
Martin

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By A.Mouse on Thursday, June 3, 2004 - 11:47 pm:

If you have a problem with MS response, the problem is always ion suppression. You should look at your sample preparation method. Actually, since you are not mentioning it, are you doing any sample preparation?

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By MG on Friday, June 4, 2004 - 07:24 am:

You can also infuse your standard solution post-column with a mixing tee, then inject some solvent blanks followed by a plasma blank. Compare the chromatograms for the two. Negative peaks in your plasma blank show areas of suppression. Then you may be able to chromatographically separate the suppression from your analyte.