selection appropriate IS for LC-MS/MS method

[Ruth]

Dear forummembers,

I am developping a LC-MS/MS method for about ten compounds. For 3 compounds, I have deuterated IS available. I would like to use these 3 IS also for the other compounds. Which criteria determine which IS for which compound?

I was thinking about:
* retention time
* structure (however, no obvious similarities can be found between the IS and the compounds)
* behaviour during extraction and analysis (thus RE and ME)

All advice is very welcome!

Thanks!

Ruth

[Uwe Neue]

I have used internal standards of different structure for a long time. The key point is that their behaviour in the extraction procedure is identical, which you can check independently without the matrix, and that there is no difference in ion suppression in the MS due to matrix effects, which again can be checked following the usual procedures of spiking a blank matrix with both analyte and internal standard and then executing the extraction procedure and the analysis as usual. The first problem is a question of the quality of the extraction procedure. The second is primarily the same issue, but if the extraction procedure is not perfect, it require some manipulation of the LC/MS analysis as well.