Pitfall in the high-throughput quantification of whole blood cyclosporin A using liquid chromatography-tandem mass spectrometry

In a growing number of laboratories the technique of liquid
chromatography-tandem mass spectrometry is used for the
quantification of cyclosporin A in whole blood, employing
cyclosporin D as the internal standard. Cyclosporin A is
extensively metabolized in vivo; in liquid chromatography-tandem
mass spectrometry respective metabolites can give rise to both
parent and product ions that are isobaric with ions commonly used
for the detection of cyclosporin A and cyclosporin D, respectively.
In this article it is demonstrated that limited chromatography with
co-elution of such metabolites together with cyclosporin A and
cyclosporin D can lead to incorrect results.