Switching from an analogous to a stable isotopically labeled internal standard for the LC‐MS/MS quantitation of the novel anticancer drug Kahalalide F significantly improves assay performance

Abstract
The importance of a stable isotopically labeled (SIL) internal standard for the quantitative LC‐MS/MS assay for Kahalalide F in human plasma is highlighted. Similar results can be expected for other LC‐MS/MS assays. Therefore, we emphasize the need for an SIL internal standard for accurate and precise LC‐MS/MS assays of drugs in biological matrices. Copyright © 2004 John Wiley & Sons, Ltd.