Unique and remarkable interferences were observed when dried blood spot (DBS) sampling was used in conjunction with liquid chromatography/mass spectrometry (LC/MS) assays. In particular, chromatographic retention time shifting and chromatographic peak shape distortion were observed, along with a severe suppression of MS signal intensity. The type of DBS cards, and chromatographic conditions were investigated using the same set of test compounds to gain insight into these interferences. It was determined that a constituent of the DBS cards, primarily sodium dodecyl sulfate (SDS), was responsible for the interferences by means of an ion-pairing mechanism. SDS formed ion pairs with compounds containing basic amine groups, which resulted in increased retention on a C(18) stationary phase, peak shape distortion and ion suppression. These interferences were greatly alleviated and/or completely overcome with non-acidic mobile phases and/or DBS cards with no SDS coating. To the best of the authors' knowledge, this is the first in-depth report of interferences induced by DBS cards.
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