Abstract
An LC-MS/MS urine confirmation assay was developed using a "dilute and shoot" sample preparation method that was subject to interference arising from gabapentin column overload in approximately 4% of patient samples, leading to interference in amphetamine analysis. The initial analysis method used dilute and shoot sample preparation followed by LC-MS/MS analysis. The improved assay used solid-phase extraction sample preparation followed by LC-MS/MS analysis. The improved assay using solid-phase extraction and alternative chromatographic conditions resolved the gabapentin interference in amphetamine analysis. This experience illustrates the importance of thorough knowledge of likely comedications in a patient population and these drugs' elimination mechanisms. Laboratorians should be aware of the phenomenon of mass effect LC-MS/MS interference, in addition to the more common LC-MS/MS interferences caused by matrix effects and isobaric compounds.
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