Received on February 23, 2008
Accepted on June 20, 2008

Drug Monitoring and Toxicology

Pitfalls and Prevention Strategies for Liquid Chromatography–Tandem Mass Spectrometry in the Selected Reaction Monitoring Mode for Drug Analysis

¹ CHU Limoges, Department of Pharmacology-Toxicology, France, and INSERM U850, Limoges, France
² CHU Limoges, Department of Pharmacology-Toxicology, France
³ CHU Limoges, Department of Pharmacology-Toxicology, France, and Universite de Limoges, Faculty of Pharmacy, Laboratory of Toxicology, Limoges, France

^* To whom correspondence should be addressed. E-mail: pierre.marquet{at}unilim.fr.

BACKGROUND: We observed cases of false-positive results with the use of liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Different LC-MS/MS techniques that use the selected reaction–monitoring mode, routinely employed for the analysis and quantification of drugs and toxic compounds in biological matrices, were involved in the false-positive and potentially false-positive results obtained. We sought to analyze the causes of and solutions to this problem.

METHODS: We used a previously reported LC-MS/MS general unknown screening method to perform verification and identification of interfering compounds.

RESULTS: We observed that the cases involving false-positive results involved a metabolite of zolpidem that might have been mistaken for lysergic acid diethylamide, a benzoylecgonine that might have been mistaken for atropine or clomipramine, and 3 phenothiazines that share several common ion transitions.

CONCLUSIONS: To prevent problems such as those we experienced, we recommend the use of stable-isotope internal standards when possible, relative retention times, 2 transitions or more per compound when possible, and acceptable relative abundance ratios between transitions, with an experience-based tolerance of ±15% for transitions with a relative abundance >10%, with an extension to ±25% for transitions <10% when the concentration is at the limit of quantification. A powerful general unknown screening procedure can help to confirm suspected interferences. Our results indicate that the specificity of screening procedures is questionable for LC-MS/MS analyses performed in the selected reaction–monitoring mode and involving a large number of compounds with only 1 transition per compound.