title: Pitfalls and prevention strategies for liquid chromatography-tandem mass spectrometry in the selected reaction-monitoring mode for drug analysis.
abstract: 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, as well as manual spectral investigation in 1 case, to perform verification and identification of interfering compounds.
  
  
  RESULTS
  We observed that false-positive results involved: a metabolite of zolpidem that might have been mistaken for lysergic acid diethylamide, benzoylecgonine mistaken for atropine, and 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% and 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.
authors.affiliation: CHU Limoges, Department of Pharmacology-Toxicology, Limoges, France.
authors.forename: François-Ludovic
authors.initials: FL
authors.lastname: Sauvage
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Gaulier
authors.forename: Gérard
authors.initials: G
authors.lastname: Lachâtre
authors.forename: Pierre
authors.initials: P
authors.lastname: Marquet
mesh_terms: D001285:Atropine / Q000737:chemistry / Q000652:urine; D002853:Chromatography, Liquid / Q000379:methods*; D002997:Clomipramine / Q000032:analysis / Q000378:metabolism; D006801:Humans; D008238:Lysergic Acid Diethylamide / Q000737:chemistry / Q000652:urine; D015394:Molecular Structure; D004364:Pharmaceutical Preparations / Q000032:analysis* / Q000737:chemistry*; D010640:Phenothiazines / Q000032:analysis / Q000378:metabolism; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D004364:Pharmaceutical Preparations; D010640:Phenothiazines; D001285:Atropine; D008238:Lysergic Acid Diethylamide; C031637:phenothiazine; D002997:Clomipramine