The need for chromatographic and mass resolution in liquid chromatography/tandem mass spectrometric methods used for quantitation of lactones and corresponding hydroxy acids in biological samples.
Because of the potential in-source conversion between a lactone and the corresponding hydroxy acid, it has been recognized that a liquid chromatography/tandem mass spectrometric (LC/MS/MS) method developed for quantitation of a lactone drug in the presence of its hydroxy acid metabolite (or vice versa) must incorporate chromatographic separation between the two compounds, unless in-source conversion between the two compounds has been eliminated by the appropriate selection of the LC/MS/MS parameters. We now report that chromatographic separation between a lactone and its hydroxy acid will be required under certain LC/MS/MS conditions used even in the absence of in-source conversion. This is due to the fact that the 18-mass-unit difference between a lactone and its hydroxy acid is, by coincidence, different by only one mass unit from the 17-mass-unit difference between the [M + H](+) and [M + NH(4)](+) ions of the lactone or the hydroxy acid. Thus, the [M + H](+) ion of a hydroxy acid is higher than the [M + NH(4)](+) ion of its lactone by only one mass unit. Therefore, in a method developed for quantitation of a hydroxy acid drug utilizing a selected-ion-monitoring (SRM) scheme that incorporates its [M + H](+) ion as the precursor ion, the quantitation would be inaccurate due to the interference by the contribution of the A + 1 isotope response from the [M + NH(4)](+) ion of the lactone metabolite present in the sample, unless there is a chromatographic separation between the two compounds. This is true even if Q1 is operated under a unit-mass resolution. The implication of this type of interference, arising from the presence of both the [M + H](+) and [M + NH(4)](+) ions of a drug and its metabolite, to the selection of LC and MS conditions (including mass resolution) will be discussed using the data obtained with a model lactone drug and its hydroxy acid metabolite.
Jemal
M
M
Bioanalytical Research, Metabolism and Pharmacokinetics, Bristol-Myers Squibb Pharmaceutical Research Institute, P.O. Box 191, New Brunswick, NJ 08903-0191, USA. jemalm@bms.com
Ouyang
Z
Z
D002851:Chromatography, High Pressure Liquid; D006880:Hydroxy Acids / Q000032:analysis*; D007783:Lactones / Q000032:analysis* / Q000378:metabolism; D013058:Mass Spectrometry; D019821:Simvastatin / Q000031:analogs & derivatives / Q000032:analysis
D006880:Hydroxy Acids; D007783:Lactones; C063287:simvastatin acid; D019821:Simvastatin