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

✍ Scribed by Mohammed Jemal; Zheng Ouyang

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 161 KB
• Volume: 14
• Category: Article
• ISSN: 0951-4198
• DOI: 10.1002/1097-0231(20001015)14:19<1757::aid-rcm90>3.0.co;2-c

✦ Synopsis

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.