title: Mechanistic studies on the use of 2H- and 13C-analogues as internal standards in selected ion monitoring GC-MS quantitative determination--butalbital example.
abstract: As a part of our study on the use of isotopic analogues as the internal standard (IS) for the quantitation of drug analytes, this article reports on the performance characteristics of 2H5-butalbital and 13C4-butalbital with particular focus on (1) determining and comparing the effectiveness of the 2H- and 13C-analogues in serving as the ISs for quantitation; (2) understanding the "cross-contribution" phenomenon underlying the effectiveness of selected ion pairs used for quantitation purpose; and (3) examining whether the same characteristics, observed in our preliminary report for the secobarbital/2H5-secobarbital/13C4-secobarbital system, also exist in the butalbital/2H5-butalbital/13C4-butalbital system. Adapting similar procedures applied to our previous study on the secobarbital system, we observed that (1) both labeled analogues (13C4-butalbital and 2H5-butalbital) cause more significant cross-contributions to ions designated for butalbital than butalbital to the labeled analogues; (2) compared to 2H5-butalbital, 13C4-butalbital appears to cause less cross-contributions to ions designated for butalbital; (3) cross-contribution between the following ion pairs are minimal: m/z 200/196, 199/195, 185/181 (13C4-butalbital as the IS) and m/z 201/196 (2H5-butalbital as the IS). It is also concluded that the butalbital/2H5-butalbital system exhibits the same concentration dependency phenomenon observed in the secobarbital/ 2H5-secobarbital system, that is, ratios of ion pairs designated for these two isotopic analogues (resulting from routine gas chromatography-mass spectrometry protocol) increase as their concentrations are diluted. (In parallel with the secobarbital/13C4-secobarbital system, the butalbital/13C4-butalbital system does not exhibit this phenomenon.)
authors.affiliation: Department of Forensic Sciences, Central Police University, Taoyuan, Taiwan.
authors.forename: W T
authors.initials: WT
authors.lastname: Chang
authors.forename: R H
authors.initials: RH
authors.lastname: Liu
mesh_terms: D001463:Barbiturates / Q000032:analysis* / Q000737:chemistry; D002138:Calibration; D002247:Carbon Isotopes; D003903:Deuterium; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D011786:Quality Control; D012016:Reference Values
chemical_list: D001463:Barbiturates; D002247:Carbon Isotopes; D003903:Deuterium; C004470:butalbital