Determination of pibutidine metabolites in human plasma by LC-MS/MS

Overcoming ionization effects through chromatography: A case study for the ESI-LC–MS/MS quantitation of a hydrophobic therapeutic agent in human serum using a stable-label internal standard

“…This modification alters the hydrophobic properties and therefore the retention time. This phenomenon was reported as an isotope effect in other examples in the literature [37][38][39].…”

“…The most popular published methods to remediate these effects are optimizing sample preparation (such as liquid-liquid extraction (LLE) and solid-phase extraction (SPE)) or chromatographic techniques [9,18,[32][33][34][35]. Recently, stable isotopically labeled internal standards have become increasingly popular as a tool for compensating potential and known matrix effects due to their nearly identical chemical and physical properties to the target analyte [12,[36][37][38]. However, in certain cases a deuterium labeled IS has demonstrated differing ionization potential compared to the analyte which has compromised the accuracy of analyte concentration due to the slight shift in retention time between analyte and SIL IS and the retention relationship with the co-eluting endogenous material [38].…”

Does a stable isotopically labeled internal standard always correct analyte response?

“…It was noticed that carvedilol-S and -R eluted slightly later than their respective internal standards (retention time of 1.93 min for carvedilol-S versus 1.91 min for its SIL, and retention time of 2.16 min for carvedilol-R versus 2.14 min for its SIL). As stated before [14,15], it is believed that the deuterium isotope effect caused the slight separation between the analyte and its deuterated analogue in the reversed phase chromatography. The deuterium atoms were found to be less lipophilic and the deuterated IS thus eluted slightly earlier on a reversed phase chromatography system.…”

“…This is thought to be due, in part, to the replacement of the carbon bound hydrogen with deuterium, which slightly alters the lipophilicity of the molecule, and hence the retention time of the deuterium labeled compound during reversed phase separations. This phenomenon is commonly known as an isotope effect [13][14][15].…”

Stable isotopically labeled internal standards in quantitative bioanalysis using liquid chromatography/mass spectrometry: necessity or not?

“…3 On the other hand, several assays have been reported describing the use of an analogous internal standard with excellent results and there are reports describing the disadvantages of SIL internal standards. 1,4,5 In this article…”