Cone voltage induced in‐source dissociation of glucuronides in electrospray and implications in biological analyses

Abstract

Glucuronidation is a common mechanism in drug metabolism. In-source dissociation of glucuronides in electrospray generates fragment ions identical to those of the precursor ions of the original drugs. The effect of experimental parameters on the process was investigated in the present study using both commercially available compounds and glucuronides generated from microsomal glucuronidation incubations. It was found that cone voltage was the most critical parameter contributing to in-source fragmentation of both O- and N-glucuronides, whereas both the desolvation temperature and the source temperature had little effect. Additionally, the extent of in-source dissociation varied for different glucuronides and could be minimized by lowering cone voltage. As demonstrated in real examples, minimizing in-source dissociation can lead to higher sensitivity in detecting glucuronides in biological samples. In addition, product ions resulting from in-source dissociation of glucuronides potentially interfere with accurate determinations of corresponding drug levels if chromatographic separation is not adequate. For cases in which chromatographic separation of glucuronides from the original drugs is not readily achieved or high-throughput analyses are desired, interference caused by in-source dissociation can usually be eliminated simply by using lower cone voltage. This approach has been proven to be effective in the analysis of more than 100 glucuronides generated from in vitro microsomal incubations.

UDP-Glucuronosyltransferase 1A1 Is the Principal Enzyme Responsible for Etoposide Glucuronidation in Human Liver and Intestinal Microsomes: Structural Characterization of Phenolic and Alcoholic Glucuronides of Etoposide and Estimation of Enzyme Kinetics

“…It is noted that the MS responses of EPG, EAG1, and EAG2 were apparently different from each other at the same concentrations (EAG2 Ͼ EPG Ͼ EAG1), and also quite different from their parent compound, etoposide. The cone voltage-dependent sensitivities for the quantification of intact etoposide glucuronides by LC-ESI-MS are consistent with the analysis of other glucuronides in biological samples (Yan et al, 2003). Collectively, the effects of cone voltages on the determination of sensitivity by LC-ESI-MS are chemical struc- …”

Farnesol is glucuronidated in human liver, kidney and intestine in vitro, and is a novel substrate for UGT2B7 and UGT1A1

“…The mass spectrum of the farnesyl glucuronide is shown in Figure 3(a). The fragmentation peaks are consistent with the breakdown of a glucuronide with characteristic peaks at m/z 113, 157 and 175, which is common for glucuronide fragments in negative-ion mode electrospray [26,27]. No farnesol aglycone ion peak was observed in the fragmentation (which is expected in negative-ion mode), but one of the peaks can be attributed to a farnesyl glucuronide fragment (m/z 279).…”

Determination of SCH 211803 by nanoelectrospray infusion mass spectrometry: evaluation of matrix effect and comparison with liquid chromatography–tandem mass spectrometry

“…Although interference could also be eliminated by judicious sample extraction in nanoelectrospray infusion analysis, LC tends to offer a much higher separation power than that obtainable with sample clean-up. An alternative strategy for reducing interference from labile metabolites which may convert to the parent drug molecule in the electrospray source (such as glucuronide, N-oxide and sulfate) is to use a lower than normal declustering potential in the first vacuum region of the mass spectrometer immediately after the ion source [14]. However, this approach usually results in lower analyte signal intensity or higher background due to insufficient desolvation of solvated ions and does not always completely eliminate the interfering fragmentation process.…”