Methanol-Associated Matrix Effects in Electrospray Ionization Tandem Mass Spectrometry

Abstract

Background: Matrix effects can profoundly reduce the performance of electrospray ionization mass spectrometry. Preliminary observations indicated that the methanol used in the mobile phase could be a source of differential ionization or ion suppression. Methods: Drug stability studies, analysis of biological extracts, mixing experiments, and postcolumn infusions were used to test 9 commercial methanols for ionization differences in liquid chromatography-tandem mass spectrometry assays for immunosuppressants. Area responses for the drugs and internal standards were compared for mobile phases prepared with each selected methanol. Postcolumn infusion experiments were performed to confirm the degree of ionization differences occurring at the ion source, and to evaluate the proportions of ammonium, sodium, and potassium adducts. Results: The decrease in signal for the immunosuppressant drugs was shown to result from differential ionization associated with the selected methanols. Product ion intensity varied by 10-fold among the methanols tested. For sirolimus, tacrolimus, and mycophenolic acid, the percentage change in ionization was the same for the drug and its corresponding internal standard. Postcolumn sirolimus infusion evaluation revealed that a 1000-fold analyte concentration difference did not affect ionization. The proportions of ammonium, sodium, and potassium adducts of sirolimus precursor ions differed in relation to the source of methanol. Conclusions: Organic solvents used in mobile phases and extract preparation of biological samples may be associated with ion suppression, affecting adduct formation and assay sensitivity.

Liquid chromatography-tandem mass spectrometry applications in endocrinology

“…Therefore, high-purity reagents and solvents are preferred for all mass spectrometric methods (Annesley, 2007).…”

Simultaneous Screening and Quantification of 29 Drugs of Abuse in Oral Fluid by Solid-Phase Extraction and Ultraperformance LC-MS/MS

“…A low volume of extract (10 L) was injected into the UPLC-MS/MS system, which provided a good resolution of the compounds and resulted in only low MEs for most of the drugs (online Supplemental Table 1 and Table 3). The selected brand of methanol has been shown to exhibit a low degree of ion suppression (14 ). The instrument also benefited from the low amount of loaded matrix, and periods of approximately 1 month between cleaning the cone were achieved.…”

Principles and Applications of LC-MS/MS for the Quantitative Bioanalysis of Analytes in Various Biological Samples

“…In many cases, however, the isotope-labeled compounds are not always available and the alternative structural analogues should be considered and evaluated carefully before use including the consideration of inter-subject differences (Taylor, 2007). Nine commercial methanol used in HPLC eluting solvents were evaluated for signal suppression of sirolimus, tacrolimus, and MPA in MS/MS detection (Annesley, 2007). Product ion intensity was found to vary by 10 folds among the methanol tested.…”