Analytical Sciences

Differential Estimation of Isomeric 2- and 4-methoxylated Estrogens in Serum by Matrix-assisted Laser Desorption Ionization–Tandem Mass Spectrometry

Ju-Yeon MOON,*,** Sun Ju KIM,*,*** Myeong Hee MOON,** Bong Chul CHUNG,* and Man Ho CHOI*,***

*Future Convergence Research Division, Korea Institute of Science and Technology, Seoul 136-791, Korea
**Department of Chemistry, Yonsei University, Seoul 120-749, Korea
***Department of Biomolecular Science, University of Science and Technology, Daejeon 305-333, Korea

As a simple and rapid method for small-molecule analysis, matrix-assisted laser desorption ionization coupled with linear ion-trap tandem mass spectrometry (MALDI-LTQ-MS/MS) was used to differentially quantify 2- and 4-methoxyestrogens in spiked serum samples. Both 2- and 4-methoxyestrogens were consistently identified using distinct analyte-matrix adduct [M+H+CHCA]⁺ precursor ions when a mixture of 10 mg mL⁻¹ α-cyano-4-hydroxycinnamic acid (CHCA) in 0.2% trifluoroacetic acid/70% acetonitrile was used as the MALDI matrix. Especially, unusual isomeric product ions from each precursor ion were characterized during MALDI-MS/MS analysis, which permitted differential estimations of isomeric 2- and 4-methoxylated estrone and 17β-estradiol. The calibration linearity was higher than 0.99 in the dynamic range, while the inter-day precision and accuracy ranged from 6.8 to 30.6%, and from 91.4 to 108.5%, respectively. The present technique could be used as a screening assay for 2- and 4-methoxyestrogens without the need for prior chromatographic separation, opening up possible applications in large-scale pharmacokinetic studies.

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