Sample multiplexing for increasing throughput for quantification of estrogens in serum by LC-MS/MS

Development of an accurate and sensitive assay for 2-methoxyestradiol using derivatization and liquid chromatography-tandem mass spectrometry

2-Methoxyestradiol (2ME) is involved in the pathogenesis of preeclampsia and antitumor activity. In addition to its low concentration in healthy human serum, presence of isomers makes quantification of 2ME for clinical research and laboratory medicine difficult. The objective of this study was to develop a highly sensitive and accurate method for quantifying 2ME using LC-MS/MS combined with derivatization with 1-(2,4-dinitro-5-fluorophenyl)-4,4-dimethylpiperazinium iodide (MPDNP-F). This approach significantly enhanced the detectability of 2ME in positive electrospray ionization-tandem mass spectrometry (ESI-MS/MS) and enabled the chromatographic separation of 2ME from isomeric metabolites possessing a methoxy group, including 4-methoxyestradiol, 3-O-methyl 2-hydroxyestradiol, and 3-O-methyl 4-hydroxyestradiol (3M4OH). Although the derivatized 2ME and 3M4OH were closely eluted under the optimized LC conditions, the different fragmentation patterns of these isomers during MS/MS allowed their distinction. The lower limit of quantification for 2ME was 2.5 pg/mL, indicating a satisfactory sensitivity. These findings demonstrated that this LC-MS/MS method combined with the MPDNP-F derivatization can provide accurate and highly sensitive quantification of 2ME.

Derivatization procedure of estradiol with a combination of MPDNP-F and 4-dimethylaminopyridine to generate product ion containing estradiol-skeleton for reliable determination of its serum/plasma concentrations by LC/ESI-MS/MS

The quantification of serum/plasma estradiol (E2) is useful for the diagnosis, pathological analysis, and monitoring of the therapeutic efficacy of estrogen-dependent diseases. In this study, an improved derivatization method using 1-(2,4-dinitro-5-fluorophenyl)-4,4-dimethylpiperazinium iodide (MPDNP-F) was developed and combined with liquid chromatography/electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS) for the sensitive and specific quantification of the serum/plasma E2. In the new method, the reaction time was reduced to 15 min from 90 min (two-step reaction in the previous method) by the direct reaction of MPDNP-F with E2 at 60°C in the presence of 4-dimethylaminopyridine (DMAP). DMAP served as the organic catalyst and had a less negative effect on the LC/ESI-MS/MS instrument compared to the non-volatile inorganic salt (NaHCO3), which was used in the previous method. The collision-induced dissociation of the molecular cation ([M]+) of the resulting derivative provided a product ion containing the E2-skeleton ([M-NO2-H]+), which significantly enhanced the assay sensitivity and specificity; compared to the dansyl chloride derivatization, which is the currently most-used derivatization procedure for the LC/ESI-MS/MS assays of E2, the MPDNP-F derivatization had significantly fewer interfering peaks and a clear and flat baseline in the serum sample analysis. The MPDNP-F derivatization-LC/ESI-MS/MS method enabled the precise and accurate quantification of E2 even at a 5.0 pg/mL concentration (lower limit of quantification) with a small sample volume (100 μL of serum/plasma) and had a tolerance for the matrix effect. This method was also proven to serve as a more sensitive and specific alternative to the clinically used chemiluminescence enzyme immunoassay.