LC-MS/MS approaches for the assay of bis-quaternary pyridinium oximes used as AChE reactivators in biological matrices

Background: Extreme efforts are made for the structural diversification of oximes used as AChE reactivators. Co-administration of different oximes should also be considered as a solution in therapy. Consequently, development of selective assays of oximes in biological matrices is of major importance. Results: Three chromatographic separation mechanisms were evaluated: hydrophilic-interaction LC; mixed reversed-phase/cation exchange (DUET); and reversed-phase ion pairing based on per-fluorinated agents. MS was used to identify and quantify oximes. Alternative preparation of whole blood and plasma samples were used based on protein precipitation through addition of acetonitrile or ionic liquids. Quality characteristics of the proposed analytical approaches are discussed. Conclusion: The reversed-phase ion pairing based on per-fluorinated agents chromatographic separation mechanism and positive ESI-MS/MS detection produced the best results for the assay of bis-quaternary pyridinium oximes. LLOQ in the tenths of nanogram per milliliter range are achievable.