Synergistic integration of μ-SPE and ammoniated adduct-based MRM for sensitive UPLC-MS/MS quantification of PEG1000: a comparative study against in-source CID and application to zebrafish tissue distribution

A sensitive UPLC-MS/MS method was developed and validated for quantifying polyethylene glycol 1000 (PEG1000) in zebrafish tissues, featuring a systematic comparison of two MS acquisition strategies. Through comprehensive optimization, the ammonium adduct [M+NH 4 ] + of the representative 18-EO oligomer ( m/z 828.5) was selected as the precursor ion, achieving approximately fourfold higher signal intensity than [M+H] + . Critically, the conventional high declustering potential in-source CID approach monitoring fragment ions was outperformed by the optimized MRM method monitoring the intact ammoniated precursor, which demonstrated 2.7-fold signal enhancement and superior selectivity. The integration of micro-solid-phase extraction (μ-SPE) further improved method performance, yielding 1.5-fold signal gain and markedly reduced matrix effects compared to conventional protein precipitation. The fully validated method exhibited excellent linearity (0.5–50 μg/mL, r  > 0.995), accuracy, precision, and stability. Application to zebrafish tissue distribution studies revealed pronounced organ-specific accumulation following aqueous exposure to 200 μg/mL PEG1000, with highest concentrations in intestine tissue exhibiting a time-dependent increase, followed by muscle, while muscle maintained consistently low levels. This analytical platform, synergistically combining μ-SPE cleanup and ammoniated adduct-based MRM, offers superior sensitivity over in-source CID approaches and provides a practical framework for polymer bioanalysis, yielding critical insights into the in vivo fate of PEG-based compounds. The key novelties of this work are the following: (i) the first systematic comparison between ammoniated adduct MRM and high-DP in-source CID for PEG1000 quantification; (ii) the introduction of μ-SPE for sample preparation in zebrafish tissues, achieving 1.5-fold signal enhancement; and (iii) the successful application of this platform to reveal organ-specific accumulation patterns of PEG1000. Graphical abstract