Harmonizing Routine Oxylipin Profiling: A Multisite Evaluation of Inter-Laboratory Reproducibility

Significance of the topic

Oxylipins are low-abundance, structurally diverse lipid mediators derived from polyunsaturated fatty acids that modulate inflammation, vascular biology, and metabolic signaling. Because many oxylipins exist as regio- and stereoisomers at trace concentrations in biological matrices, sensitive, selective and reproducible targeted LC–MS/MS workflows are required for routine and large-cohort studies. Standardized, transferable methods reduce technical variance between laboratories and enable reliable cross-study comparisons and meta-analyses in clinical and translational research.

Objectives and study overview

This multisite study evaluated the reproducibility and robustness of a standardized oxylipin profiling workflow across three independent laboratories. Using an identical hardware and method configuration based on the Agilent Infinity III Bio LC coupled to the 6495D triple quadrupole MS, the authors assessed retention time stability, ionization performance and quantitative precision for a comprehensive targeted panel of oxylipins. The goal was to demonstrate method transferability for routine, high-throughput oxylipin analysis and to identify sources of inter-laboratory variation.

Methodology

• Sample preparation: Pooled human plasma was diluted in cold 20:80 methanol:water with added heavy-labeled internal standards, enriched by C18 solid-phase extraction (Agilent Bond Elut), dried and reconstituted in 50:50 methanol:water. Aliquots were distributed to three sites.
• Chromatography: Altura ZORBAX Eclipse Plus C18 column (1.8 µm, 2.1 × 150 mm) operated on the Agilent 1290 Infinity III Bio LC. Column temperature 40 °C, autosampler 4 °C, injection volume 10 µL, flow 0.350 mL/min. A binary solvent system with 0.1% acetic acid in water (A) and 90:10 acetonitrile/isopropanol (B) was used with a gradient optimized for oxylipin regioisomer separation.
• Mass spectrometry: Agilent 6495D triple quadrupole with 4th-generation dual-stage iFunnel. Dynamic multiple reaction monitoring (dMRM) targeted 191 analytes (17 heavy-labeled and 174 endogenous targets) with a minimum dwell time of ~10.1 ms. Source parameters were optimized using Cayman Chemical standards and MassHunter Compound and Source Optimizer.
• Quality approach: Heavy-labeled internal standards were distributed across the chromatogram to monitor retention behavior and ionization. Nineteen representative endogenous oxylipins spanning the elution window were used to evaluate retention time precision across sites.

Used instrumentation

• Agilent 1290 Infinity III Bio LC with Altura ZORBAX Eclipse Plus C18 column (1.8 µm, 2.1 × 150 mm).
• Agilent 6495D Triple Quadrupole LC/MS System with dual-stage iFunnel.
• Agilent Bond Elut C18 SPE cartridges for enrichment.
• MassHunter software (version 12.3) with Compound and Source Optimizer for MS tuning.

Main results and discussion

The standardized setup produced robust chromatographic separation sufficient to resolve many oxylipin regioisomers (epoxides, dihydroxy fatty acids, HETEs, HEPEs, DiHOMEs, EpOMEs, resolvins, etc.). Across the pooled plasma extract, 100 of the 191 target analytes were detected on at least one instrument; 80 analytes were consistently detected across all three sites. Nineteen representative endogenous markers chosen across the elution profile demonstrated highly consistent retention times between sites, with retention time relative standard deviations reported at under 0.1% RSD for the 80 analytes found across all labs.

Overlaying 20 consecutive injections of 12,13-DiHOME from each site illustrated exceptional short-term retention stability and reproducibility. Remaining differences in detection of low-responding analytes were attributed primarily to sample/analyte stability during shipment and minor variations in LC/MS performance for low-intensity targets.

Key takeaways and practical benefits

• Transferability: Using an identical LC/MS configuration and shared method parameters markedly reduced technical variability and supported inter-laboratory reproducibility for routine oxylipin profiling.
• Coverage and selectivity: The 191-target dMRM assay spans major biosynthetic pathways (AA, EPA, DHA, LA, resolvins) and employs transitions chosen for isomer selectivity, enabling detailed family- and isomer-specific analysis.
• Compatibility: The method integrates with standard C18 SPE extraction protocols and is compatible with other Agilent Omics workflows (polar metabolites, lipids, bile acids, acylcarnitines), facilitating multiplexed lab adoption.
• High throughput readiness: The use of dMRM with short dwell times and the iFunnel-enabled sensitivity supports high-throughput sample sets while preserving reproducibility.

Future trends and potential applications

• Expansion of labeled internal standards: Increasing the number and coverage of isotopically labeled standards will improve quantitation for low-abundance and closely eluting isomers.
• Standardized QC materials: Development of matrix-matched, multi-analyte QC materials for oxylipins would further harmonize inter-lab comparisons and support proficiency testing.
• Automation and sample logistics: Automated SPE and controlled cold-chain logistics will reduce variability related to sample handling and shipment.
• Advanced scheduling and software: Enhanced dMRM scheduling, retention time locking and library-based identification will streamline large-cohort analyses and reduce missingness for low-intensity targets.
• Cross-platform and database integration: Shared reference retention times, transition lists and open spectral libraries will facilitate meta-analyses and method adoption across laboratories and platforms.

Conclusions

This multisite evaluation demonstrated that a rigorously standardized LC–MS/MS configuration (Infinity III Bio LC + 6495D TQ) and harmonized sample preparation enable reproducible, high-throughput oxylipin profiling across independent laboratories. The workflow achieved stable retention times, strong isomer selectivity and consistent detection for a large subset of targets, making it suitable as a transferable method for research labs seeking to implement routine oxylipin measurements in clinical and large-cohort studies. Remaining variability for low-response analytes highlights the importance of sample integrity, adequate internal standards and continued optimization of sensitivity.

References

1. Strassburg K, et al. Analysis of oxylipins by LC–MS/MS. Analytical and Bioanalytical Chemistry. 2012.
2. Huynh K, et al. A comprehensive, curated, high-throughput LC–MS/MS analysis method. Agilent Application Note 5994-86263EN. 2025.
3. Rashan AM, et al. Title not provided. Nature Structural & Molecular Biology. 2025.
4. Yannell KE, et al. An End-to-End Targeted Metabolomics Workflow. Agilent Application Note 5994-5628EN. 2023.
5. Morlacchi P, et al. Deciphering the Microbiome: Targeted Method for the Detailed Analysis of the Plasma Lipidome. Agilent Application Note 5994-3447EN. 2021.
6. Silva B, et al. Quantification of Underivatized Acylcarnitines and Carnitine Intermediates using RP Chromatography and Ion Funnel Triple Quadrupole in Fecal Samples. ASMS 2025, Poster MP638.