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LC/LC‑MS Carryover Hunter

Systematically eliminate carryover, not just "wash harder."

Identify carryover sources (needle/seat, rotor seals, dead volumes, inadequately chosen wash solvents) and verify fixes with blanks and component swaps.

CommunitySubmitted by CommunityWork20 min

INGREDIENTS

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PROMPT

You are OpenClaw. Ask for the analyte class, autosampler model, current wash solvents, and a blank-after-high chromatogram series. Provide an isolation plan (column vs injector vs solvents), then propose wash solvent selection, hardware checks (needle/seat/seals), and a validation protocol with acceptance thresholds.

Pain point

Peaks appear in blanks following high samples, producing false positives and biasing quantification.

Repro/diagnostic steps

  1. Run: high sample → blank series; quantify carryover decay.
  2. Isolate: injector/autosampler vs column vs solvent contamination using bypass/swaps.
  3. Inspect hardware: needle guide/seat, seals, and tubing connections for "reservoir" volumes.

Root causes (common)

  • Inadequate wash solvent strength or wash duration.
  • Worn injector/rotor seals and contaminated needle/seat components.
  • Poorly seated fittings creating dead volumes that retain sample.

Fix workflow

  1. Choose wash solvents based on analyte chemistry; verify needle wash is actually applied.
  2. Replace/clean wear parts on a maintenance cadence (rather than only reacting).
  3. Reduce dead volumes by reseating fittings and simplifying plumbing.
  4. Validate with a standardized carryover test sequence.

Expected result

  • Carryover in post-blank falls below method acceptance thresholds and remains stable over time.

References

  • https://help.waters.com/help/en/product-support/alliance-is-system-support/715008450/CBAFCF3.html
  • https://www.chromforum.org/viewtopic.php?t=79744&view=next
  • https://knowledge1.thermofisher.com/Mass_Spectrometry/Mass_Spectrometry_Knowledge/Carryover_and_Contamination
Tags:#lcms#chromatography#contamination#instrumentation