Spectrus: Exact mass search returns no hits when mass tolerance is set too narrow

Description
Users perform an exact mass search in Spectrus (e.g., using IXCR or Search Structure by mass against a local database or formula finder) and get “no hits” even for compounds that are known to be present. The underlying issue is that the mass tolerance is set too tight relative to the instrument’s mass accuracy or calibration state.

Solution

1. Review instrument mass accuracy
   • Check the typical and current mass accuracy of the xC/UV/MS system (e.g., ±2–5 ppm for well‑calibrated HRMS, or higher for less precise setups).
   • Confirm whether calibration has recently drifted or not been performed.
2. Inspect search settings in Spectrus
   • Open the exact mass or formula search dialog.
   • Note the current mass tolerance setting (ppm or Da).
3. Adjust to realistic tolerance
   • Increase tolerance from an overly strict value (for example, 1 ppm) to a value consistent with instrument performance (e.g., 5–10 ppm, or 0.01–0.1 Da for low‑resolution instruments).
   • Rerun the search.
4. Verify known compounds
   • Use a test peak whose identity is already known.
   • Confirm that with the adjusted tolerance, the correct hit appears at or near the top of the result list.
5. Save updated search defaults
   • If possible, save the adjusted tolerance as default for that instrument configuration or user profile.
   • Document recommended tolerances for each instrument type in your internal guidelines.
6. Combine mass with other criteria
   • Encourage users to also consider isotopic pattern, retention time, and fragmentation pattern for final identification, not mass alone.