Date: 14-JULY-2017   Last Updated: 27-JANUARY-2026

Unexpected retention time shifts are often linked to inconsistencies in the mobile phase composition reaching the pump. One common—and easily overlooked—cause is the presence of residual solvents in the mobile‑phase lines from previous users or methods.

Verify Mobile‑Phase Line Integrity

Before starting any analysis, confirm that each solvent line is actually immersed in the correct mobile phase required for your method. If a previous method used different solvents, remnants may still remain in the tubing.

Purge Lines Thoroughly

If there is any possibility of solvent mismatch:

• Purge each solvent line to waste using the mobile phase designated for the method, continuing until the line has been completely displaced by the correct solvent (typically several system volumes).
• Prevent any *non‑method solvents from entering the column, as their introduction can alter stationary‑phase selectivity or cause retention‑time variability.
• Thoroughly flush the injector needle and sample loop to remove residual solvent and eliminate the risk of analyte carryover.

*Special Considerations for Single‑Component Mobile Phases

Methods requiring 100% organic or 100% aqueous conditions are especially sensitive to contamination:

• Even small amounts of carryover from another mobile‑phase line (e.g., water entering an organic‑only method or vice versa) can significantly alter retention behavior.
• This contamination may lead to inconsistent, irreproducible, or unexpected chromatographic results.

Performing a full purge of all active lines with the specified mobile phase eliminates this variable and ensures consistent baseline conditions.

Summary

Retention time stability depends on mobile‑phase consistency. Ensuring that all solvent lines are properly purged with the correct mobile phase is a simple but critical step in preventing unexpected retention time shifts and maintaining method reproducibility.