Vial Cap Septum Resealibility after Puncture by LC Sample Manager Needles

Importance of the Topic

Analytical workflows often require repeated sampling from the same vial over extended periods.
In such scenarios, the septum’s ability to reseal after needle puncture is critical to maintain sample integrity and accurate quantitation.
Failure to reseal can lead to evaporation of volatile analytes or solvents, altering concentration and impacting data quality.

Objectives and Study Overview

This study assessed how different vial cap septa affect analyte concentration stability following multiple punctures by LC sample manager needles.
Two injection systems were compared:

• A fixed-loop injector on a Waters ACQUITY UPLC.
• A flow-through needle (FTN) injector on a Waters ACQUITY UPLC H-Class.

A reversed-phase QC reference material containing both volatile (naphthalene) and non-volatile (amitriptyline) compounds in an aqueous volatile solvent was used.

Methodology and Instrumentation

An ACQUITY UPLC and an H-Class system were calibrated, and each received 48 certified Qsert vials loaded with QC reference solution.
Six cap/septum types were tested (pre-split and solid variants of TruView, LectraBond, and LCMS caps).
Each vial was sampled eight times at 8-hour intervals over 56 hours.
LC conditions included a 5-95% acetonitrile gradient with 0.1% formic acid, a CSH C18 1.7 µm (2.1×50 mm) column at 30 °C, 0.6 mL/min flow, UV detection at 254 nm, and 1 µL injections.

Main Results and Discussion

Fixed-loop injector:

• Volatile analyte (naphthalene) peak areas decreased by 48–68% across septa types due to evaporation.
• Non-volatile analyte (amitriptyline) peak areas increased by 4–22%, reflecting solvent loss.
• Pre-split septa (especially TruView and LectraBond) showed relatively better resealing for non-volatile analyte stability.

FTN injector:

• Naphthalene loss ranged from 26–36%, approximately half the loss seen with the fixed-loop injector.
• Amitriptyline changes remained within –0.5% to +2.3%, indicating minimal dilution effects.
• Solid septa and LCMS pre-split variants performed best, with resealability maintaining analyte levels within ±3%.

The smaller puncture diameter of the FTN needle (1.0 mm vs. 1.83 mm) enhances septum resealing.
Frequent septum replacement is recommended when tight control of volatile analyte concentration is required.

Benefits and Practical Applications

• Guidance for selecting cap/septum combinations to minimize sample loss over multiple injections.
• Supports quality control workflows that require periodic system suitability checks without transferring fresh samples.
• Helps laboratories optimize cap choice based on analyte volatility and injection frequency.

Conclusion

The ability of vial septa to reseal after puncture impacts the stability of both volatile and non-volatile analytes.
FTN injectors deliver improved resealing due to smaller penetration diameters.
Nevertheless, cap septa should be replaced as early as practical to ensure consistent sample integrity over time.

Future Trends and Applications

Anticipated developments include new septum materials or coatings engineered for repeated puncture resilience.
Automated septum monitoring or self-healing septa may emerge to further reduce evaporation effects.
Customization of septa selection software based on analyte properties could streamline method development for high-throughput laboratories.

Instrumentation Used

• Waters ACQUITY UPLC with fixed-loop injector
• Waters ACQUITY UPLC H-Class with flow-through needle (FTN) injector
• ACQUITY UPLC CSH C18, 1.7 µm, 2.1×50 mm column
• Empower 3 chromatography data system
• LCGC Certified Qsert vials

References

• Mallet C. Leachables from silicon septum: chromatography analysis. Waters White Paper, 2015.
• Mallet C. Leachables from vials: chromatography analysis. Waters White Paper, 2015.