Pre-slit septa provide a penetration aid for thick and dull needles and minimizes evaporation before injection, which can lead to concentration changes.
When using Waters™ and other autosamplers, it is crucial to note that non-slit septa can cause a vacuum in the vial if the needle is too snug with the septa hole and will withdraw more sample volume than the air that can replace it. This can result in inaccurate injection volumes. However, pre-slit septa allow sufficient air into the vial while the needle withdraws liquid, preventing a vacuum from occurring and ensuring proper injection performance by the instrument.
