The occurrence of peak tailing and poor reproducibility can occur with standard syringe injection of liquid samples into the GC injection port. It occurs with microvolume syringes when the minute sample being delivered from the syringe forms droplets which wet the syringe needle rather than forming a jet of nebulised liquid from the needle tip. As the needle is rapidly withdrawn from the injection port, it is wiped by the septa causing slow secondary vaporisation near the cool septum cap. Not only poor peak shape is observed but sample size reproducibility will be poor. Position of quartz wool in the injection liner Resolution of the problem is achieved by effectively wiping the sample from the needle tip during the injection.
High speed autosamplers commonly use quartz wool as the liner packing.
The position of the quartz wool should be adjusted to achieve effective wiping of the needle. In this position, the quartz wool offers no wiping of the needle tip. The adjustment of the packing position does not alter the boiling point discrimination characteristics of the injection system. Adjusting the position of the injection point packing so that the needle tip is wiped during injection, improves peak shape, reproducibility and linearity without adversely affecting boiling point discrimination.