We have been producing blocked columns at an alarming rate. On investigation I noticed a pile of "chips' resembling graphite near the needle guide and on the needle spring assembly. Pursuing this further we noticed the "chip" on the plate seals and on the needle seal. We now belive these chips may be getting into the system. Has anyone else noted these 'chips"

Thanks
Ed

I have called this cokeing. It seems to occur when the injector is very hot and leaking air. It also seems to matter on volume and type of compounds being injected. 5ul or larger injections that are percent level PCB for instance seems to be able to produce significant carbon deposits. Also using ethylene glycol diacetate as your solvent can make it difficult to avoid. Frequent replacement of septa and good seals can help reduce the problem.