The influence of the syringe needle on the precision and accuracy of vaporizing GC injections

The discrimination of the high boiling components of a C9 to C44 alkane test mixture in a vaporizing injector (analysed with stream splitting on a capillary column) is mainly due to a selective elution of the sample out of the syringe needle. Different methods of handling the syringe needle are tested. The discrimination is quantitated and correlated with the material left in the needle. The poorest method of injection was found to retain the sample in the needle when the latter is introduced into the vaporizer. The sample should be pulled back into the barrel of the syringe and the needle allowed to warm up in the injector before the sample is transferred into it. The solvent flush technique may be preferred for components sensitive to the hot metal surface of the needle.