Pre and post inject delay

[dlbenach]

Does anyone have experience using pre or post inject delay when injecting a sample? I've tried it a couple of times and the results were either poor reproducibility between injections or very poor peak shapes. This seems like a good tool to have, but I'm not sure when it should be tried.

[James_Ball]

Does anyone have experience using pre or post inject delay when injecting a sample? I've tried it a couple of times and the results were either poor reproducibility between injections or very poor peak shapes. This seems like a good tool to have, but I'm not sure when it should be tried.

If you have a very high boiling analyte or solvent and you are using solvent focusing where the column temperature is held below your solvent boiling point then the delay may help to evaporate all of your solvent and analyte better. If you are not using solvent focusing then a post delay will be allowing more analyte to evaporate from the needle even after the major portion has evaporated from the injected solvent which is already moving down your column, this will cause tailing problems. Pre injection delay will cause fronting if your solvent is very volatile as the solvent still in the needle will evaporate prior to the bulk being injected.