Chromatography Forum

Peter Apps,

Thank you for your insight and knowledge on this topic. I must apologize if you thought my comment about sending barbs my way was directed to your posts. It was not. Your responses have been helpful and directed at my question. My post was directed to the unhelpful post from the consumer guy.

The manufacturers method I am trying to run doesn't restrict my use of consumables. Liners can be chosen at my discretion and thats why I was trying to get input on optimizing my results.

I am using a megabore column and thats why I think I am getting favorable results with a 2mm straight liner with no glass wool. I am going to try some of the suggestions you made to better understand the effects of liner selection while running a particular analysis.

Thanks again for the insight.

With solvents that have high heats of vaporization and produce a lot of vapour, changing the pre-injection dwell time (when the needle is in the inlet before the plunger drops) can help a lot. The Agilent default fast cold needle injection is often not optimum for tricky solvents. I would be surprised if the manufacturers method even mentions autosampler settings (except injection vol) so you should have room to play.

Peter

Hi Peter,

Could you elaborate more on the use of pre-injection dwell time in injecting solvent that produces lot of vapor 'cos it's pretty new technique to me that I am not aware of before? Do you mean that I could still inject a certain volume of sample/solvent (say methanol, water, etc) which its vapor volume exceeds the liner volume without any problem? Thanks.

Hubert

Hi Hubert

What increasing the dwell time does is to give the needle time to heat up by conduction from the hot inlet. The hot needle then heats the injected liquid, which gives better vaporization. If the needle gets above the boiling point of the solvent you get boiling in the needle, and a spray of hot droplets, which may or may not be a good thing. Flash vaporization is actually a stupid way of handling a sample, it's very sensitive to small changes in conditions, and hard to replicate in different set ups, and impossibel to model. PTV is way better.

As I have said in other threads I am somewhat sceptical of the impact of vapour volume overflow. With split injections at any kind of sensible split ratio it is a complete non-issue. What IS a problem is the response of EPC gas controls to the pressure pulse that you get when the sample is injected.

Peter

If you're concerned about the expansion of water I would suggest a pulsed split on a 4mm s/s liner.

I hope that the new Agilent multimode inlet comes to replace the standard split/splitless configuration. The PTV abilities are really nice not just in terms of providing a more versatile way of handling sample vaporization but also because it can heat and cool more rapidly between injections in a sequence.

If the sample is in water PTV might well be worth a try, it would certainly save the EPC units from having to cope with pressure pulses - condensation in the vent line and filters is likely to be a major issue though.

Peter