Chromatography Forum

I am advised by Agilent application specialist that hydrogen as a carrier is recommended from 30 - 50 mls per minute column flow. At all but the slowest flow rate there is noticeable peak fronting (overload look). I want Gaussian peaks, but to try and achieve it I have to slow the column flow very low. Am I missing some basic fact like maybe that most hydrogen carrier gas methods have front edge leading peaks due to the higher recommended flow rates? I don't have any good chromatography data files which I can zoom in/out to see what the peaks normally look like on other peoples methods.

I think you are mixing up the unit sof gas flow. The optimun linear flow rate for hydrogen is 50 cm/s - depending on column diameter that is a volumn flow rate of about 1 - 3 ml/min. I doubt that it is physically possible to get a flow rate of 50 ml.min through an ordinary capillary column in a GC, but you could do it with a megabore column.

Yes indeed, in my haste I used ml/min instead of the cm/sec flow. My question remains about hydrogen flow velocity and peak fronting though.

As long as everything else is ok, hydrogen will not cause peak fronting. But is everything else OK?, that we cannot tell. We need to know what you are injecting, how, and how much, what column you have etc etc.

Are you running split? If so, have you increased the split ratio? How much material are you putting on column and what are your column dimensions.?

Best regards,

AICMM

Are you running split? If so, have you increased the split ratio? How much material are you putting on column and what are your column dimensions.?

Best regards,

AICMM

My column is a DB5 30 meter x 0.25 mm ID x 0.25 uFilm. I am injecting 0.075 ug onto the column after the 40:1 split is accounted for. An important aspect of this method is to be able to see impurities not simply an assay of a pesticide.

Are you running split? If so, have you increased the split ratio? How much material are you putting on column and what are your column dimensions.?

Best regards,

AICMM

My column is a DB5 30 meter x 0.25 mm ID x 0.25 uFilm. I am injecting 0.075 ug onto the column after the 40:1 split is accounted for. An important aspect of this method is to be able to see impurities not simply an assay of a pesticide.

Could be a problem with overloading the column.

https://www.restek.com/row/technical-li ... parations/

Quite a ways down that article it list typical column loading versus column diameter where a 0.25mm column is listed at 50ng on column, if you are at 75ng it may be slightly overloaded. Of course film thickness, stationary phase type and other thing do play into to also. That article is a very good reference for deciding what column to use for a particular analysis.