Chromatography Forum

I have been running a 5890/ECD with a 30m x .32mm column with Nitrogen carrier for PCB analysis. The peaks were not as sharp as I would like, so I have switched to a 30m x .25mm column. I made no gas adjustments. I injected methylene chloride vapor to check flow but I get no signal change at all. I injected a pcb std and got no peaks at all. I recut the column ends. Still no luck. The flows measured at the detector exhaust are as follows: Carrier 10ml/min, makeup 35ml/min. Is it possible that the .25 column is too small?

... The flows measured at the detector exhaust are as follows: Carrier 10ml/min, ....

Are you kidding ? Your column is capillary !

Your carrier linear velocity is more then 200 cm/s for 320 µm column.
And optimum for nitrogen is 12-20 cm /s.

Nitrogen isn't the best carrier gas to use. What is your make up gas and what is the flow? Helium or hydrogen works much better and will give you much sharper peaks. I use hydrogen gas with a flow of around 3mL/min for PCB analysis and all of the peaks come off very sharp. My make up gas is nitrogen at 30mL/min.

jss37992,

what are your column dimensions?

My make-up is Ar/Methane at 35ml/min

I'm well aware of the preferred gases, and the Van Deemter curves.

I would drop the carrier flow to 1-3 cc/min. The 10 cc/min on a .25 column likely requires an extremely high inlet pressure - on a 5890 inlet, it might just be losing everything out the septum purge.

On most all of my methods I use 30 meter 0.32mmID columns connected to a 5 meter guard column. My carrier flows vary, but generally are within 1-3 mL/min depending on which method I am running.

For a 5890 ECD you will need make up gas. That detector was designed for packed columns. As I recall the flow range through the detector is 30-60 cc/min.

sllimbri65,

Let's not worry about the "esoterics" of column flow and carrier type just yet, shall we? Let's see if we can even get a detector response. First, pull the end of the column out of the detector, cool and off, and see if you get nice bubbly stream out the end. If so, then re-connect everything paying special attention to distances (very important in ECD detector) and snug fit and bring up to moderate temp (say 250.) Then shoot 5 uL of room air. Should get a nice fat peak. If not, then either the detector is not on, connected or working. Would be worth knowing split or splitless as well....

Then we go from there for flows and whatnot.

Best regards,

AICMM

sllimbri65,

Let's not worry about the "esoterics" of column flow and carrier type just yet, shall we? Let's see if we can even get a detector response. First, pull the end of the column out of the detector, cool and off, and see if you get nice bubbly stream out the end. If so, then re-connect everything paying special attention to distances (very important in ECD detector) and snug fit and bring up to moderate temp (say 250.) Then shoot 5 uL of room air. Should get a nice fat peak. If not, then either the detector is not on, connected or working. Would be worth knowing split or splitless as well....

Then we go from there for flows and whatnot.

Best regards,

AICMM

That was very nice. Many of us come here for just that kind of no nonsense approach. Thank you.

I pulled the detector end of the column and measured it this time. Now I have peaks. I have switched back to hydrogen carrier and am proceeding that way. Thank you.

So do we conclude that the 0.25 mm column was installed the wrong distance into the detector ? We are all trying to learn stuff, and feedback on solutions is very useful.

Peter

that was the problem