Column flow calc help

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

3 posts Page 1 of 1
I'm currently using a DB5-MS column that is 30m x.25x.25 with hydrogen carrier gas at 1.2psi on a 5890 with a 5972 MS. I have to run the head pressure at 1.2psi to keep the flow at around 1ml/min, which seems a bit low to get reliable results from the EPC flow controller. I'd like to add a short .1um guard column to the transfer line, but I can't find any calculations for flow when using a hybrid column like this. I tried 1 meter to start, but I had to raise the pressure way to high to get the right holdup time, which surprised me. Any suggestions?
Controlling pressure with a MS and hydrogen can be tricky on a 30m column. I've had a lot of experience using guard columns, and I would be nervous connecting a 0.25mm column to a 0.10mm guard. Have you considered a 20m 0.18mm, 0.18um column? With a 1.0mL outlet flow, that would put your head pressure over 8psi at 40C starting oven temp.
Regards,

Christian
As above, we use a 20mx0.18mmx0.36um film Rxi-5SilMS column with hydrogen in our MS and it works very well. At 50c oven temperature the head pressure is around 10psi for 1.2ml/min. If you want to use a guard column you can add a couple meters of a 0.25ID column and the flow will still be the same as without since the 0.18 is the more restrictive portion of the flow path. I have even used a 0.53 guard column when injecting Ethyl Acetate with good success.
The past is there to guide us into the future, not to dwell in.
3 posts Page 1 of 1

Who is online

In total there are 11 users online :: 0 registered, 0 hidden and 11 guests (based on users active over the past 5 minutes)
Most users ever online was 599 on Tue Sep 18, 2018 9:27 am

Users browsing this forum: No registered users and 11 guests

Latest Blog Posts from Separation Science

Separation Science offers free learning from the experts covering methods, applications, webinars, eSeminars, videos, tutorials for users of liquid chromatography, gas chromatography, mass spectrometry, sample preparation and related analytical techniques.

Subscribe to our eNewsletter with daily, weekly or monthly updates: Food, Environmental, (Bio)Pharmaceutical, Bioclinical, Liquid Chromatography, Gas Chromatography and Mass Spectrometry.

Liquid Chromatography

Gas Chromatography

Mass Spectrometry