Chromatography Forum

Hey guys, Im having a problem seperating the peaks that elute before my temp program kicks in. I am testing for VOCs under EPA method 624 and the compounds giving me trouble are vinyl chloride, chloroethane, ethanol, bromomethane, and a few others.

I am using a 7890A
HP-5MS column .25um by 30mm
Constant flow rate of 1.2 ml/min
Front inlet temp 230C
1:20 Split
holding 35C for 4 minutes


I was previously running a 1:100 split and constant pressure of 19(mmtorr i think?) which had my flow rate up to 2.4, but was also giving me better seperation.

Any insight would be appreciated, thanks!

If you download the app note below and use the GC conditions and column listed, you should be good to go....

http://www.estanalytical.com/presentati ... 20Note.pdf

Funny, I just changed to the column (20x.18) described in that article last night. I will try these parameters today, thanks!

Jon

Jon

You are running at twice optimum flow at 1.2 mL per minute.

You need plates. Set your flows at near optimum for more plates, or go to a smaller id COLUMN.

best wishes,

Rod

The new column is working great. Best calcurve ive had in a long time, thanks for all of your guys help! The parameters given were spot on and the flow was definitely too high.


Jon