Chromatography Forum

Hi,

I have a 5890 without the EPC, and Im wanting to set a split ratio of 50:1
The carrier gas that I'm using is Helium. I am using an electronic flowmeter to measure flow rates.

The column I am using is a RXi-35sil 15 meter 0.25 ID

Column headpressure is at 20 psi
The measurement from the septum purge vent is 2ml/min
The measurement from inlet vent is 17 ml/min
The carrier flow rate at the detector with the air and hydrogen off is 10.1 ml/min

Attached are pictures of all the guages as well as the chromatogram of a standard solution at 116.2 ppm

I've seen various numbers recommended for both column head pressure as well as carrier flow, I'd like to learn how those two variables are generally determined, and how to set calculate my current split ratio based off the data above, and what I need to do to make it a 50:1 split ratio.

Thanks in advance for any help or suggestions on improving my GC skills.

When measuring the flow rate of the carrier did you have the aux gas off?

You need the Agilent flow calculator:

https://www.agilent.com/en-us/support/g ... alculators

Install it on your computer. It's a lifesaver for manual systems like this. For you, 20 psig is way too high unless your oven temperature is very warm to start. To get a more reasonable linear velocity for a 15 m x 250 µm column:

Head pressure = 6.5 psig (at 40 °C oven temperature)

This gets you to about 28 cm/s linear velocity. Good for helium.

To get 50:1 split at this head pressure, measure 49.25 cc/min out the split vent. The Agilent calculator will help you determine what you need. Good luck.

Restek has a calculator too and you don't need to install it:

http://www.restek.com/ezgc-mtfc

Adding to what r6banjo said.

To change the split flow you turn the total flow knob - it's an idiosyncracy of back-flow regulated inlets.

Peter

Like they said, and you will get the hang of it. Not too bad, and these are great GCs.

Someone here still got some vintage 5890 and HPIB parts available, super reasonable too. http://chromforum.org/viewtopic.php?f=7&t=27106