There is no option to give Carrier gas interms of lenear velocity in all my Agilent GC instruments.

Hello,

It is understandable that there is difficulty when the analysis information provided is in cm/sec and the input requires ml/min.  When provided certain basic parameters the GC has the capability to calculate linear velocity. We chose this method.

You can do the conversion outside of the software if the SOP doesn't provide it. 

The suggested workaround is to download and install a small application that will do the conversion for you.  A free GC Calculator App for iPhone is available from Agilent at

http://www.chem.agilent.com/en-US/promotions/Pages/GCapp.aspx

The Headspace Control Option is available and currently supports the HS7694 (G1289B and G1290B) and also the G1888.  A newer revision of the Headspace Control Option is being worked on that will support the HS7697 headspace sampler.

I hope this information is helpful.

Dot

Hi Satya,

To convert from a linear velocity to a volumetric velocity is not overly challenging but it is a bit involved. Agilent does put out a pc version of the calculator that dot referenced (if the issue was that it was an app). They claim it's not windows 7 compatible but I run it on Win 7 with no issues. Here's the URL:

http://www.chem.agilent.com/en-US/Technical-Support/Instruments-Systems/Gas-Chromatography/utilities/Pages/GCPressureFlowCalculatorPCRev205.aspx

If you want the hand calculation here's how it works.

F = A*Uo

Where:

A is column area

Uo is outlet linear velocity

A = p*d^2 / 4

Where:

d is column diameter in cm (not mm)

Note: Dividing by 4 takes into account that we're using diameter instead of radius

Uo = U / j

U is average linear velocity (30 cm/s for you)

j is a pressure correction factor

j = 1.5*((p_i / p_o )^2 - 1) / (p_i / p_o )^3 - 1)

Where:

p_i is ABSOLUTE inlet pressure (typically we measure this in terms of the gauge, so you'll add atmospheric pressure to the inlet pressure to obtain the absolute pressure)

p_o is the absolute outlet pressure (just atmospheric unless you're running an outlet into a vacuum)

Note: pressures in kPa

Put it all together:

F = p*d^2*U / 4*j

F will have units of mL/s, so multiply by 60 to get mL/min. (or just use 1800 cm/min instead of 30 cm/s)

Finally, to correct for the temperature of your oven.

F*T_a/T_c

Where:

T_a is ambient temp (298K, typically)

T_c is oven temp (also in K)

If you wanted to do it all in one go your equation would look like this:

Note this is using U in cm/min, you'll have to multiply by 60 if you use the cm/s value

I put all this in an excel sheet if you want to work out an example.

Hope this helps,

Nate