Chromatography Forum

Hello everyone! I am using an Agilent G1888a connected to an Agilent 6890N with an FID detector to run some solvent analysis according to <USP> 467.

The headspace analyzer is hooked up via a transfer line directly into a S/SL inlet and is controlled via MPC as I do not have an auxiliary EPC on the 6890N.

I am having a difficult time getting the analyzer to produce any peaks. I know it, most likely, has to do with the analyzer flow rates. I can direct inject directly into the inlet and obtain beautiful chromatography, so I know it is not on the GC side.

My thought is it has to do with either the flow of gas coming from the analyzer and or the vial pressurization settings.

Unfortunately, I have not found any good sources for dialing these values in.

Can anyone help me with pointers? I do have available electronic flow meters and leak detectors for troubleshooting.

What is wrong with Inlet pneumatics, why manual?

In short - you would NOT get any peaks from HSS when:
* Split vent is opened
* Inlet head pressure is same or greater than one in HSS input

I do have inlet pneumatics on the gc which controls flow through the column. I just don’t have electronic control of the flow through the HSS which, as I understand it, is fairly common in this type of setup. I know how to set the flow through the transfer line by watching the split flow but don’t know what the optimum flow is for the transfer line when the column flow is set to 2ml/min at a 10:1 split ratio.

I do have inlet pneumatics on the gc which controls flow through the column. I just don’t have electronic control of the flow through the HSS which, as I understand it, is fairly common in this type of setup. I know how to set the flow through the transfer line by watching the split flow but don’t know what the optimum flow is for the transfer line when the column flow is set to 2ml/min at a 10:1 split ratio.

Most applications will use the inlet EPC to control flow through the HSS and Inlet. You cut the incoming flow line going into the inlet, use that as the gas flow into the HSS, then the transfer line from the HSS goes into the line on the Inlet that was cut. This way it sets the flow through the entire system.

If you are using constant flow on the column without this setup, then the inlet pressure is going to increase as the oven temperature increases, and once it is higher than the pressure set by the MPC on the HSS, you could be getting flow going back into the HSS instead of forward through the column.

Ok. Cut through the inlet line. Assumed it was 1/16”. Turns out slightly bigger. Is Agilent the only place I can get the fittings to fit this line?

Ok. Cut through the inlet line. Assumed it was 1/16”. Turns out slightly bigger. Is Agilent the only place I can get the fittings to fit this line?

Uh oh. There are two lines: one is inlet and one is septum purge outlet. The septum purge is slightly larger than 1/16th, the inlet supply IS 1/16th. If you cut the septum purge you will likely need to replace the weldment.

If you remove the green septum nut look for which of the two lines goes 'further in'--that is the inlet supply.

Ugh, yes the inlet line is the smaller 1/16" one.

I know the nut and ferrule of a 1/16" Swagelok won't fit over the line, but if the thicker line will insert into the body of a 1/16" Swagelok union, then you could possibly use a drill to enlarge the hole in the nut and in a Vespel/Graphite ferrule and reconnect them.

If not Restek has replacement weldments
https://www.restek.com/catalog/view/3006

The other option is to use some solder and seal the line and not use septum purge, since you won't be puncturing it often you shouldn't need to worry about septum bleed.

Ok. Spliced into the other and plugged the septum purge line. Getting good pressure readings through HSS but not building pressure on the inlet. Leak detector is not detecting any leaks. Next suggestion? This seems to be going from one problem to another. New weldment on the way but don’t understand why it isn’t working. Verified flow through the transfer line.

Did you check the flow at the split vent? or at the column outlet? If you show flow there but no pressure on the inlet then it could be a bad sensor in the EPC.

G1888 can be run with manual pneumatics. There would be a needle on the end of the transfer line and then inserted through the septum when you wanted to use. Methods were usually 10-15mL/min on the transfer line. We would pull out the transfer line and put a flow meter right on it. Once adjusted to 10 or 15 mL/min, reinsert into the inlet.