Help setting up a 5890 with split vent

[firkinslab]

Hello,

I am trying to set up an HP 5890 to run long chain FA analysis. My column is already installed but I have no idea where to begin when it comes to setting up my split vent, purge vent or other flows. Does anyone recommend a particular place to start or a list of steps to take?

I only have experience with a packed column and I am rather perplexed at this point.

Thanks!

firkinslab

[Don_Hilton]

Septum purge flow is to sweep past the septume and keep garbage from the septum out of your chromatography. This is typically set when the instrument is installed and does not requrie adjustment. The manual should have a number. Somewhere in the back of my memory 1 - 3 mL/min seems to be around the right rate.

Split flow depends on sample concentration. This can range anwhere from about 10 times the volume through the column to 200 times the volume through the column. It depends on column dimensions and sample concentration.

If the vendor of the column has an applicaitons note describing an applicaiton similar to yours - including analyte concentration, see what conditions were used in the application note. Or if you are following a published procedure, get what you can from that.

If you are not able to find parameters, then set the column flow to give a linear velocity of between 23 and 35 cm/second. If your samples have analytes in the parts per thousand range, start with a higher split ration (200:1). More diluted samples take a lower split ratio. If you need a split ratio below 10:1, go to a splitless injection. For that the purge off time should be long enough to allow about one volume of gas to pass from the inlet to the column, then the split ratio is set to quickly purge the inlet of any remaining vapors.

[firkinslab]

Don_Hilton,

Thank you for the quick response! Our machine has knobs for setting the septum purge, the total flow (split vent), and column head pressure. Before someone disconnected the GC and messed with the settings by adjusting the knobs, the machine seemed to work well. The split ration was 100:1 so I would need to use the split vent. I am just not certain where to start. Do I start by setting the split vent and then the purge vent and then check other flows? I have tried a few things but the linear velocity as tested by methane isn't coming out at the right time.

Thanks!

[skunked_once]

Please list details about your column and carrier gas. Assuming it is a 0.25 x 30 mm column, I would first set the split flow at 100 mL/min, then set the column pressure at 20 psi, then check the septum purge and set to 1-3 mL/min. Heat your oven to the initial column temperature and use a methane peak to check linear velocity. Adjust the column pressure up or down to get about 35 cm/sec.

[firkinslab]

Thanks. The column is .25 mm, .2uM film thickness, 100 m long
Carrier gas is He.

firkinslab

[firkinslab]

When checking linear velocity, should we light the FID or only run methane?

[Consumer Products Guy]

When checking linear velocity, should we light the FID or only run methane?

Light the FID flame so the methane will be detected.

I'd start by making the split flow about 50 ml/min (check with flow meter or bubble meter) using the Total Flow knob. Make the pressure about 10 psi with the Column head pressure knob. You determine the column flow, use Agilent's free Flow Calculator software (or rig up something and actually measure). So with the column flow and the split flow, adjust as necessary, calculate the split ration from the total flow (split + column) and the column flow.

You likely will not need to mess with purge flow knob, but 1-3 ml/min is right.

[firkinslab]

Thanks for the reply.
We set flow of air and hydrogen and then injected methane for carrier gas (helium) linear velocity. Air, hydrogen and helium were on and FID was lit. The manual program we used was 175 C for 15 min. Methane came out at different times: around 10 -11 min. We turn up the column head pressure and methane came out at 9 min, which is close the target of 8.4 min.

Then we took out column and trimmed it because it's been long since the column was trimmed and conditioned last time. After we did trimming and reinstalled the column, the methane did not come out.

I am not sure how the chromatography should look like. Please see the pic below. Could anyone tell me how good the baseline should be after conditioning if there are not other serious problems with the instrument?


However, when we looked at the real time window, it (partially) looks like this:


We know that in the real time window, the y axis stands for pa, which indicates the signal and is not the same as the y axis in the final graph (top pic). But shall we say, the baseline is good by looking at the real time window and ignore the final graph?

When checking linear velocity, should we light the FID or only run methane?

Light the FID flame so the methane will be detected.

I'd start by making the split flow about 50 ml/min (check with flow meter or bubble meter) using the Total Flow knob. Make the pressure about 10 psi with the Column head pressure knob. You determine the column flow, use Agilent's free Flow Calculator software (or rig up something and actually measure). So with the column flow and the split flow, adjust as necessary, calculate the split ration from the total flow (split + column) and the column flow.

You likely will not need to mess with purge flow knob, but 1-3 ml/min is right.

[AICMM]

You are not lit. Hydrogen and air flame should give you moisture out the castle of the FID so check it with a vial (or, ugh, I didn't say this, your glasses in your hand.) If not lit, use your ignitor even if not connected since it will choke off flows to help you light.

Set a high split vent flow using total flow. Your head pressure should read something if your system is plumbed correctly. Then set column flow (with H2, make-up and air off) somewhere close to where you want to be using the column head pressure knob to establish a back pressure on the column. Then turn everything else on and establish linear velocity. Then, when you calculate the column flow, turn up or down the total flow to establish your split ratio. Have to have enough split flow to be able to play with column back pressure.

You sound like you have a flow meter, you do right?

Best regards,

AICMM

[firkinslab]

Dear AICMM,

Thank you for your reply.

We decided to pull out the spring and push it in for another time because we noticed the FID was lit, but the button "SIG 1" on the right side of the machine showed value 0.0 after we made sure we lit the FID (we have a mirror to check the steam coming out of the flame). Also, the baseline did not response at the time we lit the FID (usually there would be a high peak at the time of igniting).

After pushing the spring harder to better connect with the FID collector, we tried to light the FID again. There is a number over 1.0 showed on the screen of the machine when we pressed the "SIG 1" button. Also, a peak showed up when we ignited the FID. So we think the signal was picked up by the spring and transferred to the peak on the real time window.

We checked and adjusted the air and hydrogen flow on the detector. They are 300 mL/ min and 30 mL/ min.

Then we decided to inject methane to check the carrier gas flow. But no peak came out within 15 min after trying a second time.

Any ideas why is there no peak for the methane?

You are not lit. Hydrogen and air flame should give you moisture out the castle of the FID so check it with a vial (or, ugh, I didn't say this, your glasses in your hand.) If not lit, use your ignitor even if not connected since it will choke off flows to help you light.

Set a high split vent flow using total flow. Your head pressure should read something if your system is plumbed correctly. Then set column flow (with H2, make-up and air off) somewhere close to where you want to be using the column head pressure knob to establish a back pressure on the column. Then turn everything else on and establish linear velocity. Then, when you calculate the column flow, turn up or down the total flow to establish your split ratio. Have to have enough split flow to be able to play with column back pressure.

You sound like you have a flow meter, you do right?

Best regards,

AICMM

[AICMM]

firkinslab,

Unless you have really clean air, 1.0 is still not lit. If using compressed air, it has at around 4ppm methane so that will give you 5 - 20 pA signal right off the bat. Make sure you are lit with a vial.

Clarification on my previous post is in order, sorry. When I say use the ignitor, I meant push the button in even if you are using a lighter. That way you are cutting down your flows while trying to light the FID.

However, the spike you are getting suggests your glow plug is working because your FID sounds like it is picking up the electron emission from the glow plug filament (very common.) So, in theory, you should light just by using the button. Okay, so try blowing across the castle (recommended to me first here on the forum) (in a shear direction, not over the castle) and see if you don't ignite and stay lit. If not, I would ask two things. Are you getting column flow (and how much) and are you using make-up gas. You need about 20-40 mL out the "column" (remember 1950's detector) which can be 5 of carrier and 15 of make-up or it can be 20 carrier and no make-up. Let's see where that gets you. Hopefully lit.

Best regards,

AICMM

[firkinslab]

AICMM,
I did not make it clear enough. I apologize. When I said the signal was over 1.0, I meant it jumped to large random numbers sometimes such as 500, 15, 5, etc., and small numbers such as 1.5, 2.5, etc. But the number always stayed above 1.0. We did see a signal of about 5 pA when we ignited the FID. So we believe the FID was lit.

We injected hexane for 6 times and the hexane came out at between 10.5~12.9 min.

Then, we injected methane for several times, which came out at 13.1- 13.5 min. But sometimes methane did not come out at all. What could be the cause for this unstable appearance of methane?

PS: We have hydrogen air and helium on. Helium is the carrier gas. We don't have makeup gas.

firkinslab

[daniel_aut]

Clean the liner and replace the wool inside(cleaning=silanisation).If not possible use a new liner.

[Peter Apps]

AICMM,
I did not make it clear enough. I apologize. When I said the signal was over 1.0, I meant it jumped to large random numbers sometimes such as 500, 15, 5, etc., and small numbers such as 1.5, 2.5, etc. But the number always stayed above 1.0. We did see a signal of about 5 pA when we ignited the FID. So we believe the FID was lit.

We injected hexane for 6 times and the hexane came out at between 10.5~12.9 min.

Then, we injected methane for several times, which came out at 13.1- 13.5 min. But sometimes methane did not come out at all. What could be the cause for this unstable appearance of methane?

PS: We have hydrogen air and helium on. Helium is the carrier gas. We don't have makeup gas.

firkinslab

Methane will always elute more quickly than hexane, so whatever peaks you are seeing are probably not due to what you think they are.

You need to be certain that you have gas flow through the column - remove it from the detector and dip the end into some clean solvent. If you have gas flow you will see bubbles. Reconnect to the detector. Then you must be sure that the FID flame is burning. Try to light it - you should hear a little pop as it ignites. Hold a cold shiny surface above the chimney; condensation shows that the flame is lit. With carrier gas flow and a flame you will see a peak for methane. Set the split ratio at about 10:1 and inject 100 ul to make sure that there is enough to produce a peak. If the flame will not light temporarily decrease the air flow and then increae it again when the flame lights.

Peter

[MSCHemist]

Wow 100ml/min. I keep my 5890 at about 13ml/min and always inject 10:1 split. If you abosultely have to have that high of a split I'd consider switching to nitrogen as a carrier or installing a switching valve before the inlet so you can blow nitrogen when you are not running samples and just switch to He when running samples.