GC NGA1 Agilent 7890A

Owned by jr_suhonen
Last updated: May 27, 2024
7 min read

May 24, 2024 NGA1 was used for the final phase of the helium conservation experiment.

First, the instrument was checked with a STD B run on helium as makeup. Baseline ~15 pA. See image below.

 

Next, generator nitrogen was connected to NGA1 FID makeup inlet. Similar cyclic baseline abnormalities appeared (see image below) as were observed back in 2020 when the first generator nitrogen tests were performed.

 

Agilent recommended trying to purify the generator nitrogen with a nitrogen purifier trap. A trap was installed, and it did indeed make a significant difference in the baseline. It immediately cleaned out the “bumps”. It did take two days for the baseline to stabilize around 115 pA.

 

STD B was run as a test (see image below). The STD B chromatogram came out as it does with helium as makeup gas. The only minor difference seen in STD B (He vs. N2) was an approximately 1.5 min long bump in the baseline around 3 minutes into a run (lab air was also run several times, and the same bump in the same place was observed). This bump is not present when helium is used as makeup. No explanation was found for the bump, and it remained for the duration of the experiment. It did not affect the integration of the peaks though. 

 

At the end of the experiment the instrument was returned to its original settings with helium as makeup gas. STD B was run to confirm normal operation.

 

Conclusion: Generator nitrogen can be cleaned up enough with a nitrogen purifier trap to be used as makeup gas.

 

Apr 16, 2023 To exclude TCD from the pdf report, go to the Signal page in method, and uncheck the #2 Back signal (TCD) box.

 

 

Feb 7, 2021 New helium and nitrogen traps were received for all GCs. The traps are awaiting installation. 

 

Nov 25, 2020 Generator nitrogen was connected to the FID makeup inlet. See below for baseline after 24 hrs. There is still a little troubleshooting we have to do here. One option would be to purchase a Universal nitrogen trap, RMSN-2 that would remove oxygen, moisture and hydrocarbons. We have an RMSN-2 on the back of GC2, as well as an RMSH-2, which purifies helium. GC2 does use generator nitrogen as μECD makeup, but further testing will be needed to determine if the same setup would work with an FID. 

 

May 3, 2024 Added note: When switching FID makeup gas from helium to nitrogen, you also have to change it in the method. 

 

 

Nov 24, 2020 UHP nitrogen was run from a bottle by fumehood #1 into the makeup inlet. This produced a perfectly flat baseline around 15 pA, just like helium.

 

Nov 23, 2020 Reconfigured helium and nitrogen lines and installed a 3-way valve to enable us to run nitrogen through the columns instead of helium while the instrument is idle. This would save us a lot of helium when we have a layup or a long transit and the GCs are not being used. We will investigate the potential effects of the standby nitrogen generator N2 flow on the columns before implementing the procedure. For now we are leaving the valve on helium. Also added a ball valve to enable shutting off nitrogen to NGA1.

 

Oct 22, 2020  Changed the report chromatograms to display full frame instead of ranges. This displays all features of the FID and TCDs chromatograms to the pdf reports instead of zooming in on only a small portion. To replicate this, within ChemStation's Data Analysis tab, click the results of a sample, make sure the "Calibration" button is selected to display report options. Click the "Specify Report Calculation and Report Style" > "Signals" > then click the "Full" radio button within the "Ranges" group.

Jul 22, 2020 The current method to use is 378T_NGA1.m

Dec 10, 2019 Expedition 385 staff had detected 2% (20 000 ppm) oxygen in the nitrogen from the nitrogen generator on NGA1. The oxygen sensor never detected more than 10 ppm oxygen in the nitrogen. The nitrogen generator was rebuilt in San Diego port call. More information on the nitrogen generator service call and the nitrogen generator can be found in Support Equipment & Shop Tools > Nitrogen Generator.

NGA1 was calibrated and used for tests attempting to solve the aforementioned "oxygen" issue. The following tests were performed:

  1. The nitrogen generator nitrogen line was run directly into the NGA1 injection port. Several repetitions of the measurement consistently resulted in a 20 000 ppm oxygen peak. The experiment was repeated by running a nitrogen line from directly before the oxygen sensor (the oxygen sensor constantly detecting less than 3 ppm oxygen). Same result. A 20 000 ppm oxygen peak. Oxygen and argon retention times are very close to each other, and we currently have no means of separating them. To rule out any possibility of argon introduction into the nitrogen line, we even shut down and bled the argon line from TBULK. After argon having been off for 24 hours the nitrogen generator nitrogen was run on NGA1 again repeatedly, with every result consistently showing a 20 000 ppm oxygen peak. The nitrogen generator can concentrate argon a little bit but can it really concentrate it all the way to 20 000 ppm?  

  2. A nitrogen line was run directly into the NGA1 injection port from the UHP oxygen free nitrogen in the lab. No oxygen was detected. This measurement was also repeated several times on several days, alternating with the nitrogen generator nitrogen measurements. The results were consistent. No oxygen in the bottle nitrogen, 20 000 ppm in the generator nitrogen. We do believe we are seeing an argon peak, but we really have no way of proving it. 

  3. The oxygen sensor was tested with the UHP nitrogen. The reading was similar to the nitrogen generator nitrogen reading, 1-5 ppm.

  4. To prove that argon generates an “oxygen” peak, an argon line was run directly into the NGA1 injection port. The result was a 1 000 000 ppm peak (100% argon) exactly at the oxygen retention time. The molesieve column in NGA1 has no capability of distinguishing between oxygen and argon. This was proven later on in another experiment in which UHP oxygen free nitrogen was collected in a sealed headspace vial and spiked with a 5 ml oxygen free argon injection. The argon showed up in the chromatogram as an oxygen peak.

  5. The NGA1 molesieve column was changed out as per the Lab Officer's recommendation, to rule out potential issues with the column. After conditioning the column and performing a calibration, the same experiments were repeated with the same results. The old column was placed in the new one's box and clearly labeled "used but good". It is stored in the column cabinet and will be fine to use as a spare as there did not seem to be anything wrong with it.

  6. Once NGA2 was installed, most of the experiments above were repeated on it with very similar results. We think the nitrogen generator is fine, and what we are seeing is an argon peak, but we haven't proven it. 

Dec 4, 2019 Changed out the molesieve column as per the Lab Officer's recommendation. The old column was placed in the new one's box and clearly labeled "used but good". It is stored in the column cabinet and will be fine to use as a spare as there did not seem to be anything wrong with it. The behavior of the GC continued the same with the new molesieve column in place. 

Aug 31, 2019

  • The method to use now is based off of NGA_UPDATEDVALVE_STANDARDMETHOD.m. Using a prior method will result in FID baseline disturbances due to erroneous valve and pressure control module (PCM) configurations in the software.

  • We see some carryover after running high standards (I ran STD C last night and did a "No Injection" today and still found peaks for C1-C6 in the FID signal). So we need to troubleshoot that still.