OXYGEN SENSOR - AMI Oxygen Analyzer

Oct 8, 2023 Below is an oxygen graph from approximately midway through X395 to the end of X400. X400 was using an anaerobic glove bag, which consumes a lot of nitrogen every time an IW wholeround is processed. The nitrogen generator is able to produce very high quality nitrogen (~25 ppm oxygen with only the GCs using it) when there is very little flow. When flow is increased, it gets to the point that the nitrogen generator cannot keep up, and the quality drops a little bit, as can be seen in the X400 graph below. The glove bag use seems to raise the oxygen concentration to 150-300 ppm on average. This is still very good nitrogen - approximately 99.98 % nitrogen. 

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Sep 5, 2023 Typical X400 cyclicity in generator nitrogen quality caused by the anaerobic glove bag being inflated.

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Aug 24, 2023 AMI data monitoring software was installed back onto the CAHN computer. 

Jan 1, 2023 The sensor cell was replaced. The readings had been around 10-20 ppm for the duration of the expedition so far. A UHP nitrogen test was performed on the old cell, and the sensor only went to 5 ppm VERY slowly (over several hours). The new cell did not make a difference, readings still 10-20 ppm and very slow response to UHP nitrogen. Also the new cell only reached 7 ppm on the UHP nitrogen bottle.   

Dec 12, 2021 Replaced the sensor cell.

Oct 27, 2020 Replacement instructions for the Oxygen Analyzer sensor cell. We use type T-2 sensor. Click the images to enlarge them. More information can be found in the AMI Oxygen Analyzer Manual. The sensor contains hazardous chemicals (see AMI T-2 oxygen sensor SDS), thus old sensors should be disposed of as hazardous waste. 

Dec 10, 2019 (Copy of an NGA1 note - included here also since the oxygen sensor played a key part in the experiment.) 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. 

Quote from the Parker DB-10 Nitrogen Generator Manual "Nitrogen produced by PSA Nitrogen Generators contain Argon which is also inert. Therefore, when mentioning Nitrogen purities, the composition of the product gas is determined by the residual Oxygen content. Ex. 1% Oxygen in product gas is equivalent to 100%-1% = 99% (Nitrogen + Argon)."  Also, "Purities of 99.9 to 99.99% requires oxygen analyzer upgrade and must be sampled directly from the Nitrogen Storage Tank (NST 101) using copper tubing."

Dec 3, 2019 The oxygen analyzer was replumbed. The nitrogen now tees off to the coulometer before the oxygen analyzer, and the oxygen analyzer vents into the lab.

Nov 1, 2019 The sensor was replaced. 

AMI Oxygen Analyzer Manual

AMI T-2 oxygen sensor SDS