Beginner Nitrous Oxide with GC-ECD

[rholzem]

I am using a Shimadzu 2014 GC with a 63Ni ECD and a SS 2 m x 0.32 cm packed Porapak Q (80/100) column. The machine also has an FID, but I will not be using this because I am only interested in measuring Nitrous Oxide. The carrier gas is UHP nitrogen gas. I am currently trying to set up the device for measurement, but I am having trouble with setting the Total flowrate, column flowrate, and carrier gas flowrate, as the manual is not very helpful. The literature typically has between 30 and 40 mL/min, but I am not sure, which flowrate this is, or how to set this up. Does anyone have any recommendations or a good source for this type of information or could help me out? Also, as I mentioned, I will not be using the FID, so does anyone have any recommendations on what parameters to set for the FID while I am running the ECD?

Furthermore, recommendations on temperatures would be great. I am currently at a column temp of 80 C, detector at 295 C, and the injector and FID at 80 C. In most of the papers I have read, the detector is usually at a higher temp 330-350, but the ECD manual recommends not going higher than 300 C. Will this still be a high enough temp?

Lastly, I have injected 500 uL of standard into the machine, but my concentrations are all over the place. Some of the higher standards have lower peaks than the lower concentrations. Does anyone have an idea on what may be causing this? The standards have nitrous oxide, methane, and co2 (because that is all I have access to), but again, I am only measuring nitrous oxide.

I am sorry for the number of questions, but I am just starting this and am having difficulty finding any help.

Thanks.

[chromatographer1]

Drop your detector to 250°C !

You are not eluting C36 hydrocarbons!

You will damage the column heating the end of it in a detector that hot.

Nothing wrong in having the injector at 100°C. This eliminates any water condensation.

Sorry but I am not familiar with the Shimadzu 2014GC. I will let others assist you there.

best wishes,

Rod

[AICMM]

rholzem,

I too am not familiar with the 2014 so I am not sure how much I can help. Couple of comments though. Set your FID to 100 or 110 just to keep it warm enough to prevent any condensation. Get your self a flowmeter, manual or electronic to measure the flows you are interested in. With 40 mL of column flow rate, you probably do not need to add anything else in terms of flow to the detector.

Are you using a valve or a syringe to do your injections of gas samples? This could be a source of your problem with reproducibility.

Best regards,

AICMM

[rholzem]

Thank you all for your help so far. I am using a syringe, however, I can get some reproducibility when I inject the same sample multiple times, the samples just do not line up with the standard curve.

Ryan

[mflint]

Hello there,
I came across this forum while searching for some help on some GC peaks I cannot identify. It sounds like we have a similar system (here is an excerpt from my recent paper):
N2O concentrations were measured at the University of Florida with an Agilent Gas Chromatograph (7820-A) equipped with a µ-ECD (electron capture detector - 63Ni source, 350°C, makeup gas 5% CH4/Argon mixture) and an Agilent J&W GS-CARBONPLOT column (30 m length, 0.320 mm diameter widebore, 3.00 µm film) regulated at a temperature of 30°C and UHP N2 as the carrier gas. Calibration standards were prepared by diluting a 0.9700 ppm N2O standard in a He or N2 matrix to 0%, 25%, 50%, 75%, 100% N2O. Dilutions were made fresh before each analysis by injecting gases directly into pre-evacuated 75 mL glass vials. Gas concentrations in the headspace samples were converted to dissolved concentrations according to Weiss & Price [1980] and based on the temperature and salinity of the water. All N2O samples were collected in triplicate to assess the relative error of the head-space extraction collection method, which generated a relative standard deviation of < 0.2 µg N-N2O/L.

So, I have been measuring N2O concentrations throughout springs and groundwaters of the Upper Floridan Aquifer for the past 4 years – and this method has been great. However, after recently replacing my column, I noticed some peaks eluting right after my N2O peak that i can not seem to identify (keep in mind these are mixtures of natural gases extracted from natural waters. The recent peaks look like this (ignore the sharp peak right after the main peaks – this is our inlet switching off):

https://imgur.com/ieOcsZY

So, the peak I am interested in identifying is basically the shoulder peak off the main N2O peak. You can see this peak is variable in height, so this tells me whatever gas this is, is also variable in concentrations within the natural waters I am investigating. Any idea what this could be? Have you seen anything like this in your samples?