Chromatography Forum

Okay so I am trying to use a shimatzu 2014 gc to run acetylene reduction assays and I am having multiple problems. At this point I have not even gotten to actually start the assays I am still working on a standard curve for ethylene and having no luck at all. The procedure I am working off of for a std curve can be viewed here (http://cmgm.stanford.edu/biology/long/f ... ASSAYS.pdf) My first and biggest problem is a sensitivity issue, at the second dilution point the ethylene peak is undetectable. I also have large methane peaks in samples that should not have any methane and another "peak" that not only shouldn't be present but is not really a peak. Thus far I have tried adjusting the sensitivity and changing the sample size with no real change in peak sizes.

Pictures to follow this coming monday

If you're trying to separate these things at 80 °C, perhaps lowering the oven temperature will help you a great deal.

Ethylene and acetylene will be difficult if you are not using the correct column for your separation. I have an app. note that shows you can separate these 2 from each other on a Poraplot Q phase (25 m x 0.32 mm x 10 µm), hydrogen carrier gas. Ethane is not in the mixture displayed so I don't know where it comes out and how it might complicate things. It's an isothermal run at 25 °C.

The 5-type-phase separations (Rtx-5, DB-5, SPB-5, etc.) I see in my app. note book (the old Chrompack volumes) are not good for ethylene and acetylene.

Got this from the Restek website.

Column Rt®-Silica BOND, 30 m, 0.32 mm ID (cat.# 19785)
Sample Custom DCG gas standard
Diluent: Nitrogen
Conc.: 1 mole percent
Injection
Inj. Vol.: 15 µL split (split ratio 35:1)
Liner: 2 mm straight Sky® inlet liner (cat.# 23313.1)
Inj. Temp.: 250 °C
Oven
Oven Temp.: 60 °C (hold 2 min) to 175 °C at 2 °C/min
Carrier Gas He, constant flow
Flow Rate: 3.3 mL/min
Detector FID @ 260 °C
Make-up Gas Flow Rate: 50 mL/min
Make-up Gas Type: N2
Hydrogen flow: 40 mL/min
Air flow: 400 mL/min
Data Rate: 10 Hz
Instrument Agilent 7890A GC

1. = Methane
2. = Ethane
3. = Ethylene
4. = Acetylene

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