ethylene std problems

[sinkdo]

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

[rb6banjo]

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.

[rb6banjo]

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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