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- Posts: 224
- Joined: Fri Jun 22, 2012 2:51 pm
I'm using a 6890 with FID to run alcohols and a couple other analytes that don't work well by P&T (1,4-dioxane and cyclohexanone). These are aqueous injections.
I'm using a ZB-Wax Plus 30 x 530 x 1.0 column.
Oven starts at 50, holds 1, 10C/min to 80, 20C/min to 170.
Inlet is at 170C, detector at 250C.
Nitrogen is used as the carrier gas.
I've tried different things with the injector. In the past, on our 5890, we had always done 1ul splitless injections. But I need really high column head pressure to avoid (in theory) solvent expansion backflash. That causes lousy peak resolution and means I'm putting a lot of nitrogen into the detector (even if the makeup gas is off).
Generally I've been trying to do splitless at 15 psi, but with smaller injections.
I've tried reducing the injection volume to 0.2, but when I do that, I seem to get inconsistent results. Out of ten repeat injections, most will line up real well, but one or two will vary from the others by 10-20%.
i tried changing out the standard 10ul syringe for a 5ul one, which allows me to do either 0.5 or 0.1 injections (these are the options the autosampler gives for that syringe size). At 15 psi, I still get occasionally inconsistent response from the injections, though it does seem better.
It's not clear to me how well split mode helps deal with solvent backflash. I have tried doing 1:1 splits using 1ul and 0.5 ul injections, but see similar results.
Anything I can do to get more consistent results from repeat injections?
Bonus questions:
We're using a 0.53 column just because that's what was always done here. Not sure why. I'm thinking of trying something smaller next time I order so I don't need so much head pressure. Thoughts?
Why is dioxane so erratic? Even when other compounds behave well, it seems to be all over the place.
I'm using a ZB-Wax Plus 30 x 530 x 1.0 column.
Oven starts at 50, holds 1, 10C/min to 80, 20C/min to 170.
Inlet is at 170C, detector at 250C.
Nitrogen is used as the carrier gas.
I've tried different things with the injector. In the past, on our 5890, we had always done 1ul splitless injections. But I need really high column head pressure to avoid (in theory) solvent expansion backflash. That causes lousy peak resolution and means I'm putting a lot of nitrogen into the detector (even if the makeup gas is off).
Generally I've been trying to do splitless at 15 psi, but with smaller injections.
I've tried reducing the injection volume to 0.2, but when I do that, I seem to get inconsistent results. Out of ten repeat injections, most will line up real well, but one or two will vary from the others by 10-20%.
i tried changing out the standard 10ul syringe for a 5ul one, which allows me to do either 0.5 or 0.1 injections (these are the options the autosampler gives for that syringe size). At 15 psi, I still get occasionally inconsistent response from the injections, though it does seem better.
It's not clear to me how well split mode helps deal with solvent backflash. I have tried doing 1:1 splits using 1ul and 0.5 ul injections, but see similar results.
Anything I can do to get more consistent results from repeat injections?
Bonus questions:
We're using a 0.53 column just because that's what was always done here. Not sure why. I'm thinking of trying something smaller next time I order so I don't need so much head pressure. Thoughts?
Why is dioxane so erratic? Even when other compounds behave well, it seems to be all over the place.
