Chromatography Forum

I'm seeing some lower responses than usual for the late eluting PNAs on my latest calibration. DDT breakdown is low, PCB and Benzidine checks pass; so I don't think it's a dirty system. Other analytes don't seem effected as much (the ones that are always bad are predictably bad, the ones that are always good seem pretty good).

I'm actually wondering if the injection port temperature is reading high somehow, and it isn't getting up to its normal temperature. Anyone ever have that issue with 6890?

I increased the injection port temperature from 250 to 265, and the PNAs looked better. I thought it was going to be bad for the more reactive analytes, but they didn't look like they were effected much.

That leads me to wonder what inj port temps others use for 8270, with DCM as the solvent. Most of the methods I've seen stick with 250.

I'm also curious if anyone has tried ramping it. I'm not sure if that would accomplish anything, since I've never heard of anyone doing it. It seems like it would have to be sensitive to timing: especially with a spitless injection. You'd have to give the injection port enough time to reach its final temperature before you opened the split vent and ramped the oven, right?

Ramping only works if you have one of the LVI inlets, they have low thermal mass and can change temperature quick enough, a regular inlet heats too slowly.

Have you cleaned out the exit hole for the split vent at the inlet? If those get crud in them you can see such losses. Another thing I found is a dirty source can actually lower and broaden those late eluting PNA analytes just like having inlet problems.

I run inlets anywhere from 250c to 280c, depending on how the injections look, each instrument is unique so have to tune it in to what works best.

Do you have glass wool in the liner, or glass cyclo? Those can help the late eluting analytes. I switched to the glass double taper cyclo liners a few year ago. I have about 50 of them and have been using the same ones for about three years now. I just bake them at 500c in a muffle furnace for a few hours to clean them and they are like new. I am injecting 8270 at 1:5 split and see very little breakdown, and what breakdown I do get is usually because the column needs trimming. If Benzoic acid goes away might need to remove a whole loop of column to get it back. Nitro phenols are also indicators of contaminated columns. If a few loops of column removed won't bring them back then time for a new column.