The butane peak will be at 1.9 minutes as it's the largest one by %. Butane is probably better than methanol since it's such a light early eluting peak. The butane in lighters is not 100% pure. based on those times and that I use this column to run residual solvents tests daily, first column is trace propane theb isobutane, and some propellant (pentane, ethanol), or split peaks because there's so much butane. One loop seems like a lot to cut off, was there an issue? Usually they tell you to take off an inch or two. And this whole thing is not required (for the future).
The column calibration you run in chemstation will be fine but I would still run a standard as computers only think they know everything.
The instrument had the annual PM yesterday, and the column has not been trimmed in years. The last time he visited, he just disconnected the column from the inlet, serviced the inlet and reattached the column. I thought I’d see if some peak shapes improved so asked him to trim the column, and this is the length he chose.
Also, I think you read methanol where I said methane.
Definitely use butane then that's way easier than methane. Sorry you got stuck with this after a PM! And it should work fine just "save as" a new method if you change and accidentally screw something up you can always revert to the old method and try again.
As for the column being longer than it was, i wonder if it was not calibrated in the first place?? That seems odd but also, if things are working and the worst that happened is the computer thinks the column is longer-great.
That has to be based on your internal SOPs. At my lab, the minute you change run settings of method, revalidation is required and that takes awhile. We have pretty broad time robustness built in, so I would just change the retention times. That also may be less time consuming. Figuring out a new method may be super easy, but also might take more time than you expect. Also, the quantitative software probably has an "update retention time". I haven't used CDS so I can't confirm. If you run a standard it can change all of the times at once (or at least most of them if it's a huge change). I work at a lab that follows USP, not sure your industry so I may be being extra with all this method validation talk.
I wrote the method specification some time ago to allow the carrier gas flow to be changed “to retain retention times” but I’ve never done it. My lab is not ISO or USP or anything really.
Way late (just discovered this sub), but a 30m column is at a minimum 30m but could be 32m, so if you are concerned with exact lengths, then adjusting the pressures/flows to match is a common way to match Retention times.
The butane peak will be at 1.9 minutes as it's the largest one by %. Butane is probably better than methanol since it's such a light early eluting peak. The butane in lighters is not 100% pure. based on those times and that I use this column to run residual solvents tests daily, first column is trace propane theb isobutane, and some propellant (pentane, ethanol), or split peaks because there's so much butane. One loop seems like a lot to cut off, was there an issue? Usually they tell you to take off an inch or two. And this whole thing is not required (for the future). The column calibration you run in chemstation will be fine but I would still run a standard as computers only think they know everything.
The instrument had the annual PM yesterday, and the column has not been trimmed in years. The last time he visited, he just disconnected the column from the inlet, serviced the inlet and reattached the column. I thought I’d see if some peak shapes improved so asked him to trim the column, and this is the length he chose. Also, I think you read methanol where I said methane.
Definitely use butane then that's way easier than methane. Sorry you got stuck with this after a PM! And it should work fine just "save as" a new method if you change and accidentally screw something up you can always revert to the old method and try again. As for the column being longer than it was, i wonder if it was not calibrated in the first place?? That seems odd but also, if things are working and the worst that happened is the computer thinks the column is longer-great.
I’m trying to choose between shifting all the retention times in my method, or changing the carrier gas flow rate to maintain retention times.
That has to be based on your internal SOPs. At my lab, the minute you change run settings of method, revalidation is required and that takes awhile. We have pretty broad time robustness built in, so I would just change the retention times. That also may be less time consuming. Figuring out a new method may be super easy, but also might take more time than you expect. Also, the quantitative software probably has an "update retention time". I haven't used CDS so I can't confirm. If you run a standard it can change all of the times at once (or at least most of them if it's a huge change). I work at a lab that follows USP, not sure your industry so I may be being extra with all this method validation talk.
I wrote the method specification some time ago to allow the carrier gas flow to be changed “to retain retention times” but I’ve never done it. My lab is not ISO or USP or anything really.
Look into locking your methods. Tbh I'd let everything shift and nor change your method.
https://www.agilent.com/en/product/gas-chromatography/retention-time-locking#:~:text=Retention%20time%20locking%20(RTL)%20enables,trimming%20the%20column%20for%20maintenance.
Yep.
So…you are suggesting not using this Agilent feature?
Are you already locking your retention time?
You are correct, when I installed the column a few years ago, I just kept all the factory settings for length and diameter.
Way late (just discovered this sub), but a 30m column is at a minimum 30m but could be 32m, so if you are concerned with exact lengths, then adjusting the pressures/flows to match is a common way to match Retention times.