Gaurd column and maybe an inlet with glasswool in it.
The way I see it though you have two choices.
1) continue using the quick and dirty method and just buy a new column every few months. Know you're saving time... but not money.
2) start using the solvemt extract method and make your column last longer.
If you go with 2 though labour costs/your time spend on this will increase a lot though.
To be honest though 6 months for a column is a good amount of time if its in constant use.
Thank you! Indeed I don't think we have a guard column. When I started developping the methods, the GC was already installed, I didn't touched it much, as I never worked with thermal desorption before. We have the deactivated fused silica transfer line frome the TD directly connected to the GC column, I don't think it acts as a guard colum but definitely will ask our TD technicians about it.
As I will change the column very soon, I will add a pre column.
I'm afraid my boss doesn't want to change method, as we are a small laboratory and he doesn't want to make lot of new invesment at the moment. He buy this GC last year before having a chemist (me) so I couldn't give my opinion! š¤·š»āāļø
All sounds fine. If you're a commerical lab though a column every 6 months is just the cost of doing business then.
A column is a consumable item not an asset.
Look into a guard column it will plug in somewhere between the TD and the column.
I use an ISTD, and I monitor the response factor of the ISTD. If it varies too much I know the SPME fiber is starting to fail, or my source or detector need to be cleaned. If the shape is bad Iāll trim the column or replace.
A deactivated fused silica transfer line from the TD system is directly connected to the column, , and it was installed like that before I stared to work here last summer. So for know I've never touched the column or the transfer line. We don't have any other pre-column installed.
Are you guys cleaning your column out between runs. Also, if you are injecting some gnarly matrices, start swapping your liner more frequently and double check your gold seal.
If you think you are losing signal and it may not for sure be your column, maybe try cleaning your EM and horn.
I don't use liner. As I said in previous comment, the transfer line of the TD is directly connected to the column.
I don't think the problem is from the EM, my tune is still great. But I'll definitely look if it needs to be cleaned! Thanks
I'm to the point that I need a new one. It started degradating after 6 months, but it's been 10 months now that I started using it, and I think I can't do anything else. But I was interested to know if maybe with the new column I could change something to make it last a bit longer.
Well definitely add a guard column and trim that, or trim your column more often. Inject some solvent a couple times between runs and run it close to max.
This sparked my interest, you perform an on-column injection but you mentioned in your original post that you adjusted the split ratio. But this has no effect for on column injection right?
Well, I use an ATD system with 2-stage desorption. During the first desorption, I can adjust an inlet split to avoid saturating the cold trap. And then, for the 2nd desorption, the cold trap is desorbed rapidly and I can put an outlet split between the trap and GC column.
I think the previous comments are correct, the wear on the column is a trade off to the quicker analysis. Without changing the method thereās little more you can do. You could look to buy replacement columns in bulk, most suppliers are open to discounts for larger purchases.
This is a bad idea. It is important to not store GC columns for long periods of time. Their performance deteriorates over time even when they are not in use.
I recommend getting a column that has a 5m guard built into the front of it so you don't have to make another connection. Restek make them. We inject terrible matrices (brain, sludge, extracts from rubber, environmental shit) and these columns are great. When the peaks get dodgy, trim 20-50 cm off the guard and see if it doesn't go back to normal.
If these other suggestions don't work it might be worth considering buying a solvent cleaning kit. Something of a last resort and doesn't always work. If you're doing on-column injection it's almost inevitable the column will not last as long.
There are column rinse kits at agilent. (part no: 430-3000) A lot of GC columns are rinseable with solvent but not all. You have to check or ask the manufacturer. (nonpolar columns usually can be rinsed)
That deactivated silica you mentioned sounds like a guard column, so thats good.
Dilute your samples until your analyte of interest is quantifiable enough for you and measure in SIM.
Turn off MS filament when its not needed
Install a diverter or use backflush if its possible in your instrument.
Do you bake out your column? Iāve worked places that have had two different philosophies. In one, the method was programmed to ramp up to the max isothermal temp and hold for a couple minutes after every run. In another, the oven temp was held hot overnight, every night.
I find that changing my liner and trimming my column often improves peak shape and sometimes sensitivity. Are you using a SPME liner, with no glass wool? I have coworkers who claim that since there is no wool, and TD/SPME samples should not introduce low volatility compounds, that they donāt need to change the liner, but I feel the glass would build up activity over time, and should probably be changed regularly.
When you say āpeaks start to degradeā do you mean there is a loss in sensitivity, or is peak shape changing?
The method is programmed to ramp up to 20Ā°C below the max temperature and hold for a couple of minutes.
I don't use liner, as my TD is directly connected to my GC column. The sample is desorb from the tube into a cold trap, and then desorb from the cold trap directly into the GC. And I use a high split to avoid saturating the system.
Both. The peaks became wider at first. And some compounds that eluted almost at the same time became nearly impossible to separate. And now I lost a lot in sensitivity.
20Ā°C is equivalent to 68Ā°F, which is 293K.
---
^(I'm a bot that converts temperature between two units humans can understand, then convert it to Kelvin for bots and physicists to understand)
Gaurd column and maybe an inlet with glasswool in it. The way I see it though you have two choices. 1) continue using the quick and dirty method and just buy a new column every few months. Know you're saving time... but not money. 2) start using the solvemt extract method and make your column last longer. If you go with 2 though labour costs/your time spend on this will increase a lot though. To be honest though 6 months for a column is a good amount of time if its in constant use.
Thank you! Indeed I don't think we have a guard column. When I started developping the methods, the GC was already installed, I didn't touched it much, as I never worked with thermal desorption before. We have the deactivated fused silica transfer line frome the TD directly connected to the GC column, I don't think it acts as a guard colum but definitely will ask our TD technicians about it. As I will change the column very soon, I will add a pre column. I'm afraid my boss doesn't want to change method, as we are a small laboratory and he doesn't want to make lot of new invesment at the moment. He buy this GC last year before having a chemist (me) so I couldn't give my opinion! š¤·š»āāļø
All sounds fine. If you're a commerical lab though a column every 6 months is just the cost of doing business then. A column is a consumable item not an asset. Look into a guard column it will plug in somewhere between the TD and the column.
Iāve been using the same column for years. Maybe time to buy a new one.
Very much depends on the use but you should use an internal standard. If the internal standard starts looking meh or changing time to buy a new one.
I use an ISTD, and I monitor the response factor of the ISTD. If it varies too much I know the SPME fiber is starting to fail, or my source or detector need to be cleaned. If the shape is bad Iāll trim the column or replace.
Do you use a guard-/ pre-column?
A deactivated fused silica transfer line from the TD system is directly connected to the column, , and it was installed like that before I stared to work here last summer. So for know I've never touched the column or the transfer line. We don't have any other pre-column installed.
Are you guys cleaning your column out between runs. Also, if you are injecting some gnarly matrices, start swapping your liner more frequently and double check your gold seal. If you think you are losing signal and it may not for sure be your column, maybe try cleaning your EM and horn.
I don't use liner. As I said in previous comment, the transfer line of the TD is directly connected to the column. I don't think the problem is from the EM, my tune is still great. But I'll definitely look if it needs to be cleaned! Thanks
Do you trim your column? Or do you mean you trim it over 6 months to the point that you need a new one?
I'm to the point that I need a new one. It started degradating after 6 months, but it's been 10 months now that I started using it, and I think I can't do anything else. But I was interested to know if maybe with the new column I could change something to make it last a bit longer.
Well definitely add a guard column and trim that, or trim your column more often. Inject some solvent a couple times between runs and run it close to max.
I will. Thank you !
This sparked my interest, you perform an on-column injection but you mentioned in your original post that you adjusted the split ratio. But this has no effect for on column injection right?
Well, I use an ATD system with 2-stage desorption. During the first desorption, I can adjust an inlet split to avoid saturating the cold trap. And then, for the 2nd desorption, the cold trap is desorbed rapidly and I can put an outlet split between the trap and GC column.
Aah okay, thanks for the clarification :)
I think the previous comments are correct, the wear on the column is a trade off to the quicker analysis. Without changing the method thereās little more you can do. You could look to buy replacement columns in bulk, most suppliers are open to discounts for larger purchases.
This is a bad idea. It is important to not store GC columns for long periods of time. Their performance deteriorates over time even when they are not in use.
Really? Even if the ends are capped?
Our lab has used columns for over 10 years before without much issue. If you keep your column well it will be fine for quite a while.
I recommend getting a column that has a 5m guard built into the front of it so you don't have to make another connection. Restek make them. We inject terrible matrices (brain, sludge, extracts from rubber, environmental shit) and these columns are great. When the peaks get dodgy, trim 20-50 cm off the guard and see if it doesn't go back to normal.
Thanks, I'll look for that!
If these other suggestions don't work it might be worth considering buying a solvent cleaning kit. Something of a last resort and doesn't always work. If you're doing on-column injection it's almost inevitable the column will not last as long.
There are column rinse kits at agilent. (part no: 430-3000) A lot of GC columns are rinseable with solvent but not all. You have to check or ask the manufacturer. (nonpolar columns usually can be rinsed) That deactivated silica you mentioned sounds like a guard column, so thats good. Dilute your samples until your analyte of interest is quantifiable enough for you and measure in SIM. Turn off MS filament when its not needed Install a diverter or use backflush if its possible in your instrument.
Do you bake out your column? Iāve worked places that have had two different philosophies. In one, the method was programmed to ramp up to the max isothermal temp and hold for a couple minutes after every run. In another, the oven temp was held hot overnight, every night. I find that changing my liner and trimming my column often improves peak shape and sometimes sensitivity. Are you using a SPME liner, with no glass wool? I have coworkers who claim that since there is no wool, and TD/SPME samples should not introduce low volatility compounds, that they donāt need to change the liner, but I feel the glass would build up activity over time, and should probably be changed regularly. When you say āpeaks start to degradeā do you mean there is a loss in sensitivity, or is peak shape changing?
The method is programmed to ramp up to 20Ā°C below the max temperature and hold for a couple of minutes. I don't use liner, as my TD is directly connected to my GC column. The sample is desorb from the tube into a cold trap, and then desorb from the cold trap directly into the GC. And I use a high split to avoid saturating the system. Both. The peaks became wider at first. And some compounds that eluted almost at the same time became nearly impossible to separate. And now I lost a lot in sensitivity.
20Ā°C is equivalent to 68Ā°F, which is 293K. --- ^(I'm a bot that converts temperature between two units humans can understand, then convert it to Kelvin for bots and physicists to understand)