-
- Posts: 6
- Joined: Wed Feb 12, 2025 9:37 pm
Having problems with consumables lately. Please let me know if you have any insights or troubleshooting steps. Drugs of abuse testing.
Agilent LPD Tapered Glass Wool Liners (5190-2275):
Old Lot: All 100 of them worked great with long lifetimes.
New Lot: High fatty acids, low-to-no morphine response (see image).
Apparently fatty acids can come from hand oils or cream that leach through gloves, and when hand-rolling glass wool these fatty acids can incorporate into them. Hence why not every liner is bad in the lot. Wild. For this to happen suddenly to multiple analysts and across several different GC systems suggests the issue comes from manufacturing. To avoid this, finding a liner that deactivates the wool and liner at the same time is crucial. The Ultra Inert or Topaz deactivation lines do this, but sadly neither work with our methods as it obliterates chromatography of the amphetamines (below). Could be a temperature or pressure programming problem, but not looking to adapt methods to the liner.
While the source of fatty acids and how to remove them (heat, ipa) makes sense, I am not too sure how or why this would affect the morphine response, or where it's going honestly as carry over or ghost peaks of morphine never arise. It also affects vardenafil. These two molecules have -OH groups in common that the other standards don't. Something to do with that? Has anyone come across this problem and know of any solutions? Changing liners is an option of course, but see the next section for different problems.
Restek Siltek LPD Tapered Glass Wool Liners (21033-213):
I thought perhaps since the the system is new, there is less contamination/active sites but even cleaning the split vent and inlet doesn't really help. Is there something else that could be causing inlet discrimination of the amphetamines? I know the salts are notoriously known to be challenging to chromatograph due to difference in boiling points of the free base/salt forms but clearly it can be done with the current method and consumables used. Do split valves or other inlet mechanical parts degrade over time? Keep in mind many of these instruments are at most 5-10 years old, and the ones that have the most issues with broadening aren't the oldest. The broadening occurs on every GC other than the new one, although some more so than others. Broadening will sometimes spontaneously resolve itself without intervention. Perhaps just the right combination of samples that go through it. Would like to identify why and speed this process up.
Thank you!
Agilent LPD Tapered Glass Wool Liners (5190-2275):
Old Lot: All 100 of them worked great with long lifetimes.
New Lot: High fatty acids, low-to-no morphine response (see image).
- Heat conditioning/IPA washes help to remove the fatty acids but doesn't always fully recover morphine response.
- High levels of fatty acids (stearic/palmitic) even in a no injection/instrument blank run.
- Re-installing the used liner from the old lot shows immediate restoration of morphine and no fatty acids (indicating this new lot is the issue).
Apparently fatty acids can come from hand oils or cream that leach through gloves, and when hand-rolling glass wool these fatty acids can incorporate into them. Hence why not every liner is bad in the lot. Wild. For this to happen suddenly to multiple analysts and across several different GC systems suggests the issue comes from manufacturing. To avoid this, finding a liner that deactivates the wool and liner at the same time is crucial. The Ultra Inert or Topaz deactivation lines do this, but sadly neither work with our methods as it obliterates chromatography of the amphetamines (below). Could be a temperature or pressure programming problem, but not looking to adapt methods to the liner.
While the source of fatty acids and how to remove them (heat, ipa) makes sense, I am not too sure how or why this would affect the morphine response, or where it's going honestly as carry over or ghost peaks of morphine never arise. It also affects vardenafil. These two molecules have -OH groups in common that the other standards don't. Something to do with that? Has anyone come across this problem and know of any solutions? Changing liners is an option of course, but see the next section for different problems.
Restek Siltek LPD Tapered Glass Wool Liners (21033-213):
- Good, but prone to amphetamine peak broadening (below)
- amphetamine (primarily meth) peak broadening can occur as early as the next day
- An injection of a weak solution of sodium bicarb in MeOH temporarily corrects it, but this isn't reliable long term of course and can cause minor breakdown of other compounds in the mixture. Can something else be used to condition the liner?
- I am not entirely certain the liners are 100% to blame as on our brand new 8890 GCFID, this liner was used for 4 months (honestly could have gone longer) and peak broadening was never observed. For reference, the GCMSs often need to replace liners every 2-4 weeks, and GCFIDs 4-8 weeks.
I thought perhaps since the the system is new, there is less contamination/active sites but even cleaning the split vent and inlet doesn't really help. Is there something else that could be causing inlet discrimination of the amphetamines? I know the salts are notoriously known to be challenging to chromatograph due to difference in boiling points of the free base/salt forms but clearly it can be done with the current method and consumables used. Do split valves or other inlet mechanical parts degrade over time? Keep in mind many of these instruments are at most 5-10 years old, and the ones that have the most issues with broadening aren't the oldest. The broadening occurs on every GC other than the new one, although some more so than others. Broadening will sometimes spontaneously resolve itself without intervention. Perhaps just the right combination of samples that go through it. Would like to identify why and speed this process up.
Thank you!
