Ghost contamination in UPLC-TQD
Comments
-
Please supply method, this seems to be a sticky compound and/or if there is a solubility issue, you will keep re-contaminating the system. I will ask around concerning the nature of these compunds, but in the meantime please send details on the gradient, sample diluent, weak needlewash and injection mode and we can make recommendations.
Best regards,
Liz
0 -
Dear Liz
Normally for screening we extract samples in high organic and diluted for injection in high aqueous (10-25% MeOH),
Please find attached Waters STA SOP_2 that we working with
regards,
Salman
0 -
Hello
I am sorry that there is a deadline. With CO we have to decontaminate first and so I have attached a contamination guidance document. You need to wash out the system to get rid of these peaks. It is very disappointing that you are still seeing the peaks, but absolutely the system can hold up peaks and then gradually elute them, especially if a high concentration was introduced into the system. However, you know this happened in one instance so it tends to infer that the sample is located somewhere and can be eliminated. I am going to go through the areas that need to be checked. I do suspect the loop or the needle or the wash station. If these parts and terms are unfamiliar work with you, your local service representative should be contacted and and then let him walk you through the process of elimination.
As this is an old method and now you are seeing carryover, you should troubleshoot one thing at a time. However, please remember to learn from this experience. You know that the contamination came from a sample – that sample was there anything different about it, think about the differences so you can avoid issues again. What changes occurred between last carryover free analysis and current? Any change in method conditions (diluent, LC parameters etc.) occurred between last carryover free analysis and current? I am going to suggest that you loaded too much sample. It seems to me that is possible as you indicated that usually you usually run a 10 uL loop and went to a 20 uL loop.
And because you told me two things were changed, we will start there. You changed the loop and the needle. My suspicion is an improperly swaged loop or needle or failing that there is compound left somewhere else unaccounted for.
First, try reseating the loop only. Does that help? I suggest this as I also note the peak in the 20 uL loop has a poorer peak shape than earlier.
Also check the ports of the injector and wash station should be flushed. Use a clean syringe. Does this help?
Also the volume detection device should be checked. This will be in question if in FL or PLPA injection modes there is no carryover, but there is in PLNO injection mode.
Also I think that as you changed the needle you should inspect the connections are properly swaged to injector valve. Does this help?
Also inspect the pre-piercing needle, is it dirty, flush or exchange. Does this help?
Inspect and clean the BOS line. Does this help?
Wash station block should be checked and the port O-ring should be inspected or replaced for material build up. Does this help?
If this does not help then the injector pod needs to be replaced.
I hope the following document assists, check which type of contamination applies and use the wash porcedure. But as I say, if this is unfamiliar please let a FSE from Waters assist locally.
0 -
Dear Liz,
Thanks for detailed explanations, i told you that we have very strict schedule to clean the system end of the day, bcuz we have daily different types of samples and some time it is difficult to predict the concentrations...
as i told you i will try Acid wash so i did next day,,,,
first we replaced the injector POD wash all line/loop/needle by 50/50 MeOH:water with prime & flow, then inject the blank, still same contamination there.. then we replaced new sample loop and wash all line/loop/needle by 50/50 MeOH:water with prime & flow, , then inject the blank, still same contamination there, but at this time intensity was low (as per S/N), then we replaced pump outlet and column inlet/outlet, wash all by 50/50 MeOH:water with prime & flow and inject the blank, still contamination but very low intensity.
After that we decided to wash UPLC by 20% phosphoric acid,according to “Routine UPLC cleaning procedure” we injected the blank…… ‘NO CONTAMINATION’ of m/z 280, 319….
This means something stuck inside the BSM not Sample manager.... i think we need service because more than one year no PM visit.. UPLC needs some refreshments... "i am suspecting inlet filter of primary pumps tired & one year old and holding and hiding samples.........."
regards,
Salman
0 -
Oh dear, it was the pump, no assumptions should be made in troublehooting. You can get a PM kit for each instrument, but an annual PM is recommended. Thank you for letting us know.
BR
Liz
0
