How to clean Agilent 1290 / 6495 system from pesticides

[TLC84]

The title is ambitious, probably. I have a situation: In January 2021 I was transferred to this equipment, because former analyst left a job that month. The problem is that in the past year this machine was heavily used in pesticides analysis, and now it is just impossible to get rid of several pesticides: foramsulfuron, fenuron, bifenazate, nicosulfuron, imazalil, and several others. I tried almost anything to clean the system. I have cleaned capillary and it goes well with autotune. Cleaned column with any variant described in literature. Cleaned system with warm water (70 - 80 C) without column and flow 5 mL/min. Many other things, but those guys just stays in chromatogram. It is indicative, and you can see in TIC picture, that my problems are strict between 4 and 5th min, there are just a few latter on. Please help

[James_Ball]

The title is ambitious, probably. I have a situation: In January 2021 I was transferred to this equipment, because former analyst left a job that month. The problem is that in the past year this machine was heavily used in pesticides analysis, and now it is just impossible to get rid of several pesticides: foramsulfuron, fenuron, bifenazate, nicosulfuron, imazalil, and several others. I tried almost anything to clean the system. I have cleaned capillary and it goes well with autotune. Cleaned column with any variant described in literature. Cleaned system with warm water (70 - 80 C) without column and flow 5 mL/min. Many other things, but those guys just stays in chromatogram. It is indicative, and you can see in TIC picture, that my problems are strict between 4 and 5th min, there are just a few latter on. Please help

I can't open the images here at work, but if these are making defined peaks then it means the contamination is prior to the column, or the column itself. If you use another column do you get the same contaminates showing up?

If yes, then from the needle to the column would be the problem. I just started using a similar instrument so I am not completely familiar with them yet, but it sounds like maybe the rotor of the switching valve in the autosampler could be contaminated and needs to be replaced.

[TLC84]

If you use another column do you get the same contaminates showing up?

Thanks @James_Ball for fast reply. Yes, I have borrowed identical UHPLC column (Zorbax C18, but cannot recall exact model from memory here at home), and same problem was there. Initially, I thought that my former colleague overkill column with pesticides. She played at insane concentrations of pesticides standards at ppm levels. So I have had cleaning the column indefinitely with all combinations of solvents compatible with column. Then I thought, OK, it must be the ion source, so I cleaned capillary, but obviously that didn't solve anything.

Today I have found something interesting. Someone responded to similar question at ResearchGate that he had superb results cleaning similar problem with 10 - 20 times diluted bleach solution, with approx 20 column volumes. Is that a viable option, anyone really tried it besides him?

[James_Ball]

Have you tried pumping 100% Methanol or Isopropanol through the system overnight?

Looking at the solubility, these are almost insoluble in water but very soluble in alcohols. I would remove the column, and just pump alcohol through the system going directly into a waste container over night and see if that helps. You will probably want to do flush in both "bypass" and "mainpass" of the autosampler valve to make sure you flush both paths. I would do that before using bleach because I don't know how bleach will affect the material of the valve rotor.

[TLC84]

Have you tried pumping 100% Methanol or Isopropanol through the system overnight?

Thanks! I tried isopropanol, that was the very first attempt, when I thought it was column the problem. But, then again, I'm not sure that I ever tried flush with solvents without column... Hm, I'm now at the lab, but the instrument is heavily occupied with some cannabinoids in cosmetics samples, tomorrow I'll flush my entire shift, and I'm here 12h a day since relocated to this lab . Without column, with methanol, skipping MS unit, and everything else as you suggested.

[H.Thomas]

Hi, just one easy thing you could try: when I had problems with pesticide blanks on a similar system (6470), it helped to change the capillary from the column to MS, and also the one from the swithcing valve to the ESI. Especially PEEK-capillaries seem to adsorb some pesticides.

[lmh]

.. and since it runs as a nice peak, autosampler contamination is a big possibility. Make sure your needle wash is appropriate for washing off the target compounds. If they're really hydrophobic, use a highly hydrophobic needle wash, and run a whole load of very short runs in high organic solvent from the pump, so you wash out the needle and injection valve really thoroughly. A possible plan is to run one normal blank, run 20 or 30 2-min runs at 100% organic, and then a couple of normal blanks, and see if the peak is getting any smaller. If it is, carry on. Sometimes, with some contaminations, it's worth zipping backwards and forwards between high organic and highly aqueous, but for true hydrophobes, lots of organic should help.

[TLC84]

Thanks guys! However, I haven't moved much farther, besides my personal opinion that there is something fishy with entire system Seriously now, I flushed system with hot water, collected efluent and then prepared with SPE like pesticides in water analysis, then analyzed on the 1200 / 6410 QQQ system, the system routinely used for pesticides in water analysis, and there was nothing at all. I have expected mere qualitative peaks, just a sign that something leaks from somewhere, but nothing. Then I have changed current method on the 6495 from dMRM to MRM and used only foramsulfuron transitions and parameters from the Agilent pesticides database. There are other bodies, but foramsulfuron is the most persistent one I think. The sample is blank - methanol, and the spectrum is unsolved mystery.
After tons of cleaning with all yours suggestions in minds, I think that there is less foramsulfuron then last week, but he is still there after all. The institute asked service about this, and they just replied that we should clean better, or something in that manner.

[James_Ball]

The big problem with the 6495 versus the 6410 is how much more sensitive it is. Every little amount of contamination is going to appear on the 6495. The question becomes, how low do you need to go? If your lowest calibrator can be 10x the carryover amount then it may not be a problem at all.

[TLC84]

Cannot more agree with you, the 6495 is super sensitive MS/MS, I was so excited when I started working with him in Dec 2020. However, it's perfection causes limitations in analytical lab when routinely dealing with multiresidue methods. Leftovers at system level are just disturbing. It could be easy to ignore if they are as constant noise, but it's more like random generator... The chrom comparison below shows segment of 30 short runs with 100% ACN. The most abounded peak is, you guessing, foramsulfuron.