I’ve taken a look at common contamination/clustering ions information. Unfortunately I’m not seeing the main contaminant ions amongst them. The main negative ions are at 233 and 117 m/z in an intensity of 10 to the power of 6 counts per second. Then I also see the following other ions at slightly lower intensities: 391, 375, 359, 299, 263, 250, 233, 221, 217, 212, 179, 141, 117, 97, 73, 59. The 59 ion is acetic acid. Daughter of 117 is 100. Daughters of 233 is 189 and 59. Parents of 233 is 299 and 315.
The main positive ion is 156 at an intensity of 10 to the power of 7 counts per second. Other positive ions at slightly lower intensities are 393, 317, 301, 297, 256, 239, 223, (214, 215), 205, (197, 199, 201), 192, 186, 174, 163, (154, 156, 158, 160), 145, 140, 124, (110, 111, 112, 114), (88, 89.5, 90.5, 91.5), (83, 84, 85), (78, 79, 80), (68, 69, 70), 74, (59, 60, 61). These ions were seen at 5% acetonitrile 0.1% acetic acid. In positive mode the daughters of 156 is 115 and 112 as well as 71 and 73. Parents of 156 is 174 and 197.
LC conditions were as follows: 0.1% acetic acid in water in A and LC-MS grade acetonitrile in B. As stated previously these ions were seen at 5% B at a flow of 0.3 ml/min through a Acquity UPLC BEH C18 (1,7 micrometer, 2.1x100 mm) column. MS conditions were as follows: Capillary at 2 kV, cone at 30 V, desolvation temp. at 600 degrees C, desolvation gas flow at 700 L/hour, cone gas flow at 50 L/hour and source temp. of 130 degrees C. Waters Xevo TQD mass spectrometer.
Recently the system was flushed with 85% acetonitrile and shut down for a few weeks due to electrical power supply problems. When returning I noticed a white powdery precipitate against the window of the source. On opening I saw that the whole source was full of this fine white powder. I've been working on this system for a year and right from the start I was worried about the high background, very bad scanning sensitivity and non-linear responses of all analysed phenols. A colleague of mine had similar problems with only the LC part of the system. He was running phenolic standards on the system using 0.1% formic acid and acetonitrile as mobile phases and doing only UV detection. He once had to flush the system with 60% acetonitrile before going on leave. When he returned the flow cell was blocked by a white insoluble powder. I've noticed that mass 233 increases tremendously when flushing with higher concentrations of acetonitrile. I've also noticed that when I return after a weekend during which the system was standing with 85% acetonitrile in it the 233 mass was very prominent in the background and as I flushed the system this mass decreased so that 117 becomes the dominant background ion. I get the impression that something is leaching from a part in the system, especially at high acetonitrile, but 117 is coming off the LC system all the time, no matter what the acetonitrile concentration is.
I have also attached some background spectra.
Good day!
Look the attached file, I hope it will help you!
Best regards,
Azamat
Hello Amazat,
Thank you for the list. I made a copy for using here in the lab.
Best regards,
Gerrit
What is the source of your water? I would suspect either the water, acetonitrile, or acetic acid is the source of your white powder. Try new sources for each to see if the contaminant goes away.
Thank you so much for your replies. I have taken the precipitated white powder for chemical analysis on an x-ray fluorescence scanning electron microscope and it was found to be magnesium oxide. The powder is insoluble in most solvents. I have also sent some samples for ICP-MS to confirm the XRF results. Along with the powder I also submitted some of our MilliQ water as well as the acetonitrile we use. My initial tests on the water and acetonitrile was ambiguous. I saw a lot of background peaks when infusing LC-MS grade methanol, but later found out that someone had contaminated the solvent with plasticizer shortly after installation and most probably several more times afterwards as well (needless to say I am not impressed). I do not trust the infusion valve any more, because it might be contaminated by several previous "contaminations". I will first need to prove this is absolutely clean before I can use it to test the cleanliness of solvents. However, when doing tunings using water and acetonitrile I do not see major contaminants interfering with the tuning. So my initial tests showed that these solvents are clean, but I still would like to confirm this by ICP-MS.
I am flabbergasted as to where this Magnesium contamination could be coming from. We use the same mobile phases on all our other LC instruments and have never seen such precipitation problems there. I have been using HPLC for many years using lower purity solvents and have never seen this happening. The sampling cone is heavily contaminated. It looks like when someone had been running phosphate buffers for an extended time. The white powder is lying, literally in small heaps, at the bottom of the source enclosure. It is clear that the contamination had been pushed in through the capillary coming from the LC side, because the top part of the source is much cleaner.
If the ICP-MS confirms that our solvents are clean, my best approach now would be to isolate parts of the system and check for contamination levels.
Hi Manda,
Quite often we see peaks corresponding to cluster ions that contain metal ions (in particular iron ion) when we start the hplc. Regarding your question above, I'm sure that the main negative ion at m/z 233 is for [Fe(OAc)3]- that forms ion m/z 315 after addition of two ACN (82 mass units). Ion m/z 233 may lose CO2 to give ion m/z189. The main positive ion at m/z 156 corresponds to [FeOAc(ACN)]+ that gives rise to ion m/z 174 and m/z 197 after addition of water and ACN respectively. Ion m/z 156 loses ACN to give [FeOAc]+ at m/z115, which in turn yields ion m/z73 [FeOH]+ after loss of CH2CO.
Hi Yinrong Lu
Thank you for the information you provided concerning the possible identity of the main cluster ions I'm seeing. What is interesting is that we notice some rust stains on the binary solvent manager mixer and it seems to become worse over time. I have attached a photo of this for you. This might be why we are seeing these huge levels of Fe contamination on our system. I think this mixer is supposed to be made of stainless steel, but a quick handheld XRF analysis revealed that it contains too high Fe levels. So, it seems to be made of a lower grade of stainless steel which is vulnerable to rust.
Most probably the major 117 ion I see in negative ionisation is a cluster from MgOH then. I'm zooming in on the source of this as well. I see some white precipitate under the syringe valve and I'm waiting to hear from Waters about the chemical composition of the parts of the syringe valve. If I apply your information about Fe-acetate adducts to MgOH then an adduct of MgOH with acetate would have a mass of exactly 117.34210 and a loss of -OH would yield a mass of 100.34016 which is in agreement with the daughter ions I see in negative for the 117 ion. I suspect the MgO (very insoluble) would not be in solution all the time but precipitates out from the more soluble MgOH when eluent dries in spaces within the LC. Does my reasoning about these MgOH adducts make sense?
Your input is highly appreciated.
Manda
Hi Manda,
Your strategy to deduce a possible formula for the major ion at m/z 117 in the -ve mode is right, but it's unlikely in this case that [Mg(OH)2OAc]- be the right candidate for this ion. Firstly, loss of OH- is impossible to leave a neutral salt [MgOHOAc] to be detected in MS; secondly, my experiment to infuse Mg(OH)2 solution in ACN/H2O/AcOH (ca 50:50:2) shows major ion at m/z 201 in the -ve electrospray mode mass spectrum, which is in agreement with the expected [Mg(OAc)3]- ion. It produces product ions of m/z 201, 159, 157, 115, 113, 89 and 59 and the fragmentation can be well interpreted.
Based on what you described, the ion of m/z 100 could be [AcO+ACN]-. Ion of m/z 117 could be a product ion of a ion with larger mass after loss of a neutral molecule. If the white precipitate could be proven to be ammonium acetate, then the ion at m/z 117 could be [AcO+ACN+NH3]-. Ion 117 was indeed detected as very weak peak in my QTof system when ammonium acetate solution was infused, Its formation was favored at higher cone voltage, say 50, and its fragmentation does give a single product ion at m/z 100. However the work is not conclusive.
This is what I thought and observed. More work needs to be done to find out what the ion m/z 117 actually is.
Hi Yinrong Lu
Thank you very much for your answer and for the tests you did to help. The white powder has been identified as MgO. I however suspect that it is leaching from the system in another form and then crystallizes as MgO at a later stage, because MgO is not very soluble. So, I have decided to take eluent that have passed through the entire LC system for ICP-MS analysis and compare that to eluent that have not passed through the LC system. That way I would know which main ions to expect in the LC-MS.
There is some of this powder lying underneath the sample syringe valve (not around the rheodyne valve though). We have confirmed that this powder is also a magnesium powder. Another interesting phenomenon is that I see white crystallization in grooves on the outside of the sample syringe valve. There has been no leak there in that position. So, these crystals seem to be growing right out of the plastic. Waters sent me information on this valve that indicates it is made of 20% PTFE filled Peek. I can't explain any of this. Later I will attach a photo of this crystallization as well.
Thanks a lot,
Manda
Attached is a photo of the weird crystallization forming inside engraving on the outside of the sample syringe valve.
I'd like to confirm that the white crystals visible inside the engraving on the outside of the sample syringe valve is indeed also magnesium oxide. I tested (by XRF) some of the plastic that the valve is made of (20% PTFE filled PEEK) to see if it contains magnesium oxide and it doesn't. It seems that somehow the magnesium oxide has diffused from the inside of the valve to the outside. Otherwise there was a liquid leak from above and some of the fluid was left behind in the engraving. I however never saw any liquid leaking onto that engraving on the outside of the valve. This sample syringe valve seems to be the heart of the problem. I just don't understand how the magnesium oxide can move from this low pressure part of the system into the high pressure flow path. I am detecting magnesium oxide in the eluent coming from the system right at the end of the flow path after the UV detector. If anyone has any ideas it would help a lot. At the moment I'm also collecting eluent coming from the system just after the injection valve, but before the column. I'm sure the main magnesium oxide source lies in the injection system.
212 peak in negative is very common, it could be 212.07507 [M-H]- C10H15NO2S n-butyl benzenesulfonamide A, K which you can find also at 214 in positive. look at the attached list
Did you get to the bottom of this Manda? I have a background of e6-7 counts of m/z=117 in ESI+ mode when running water through the pumps and lines. It disappears when I stop the flow into the ESI probe and then 149 becomes the most dominant peak. I have used acetic acid in my solvents.
Hi Babak, I also used acetic acid as modifier and 117 is the main background ion I see after rinsing the system extensively with mixtures of water and acetonitrile containing 0.1% acetic acid. I have found a paper that describes the ions one can typically expect to find with acetic acid modifier and 117 does not seem to be one of them. I suspect that the acetic acid does form an adduct with another contaminant leaching from the system. I have not completely solved this problem. However, I have proof that the Waters solvent inlet filters (stainless steel) was contaminated and leached several metal ions including magnesium, calcium and aluminium. This is true for brand new filters and even after several sonications these filters still leach contaminants. Since I replaced these filters with Agilent glass filters the background seems to be lower and there is better sensitivity for the compounds we'd like to analyse including polyphenols. I do however suspect that other Waters parts may contain contamination as well. Which solvent inlet filters have you been using on which system? Do you use water and acetonitrile as mobile phase A and B respectively and what is the concentration of your acetic acid? I tested the mobile phases as well as the LC-MS grade acetic acid by ICP-MS and they are very clean and contain minimal quantities of metal ions. However, I saw major amounts of metal ions and even some other organic components leaching from those filters. The chemical inertness of the system is suspect and I have spent 3 years trying to find where the problem lies.
Yes, I use water as A and then ramp up to ACN (B). I' use 0.5%acetic acid (the acetic acid is 99% glacial).
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