I would like to ask some more questions about a problem I described previously on this forum. I started working on the Acquity Xevo TQD system more than a year ago in April 2014. Immediately it was obvious that there was a high background and very low scanning sensitivity. I could not see phenolic compounds such as catechin and caffeic acid at concentrations below 5 mg/L at a 5 microliter injection volume in fullscan. Waters says they are not able to provide me with specifications for the fullscan functionality of the Xevo-TQD or with specifications for normal background. Another symptom I noticed was non-linear standard curves of all 18 analysed phenolic compounds in MRM mode as well as inaccurate quantification at levels above the limit of quantification. Please note that this is for the standards on their own. There was no matrix effect from samples involved in this phenomenon. The standard curves are non-linear at both the low and high end of the curves. I argued that these symptoms might indicate that some form of ion suppression is influencing the data. The residuals for the calibrations also showed a clear pattern and was certainly not random.
During 2014 Waters did a decontamination on the system, but this did not make any difference to the situation. They also did a manual tuning by remote login of a UK engineer which improved the negative ionisation sensitivity considerably. However, positive ionisation sensitivity still seems to be very bad. What bothers me about this scenario is that do I need to now always get a remote login from the UK to see any peaks in fullscan whatsoever, what would be the effect on resolution (there is always a balance between resolution and sensitivity on mass specs)? I have spoken to other triple quadrupole users of Agilent systems. They have no problems with fullscan ability after just a autotune. I have also found scientific papers where QQQ instruments were successfully used to screen in fullscan at ug/L levels. Apart from the decontamination that was done Waters (and their agent Microsep) have mostly denied the existence of any problem and said that I only needed further training.
In January 2015 a large amount of white powder was discovered in the source which has since been identified as magnesium oxide. Following this discovery I did some leaching experiments on the system and found that magnesium oxide, iron oxide, silicon oxide, sulphur and calcium was leaching from the LC system on its own. All our mobile phases were tested as well and were found to be clean.
Waters have since indicated that they are willing to exchange the entire flow-path of the LC. I am open to this idea. However, I am very concerned that damage might already have been done to the MS due to the metal ion contamination that have entered it for a year and especially after the large amount of MgO that landed in it in January. I wrote a letter to Waters explaining my concerns and asking for a commitment from them to repair the MS if there were any damage. I did not get a reply from them for 3 weeks and last week my boss told me that they want to speak to him alone. Clearly the local Waters representatives see me as a threat. As you can imagine this is an utter nightmare for me. I am willing to work with them to get things fixed but obviously I need to make sure that we do address the possibility of damage to the MS. I have spoken to engineers and people who are experienced in the possible repercussions of this kind of contamination ending in a MS. They agree that the possibility of electronic damage to the MS is there due to the possibility of short-circuits. I'm not sure what will be said in that meeting with my boss but I am sure it will not be good for me even though I have been working so very hard to get to the bottom of this problem. I have since found out that it is the local Waters representatives who wanted this private meeting. Waters International was not aware of this.
There are so many questions I could ask. I will start with the most important one.
Would you be worried about the MS too...?
Would you be content with that poor fullscan sensitivity and with not being able to test what you are seeing against specifications? (MRM specifications are of no use in such a situation, because the selectivity of the QQQ enables it to pass all MRM specifications even while loads of contamination is entering it.)
In case you would like some more detail about the analytical method:
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. Acquity I-class.
I suspect the magnesium oxide contamination was present right from the start. Shortly after installation the UV flowcell was blocked by a white insoluble powder. We do not do metal ion quantifications. We analyse apple juice.
I am sorry to hear that you are experiencing some issues like this. Normally it is very difficult to provide a background level specification, because the background is dependent on so many factors.
The good news is that contamination of this sort is rare based on my experience.
You may want ask to have a full HPLC system passivation process run if possible to ensure that you have no residual metal contamination present in your system. This is a process of washing with Nitric acid, followed by water, followed by IPA, then water before returning to your normal mobile phase. This must be done without your HPLC connected to the MS system. Following this I would also recommend a good source clean for your MS system.
There is unlikely to be lasting impact on your MS system and you should recover full operating performance once this cycle is completed.
If the problem occurs again after this, then I would look at external sources for the introduction of the contamination.
Wishing you the best of luck and success.
Hi there
I have some experience with triple quadrupole instruments although not on the new Xevo models from Waters. the instrument I used to work was a Quattro LC from Micromass, the company Waters bought to start their line of triple quads. I have experienced a similar situation with low full scan sensitivity, but with MRM sensitivity preserved. In our case the problem was solved when, because of an unrelated issue, the power source of the quadrupoles was replaced. In your case I would want an engineer from Waters to service the instrument and run some of your samples to see if they can meet at least minimum performance. If 5mg/mL is your LOD you would be better off with an HPLC with DAD than with your triple quadrupole MS. I would be very surprised if the instrument was indeed damaged since if so, you would probably not detect anything even at high concentrations, but it is quite possible that metal deposits on the ion beam path is responsible for your low sensitivity. I hope this helps somehow. Good luck!
Thank you for your reply, Eduardo. Could you please indicate how low concentration one should be able to do fullscan on a triple-quadrupole MS. I realize that this will differ from application to application but what are you able to do after the power source replacement?
I need to clarify that the low sensitivity was seen before the MgO was found in the source. Since the MgO was found the instrument has not been on due to the possibility of electronic damage that could occur with the MgO still in the MS. We first need the vendor to do a thorough cleaning. Then only will we be able to see if there was any damage.
Hi Manda...I cannot give you a precise Figure, but I remember preparing my extract stock solutions at 1mg/mL and injecting (20 microliters) at 0,5 mg/mL. This was for analysing a complex crude plant extract. Standards should easily be analysed at 50 ng/mL levels at full scan with the signal processed using extracted ion chromatograms. Good luck!
I am sorry to hear that you are experiencing some issues like this. Normally it is very difficult to provide a background level specification, because the background is dependent on so many factors.
The good news is that contamination of this sort is rare based on my experience.
You may want ask to have a full HPLC system passivation process run if possible to ensure that you have no residual metal contamination present in your system. This is a process of washing with Nitric acid, followed by water, followed by IPA, then water before returning to your normal mobile phase. This must be done without your HPLC connected to the MS system. Following this I would also recommend a good source clean for your MS system.
There is unlikely to be lasting impact on your MS system and you should recover full operating performance once this cycle is completed.
If the problem occurs again after this, then I would look at external sources for the introduction of the contamination.
Wishing you the best of luck and success.
Thank you Mark. This is encouraging. The service provider is planning on doing such a passivation and source clean soon. What is interesting is that it seems that several metal ion surfaces have been oxidized, because it is always the metal oxides we see leaching from different parts of the system and it is not always the same metal oxide. That makes me think that a strong oxidizing agent might have been put through the entire system and damaged the metal. We don't work with such agents at all on the system and we have had problems right from the start. I wonder if something might have gone wrong in the original passivation process before or at installation.
Thank you Eduardo for the information. You don't perhaps know of a scientific publication where typical fullscan sensitivity for phenols using single or triple quad is referred to?
Manda...I found this paper, but it doesn´t state the injection volume. However, fractions were injected at 1mg/mL for full scan experiments and TI count is around 10^7:
https://www.researchgate.net/profile/Jaume_Bastida/publication/7924526_Qualitative_analysis_of_phenolic_compounds_in_apple_pomace_using_liquid_chromatography_coupled_to_mass_spectrometry_in_tandem_mode/links/0deec51f775b51816a000000.pdf
I also think this one might be useful:
http://onlinelibrary.wiley.com/doi/10.1002/rcm.1697/abstract
Article Qualitative analysis of phenolic compounds in apple pomace u...
Hi All, 15 mcl.
Work was done with regular LC (low pressure) and an API3000 system from Applied Biosystems, now SCIEX.
I don´t want to comment anything about your issues with your current system, as I´m working for one of the Waters competitors.
Good luck.
Thank you Eduardo and Ferran. This is going to help me a lot because it is even nearly the same application we are looking at. I'm analysing apple juice and apple concentrate. Will definitely have a closer look.
I would also like to know whether autotuning of the mass spec is normally sufficient in order to get the sensitivity as seen by Ferran, Eduardo and others or would you need to do a special manual tuning to get to these levels? I've spoken to researchers working in the wine phenolics field and according to their experience an autotune should be sufficient to get good sensitivity.
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