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- Posts: 13
- Joined: Mon Nov 24, 2014 3:17 pm
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. So, it seems that Waters is once again not willing to truly help. As you can imagine this is a 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.
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.
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. So, it seems that Waters is once again not willing to truly help. As you can imagine this is a 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.
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.
