I am using a Waters Q-TOF LC/MS system (uses ESI) and the current settings are set for protein intact mass analysis. How can I use this system to analyze contamination in water or small metabolites/molecules? How can I use MS to detect presence of different salts in the solution?
I read that ESI is good for molecular weights larger than 100 Da. Does that mean I can't detect presence of elements such as Na? What about non-polar molecules?
Sounds like it is time for you to either take a course or two and or buy a book on liquid chromatography mass spec instruments.
I agree with Michael Toner . This analysis must be done by ICP-MS technique.
Hi. You may use other instruments such as ICP-MS, FAAS, ICP-OES for this kind of analysis.
Hey Marcos and Michael, be constructive !
I agree that Daniel should learn some basics, but I'll try to give him some indications.
ESI won't work for observation of elements (metal cations...) except attached to molecules (cationization).
Nevertheless note that anions like perchlorates and similar pollutants were analyzed by ESI.
* Elemental analysis (Na, all metals and some metalloids...) can be done by spectrophotometry (by order of complexity and expenses: Atomic absorption = AA for some, optical ICP for many, ICP-MS for ultra-traces ...)
* Small molecules, metabolites: non-polar contaminants will be better analyzed by extraction and GC/MS. Metabolites are usally more polar and more difficult to extract (in general) and may be ionized in ESI in positive or negative mode (bases and acids respectively), so it may be possible to see them, but the ESI conditions and MS set-up carefully checked.
* Read tutorials on ESI.
Good luck, J-F
Contrary to common wisdom, ESI can be used to detect metal ions if they are present in a solution such as dilute aqueous nitric acid or present as chelated complexes. We did this with an LC/MS system many years ago for a refinery, and I recall a company selling an ESI/MS system several years ago for identifying trace metals in clean room solvents. It is necessary to use a very high cone voltage to break apart clusters and oxides, much as I did with PaperSpray (1,2) and you will need high mass resolving power to separate the inorganic species from organic interferences. That being said, ESI is certainly not a common approach and it is not the method of choice for inorganic analysis. AA, ICP-OES and ICP-MS are widely used and are generally more sensitive and quantitative than ESI for this application.
(1) Cody, R. B.; Dane, A. J. Paper spray ionization for ambient inorganic analysis; Rapid Communications in Mass Spectrometry 2014, 28, 893-898.
(2)Coopersmith, K.; Cody, R. B.; Mannion, J. M.; Hewitt, J. T.; Koby, S. B.; Wellons, M. S. Rapid paper spray mass spectrometry characterization of uranium and exemplar molecular species; Rapid Communications in Mass Spectrometry, 0.
For another reference, please see this article on ESI-MS/MS of metal ions:
https://www.nature.com/articles/srep26785
Robert Cody Jean-François Gal Thank you for patiently explaining that to me. I thought about taking a course but I don't know which ones can explain this to me. Waters for example has many detailed courses but none seems to explain how to change QTOF settings for diffrent pourpuses. And the books that I have explain the theory mostly and are rarely aood for practical purpuses. The instrument availbe to me is a QTOF and I want to learn everything that is commonly done using LC/MS besides peptide mapping and intact mass analysis. It sounds like I need to learn more about ESI potentials. Thank you again!
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