Dear MS community,
I am working with a RapidFire400 ESI-QTOF System and I am facing problems with PEG and Phthalate contaminations that cause ion suppression drastically decreasing my protein signals.
In order to minimize potential sources of contamination, I am so for only using 1 pump of the RapidFire400 system and directly inject 100% LC-MS grade ACN into the nebulizer of the ESI-QTOF at 1 mL/min. However, even several hours of washing do not help to decrease the signal of the contaminations, which indicates a systemic source.
In my opinion, potential sources of contamination could be:
1. The solvent, whereas I need to admit that I do not use air filters on my solvent bottle caps so far Can somebody please recommend MS-compatible solvent air filters?
2. Pump components (tubings, valves), which hopefully is unlikely, because the vendor built the system exactly for Q-TOF MS applications
3. Nitrogen gas (tubings, filters) > is this possible at all?
4. Mass spectrometer itself (spray chamber, shield, cap, transfer capillary) > regularly cleaned.
Could you please comment on the most likely sources of contamination.
Thanky you very much in advance for your input.
Phthalates may be found as plasticizer for plastic bottles (PE, etc.), check if your solvent was stocked in such PE bottles. Phthalates are not very volatiles, so I dont think that air could be the contamination source. For PEG, there are many possible sources, but not usually in contact with HPLC components. The other sources are unlikely, except a big accidental contamination of tubing.
Thank you very much for your input. We are not using any plastic bottles, which is why I am struggeling.
Did anybody by chance come across 130.1597 m/z in 100% ACN or mixtures of for instance 50% water / 50% ACN, 0.1%FA? Cannot find this mass in any literature
It seems that your ion is listed in the attached document and its source.
The contaminant is unusual
130,15903 [M+H]+ C8H19N DIPEA Diisopropylethylamine, solvent
I added also a more general article on MS contamination.
Good luck!
J-F
Dear Prof. Gal,
thank you very much for your answer. I need to admit that I saw DIPEA in several lists (sorry for not mentioning before), but our MS or our probes never saw the compound at any point. I therefore heavily doubt that it is related to that solvent. Any other suggestions?
It may be a Na+ adduct (or similar adduct) but I don't see a composition compatible with the exact mass.
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