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On‐surface Fenton and Fenton‐like reactions appraised by paper spray ionization mass spectrometry
Author(s) -
Resende S.F.,
Oliveira B.S.,
Augusti R.
Publication year - 2018
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/jms.4252
Subject(s) - chemistry , radical , hydroxyl radical , yield (engineering) , mass spectrometry , protonation , substrate (aquarium) , ion , photochemistry , inorganic chemistry , organic chemistry , chromatography , materials science , oceanography , geology , metallurgy
On‐surface degradation of sildenafil (an adequate substrate as it contains assorted functional groups in its structure) promoted by the Fenton (Fe 2+ /H 2 O 2 ) and Fenton‐like (M n+ /H 2 O 2 ; M n+ = Fe 3+ , Co 2+ , Cu 2+ , Mn 2+ ) systems was investigated by using paper spray ionization mass spectrometry (PS‐MS). The performance of each system was compared by measuring the ratio between the relative intensities of the ions of m/z 475 (protonated sildenafil) and m/z 235 (protonated lidocaine, used as a convenient internal standard and added to the paper just before the PS‐MS analyzes). The results indicated the following order in the rates of such reactions: Fe 2+ /H 2 O 2 ≫ H 2 O 2 ≫ Cu 2+ /H 2 O 2 > M n+ /H 2 O 2 (M n+ = Fe 3+ , Co 2+ , Mn 2+ ) ~ M n+ (M n+ = Fe 2+ , Fe 3+ , Co 2+ , Cu 2+ , Mn 2 ). The superior capability of Fe 2+ /H 2 O 2 in causing the degradation of sildenafil indicates that Fe 2+ efficiently decomposes H 2 O 2 to yield hydroxyl radicals, quite reactive species that cause the substrate oxidation. The results also indicate that H 2 O 2 can spontaneously decompose likely to yield hydroxyl radicals, although in a much smaller extension than the Fenton system. This effect, however, is strongly inhibited by the presence of the other cations, ie, Fe 3+ , Co 2+ , Cu 2+ , and Mn 2+ . A unique oxidation by‐product was detected in the reaction between Fe 2+ /H 2 O 2 with sildenafil, and a possible structure for it was proposed based on the MS/MS data. The on‐surface reaction of other substrates (trimethoprim and tamoxifen) with the Fenton system was also investigated. In conclusion, PS‐MS shows to be a convenient platform to promptly monitor on‐surface oxidation reactions.