研究目的
To investigate the paradoxical relation between the secondary emission mass spectra of Methylene Blue and its leuco form, and to propose an explanation for the observed redox reactions under mass spectrometric conditions.
研究成果
The study concludes that redox reactions under secondary emission mass spectrometry conditions proceed in the direction permitted for the initial form of the redox-active compound, leading to paradoxical mass spectra where the oxidized form appears reduced and vice versa. This finding is crucial for correct identification and simulation of redox reactions in such systems.
研究不足
The instability of leuco Methylene Blue in pure form hinders mass spectrometric analysis, and the redox reactions are influenced by the matrix and ionizing conditions, which may not fully represent all environmental factors.
1：Experimental Design and Method Selection:
The study used fast atom bombardment (FAB) mass spectrometry in the positive ion mode to analyze mass spectra of Methylene Blue and its leuco form. The rationale was to observe redox reactions induced by ionizing factors.
2：Sample Selection and Data Sources:
Leuco Methylene Blue was synthesized by mixing equal volumes of
3：2 M cysteine and 03 M Methylene Blue aqueous solutions, followed by drying and dissolution in matrix materials. The completion of the redox reaction was monitored spectrophotometrically. List of Experimental Equipment and Materials:
An MI-1201E sector magnetic mass spectrometer (SELMI, Sumy, Ukraine) was used with argon as the bombarding gas (
4：0 keV energy). Glycerol (99%, Sigma, Germany) and nitrobenzyl alcohol (5%, Fluka, Switzerland) served as liquid matrices. Experimental Procedures and Operational Workflow:
Mass spectra were recorded in the first 5–10 minutes after bombardment began. Samples were prepared by dissolving the synthesized leuco form or oxidized Methylene Blue in the matrices, and FAB mass spectra were obtained under vacuum conditions.
5：Data Analysis Methods:
The mass spectra were analyzed by comparing peak intensities at m/z 284, 285, and 286, considering isotopic contributions and redox reaction products. The relative intensities were used to estimate the extent of reduction and oxidation processes.
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