Measurements of kinetic energy distributions of molecular ions ejected into an extraction field by matrix-assisted laser desorption are reported. The measurements were made in a time-of-flight mass spectrometer with an electrostatic mirror by measuring the reflected signal as a function of the difference between the accelerating voltage and the voltage applied to the mirror. The molecular ions were found to have less kinetic energy than the extraction field alone would normally provide, i.e., we observed an energy deficit. Under conditions typical for a matrix-assisted laser desorption experiment, the deficit is about 24 eV for molecular ions of insulin. The size of the deficit increases with the intensity of the molecular ion signal, and the molecular weight of the protein; it is also larger for negative molecular ions than for positive molecular ions.
Phthalate esters (PAEs) have attracted much attention because of their ubiquity and toxicity. However, previous studies mainly focused on the occurrence of PAEs controlled by the Environmental Protection Agency and neglected most uncontrolled PAEs. In this study, the occurrence of 21 PAEs, including 6 controlled and 15 uncontrolled PAEs, was investigated in polyethylene terephthalate (PET)-bottled drinking water samples purchased from markets in Beijing. Seventeen PAEs were detected in all samples, with dibutyl phthalate, diisobutyl phthalate, and dimethyl phthalate as the predominant compounds. Correlation analysis suggested that PET bottles might be one of the potential sources of PAEs in PET-bottled drinking water. The human health risks assessments indicated little or no risks from four controlled PAEs in bottled water. In comparison, the risks of uncontrolled PAEs should be of greater concern for their ubiquities in bottled drinking water.
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