One of the reasons that thermally induced reactions are not considered a crucial mechanism in ultraviolet matrix-assisted laser desorption ionization (UV-MALDI) is the low ion-to-neutral ratios. Large ion-to-neutral ratios (10(-4)) have been used to justify the unimportance of thermally induced reactions in UV-MALDI. Recent experimental measurements have shown that the upper limit of the total ion-to-neutral ratio is approximately 10(-7) at a high laser fluence and less than 10(-7) at a low laser fluence. Therefore, reexamining the possible contributions of thermally induced reactions in MALDI may be worthwhile. In this study, the concept of polar fluid was employed to explain the generation of primary ions in MALDI. A simple model, namely thermal proton transfer, was used to estimate the ion-to-neutral ratios in MALDI. We demonstrated that the theoretical calculations of ion-to-neutral ratios exhibit the same trend and similar orders of magnitude compared with those of experimental measurements. Although thermal proton transfer may not generate all of the ions observed in MALDI, the calculations demonstrated that thermally induced reactions play a crucial role in UV-MALDI.
The ion-to-neutral ratios of 25DHB matrix measured in this work are much smaller than some of the values reported in previous work using different methods and/or under different MALDI conditions.
An incorrect version of Figure 2(a) was shown in our recently published article. The correct figure and caption are given below. The authors regret this error. Figure 2. (a) represents the solvation energy. The Gibbs free energy, ΔG 1 , is illustrated by the above figure
A green method for
synthesizing Pd nanoparticles/graphene composites
from a choline chloride–oxalic acid deep eutectic solvent (DES)
without a reducing agent or a surfactant is reported. Deep eutectic
solvents are usually composed of halide salts and hydrogen-bond donors,
and many are biocompatible and biodegradable. The merits of deep eutectic
solvents include that they serve as reducing agents and dispersants,
and Pd nanoparticles are tightly anchored to graphene. The size and
dispersion of Pd particles are improved when supercritical carbon
dioxide (scCO
2
) is used because it has gaslike diffusivity
and near-zero surface tension, which results in excellent wettability
between the scCO
2
and the carbon surface. The prepared
sc-Pd NPs/GR/SPCE shows excellent activity toward glycerol oxidation
compared to composites not fabricated by scCO
2
processes.
This study demonstrates the potential of using this scCO
2
-assisted protocol combined with deep eutectic solvents to further
construct nanoparticles/graphene composites.
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