Paper spray chemical ionization (PSCI) combined with mass spectrometry has been proposed as a sensitive method for the analysis of nonpolar aromatic compounds; however, the mechanism behind PSCI is not well understood. In the present study, the evidence for the occurrence of corona discharge is provided and its mechanism is proposed. Photographs taken with a highly sensitive camera evidently demonstrate the occurrence of corona discharge at the end of the triangular shape tip when a nonpolar solvent such as hexane was used at an applied potential of 6–7 kV. Nevertheless, corona discharge was not observed in the presence of a polar solvent. The occurrence of the corona discharge was attributed to charge accumulation in the dielectric layer generated by the nonpolar solvent on the fibers of the paper tip. Specifically, corona discharge was generated at the tip end when the charge approached a critical threshold. In the presence of a polar solvent, however, the dielectric layer was not generated and, hence, corona discharge was not observed. Based on this information, three nonpolar solvents were selected and their sensitivity for analyzing the phenanthrene and maltene fractions of crude oil was evaluated. Chlorobenzene provided the highest signal abundance; therefore, it was suggested as the optimum solvent for PSCI. Notably, the fundamental understanding of corona discharge in PSCI acquired in this study provides a basis for further improvement of this technique by way of surface modification.

中文翻译：

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纸张喷雾化学电离现象背后的机理及溶剂的选择

纸喷雾化学电离（PSCI）与质谱相结合已被提议作为一种分析非极性芳族化合物的灵敏方法。但是，PSCI背后的机制尚不清楚。在本研究中，提供了发生电晕放电的证据并提出了其机理。用高灵敏度照相机拍摄的照片显然表明，当在6-7 kV的施加电势下使用非极性溶剂（如己烷）时，在三角形尖端的末端会发生电晕放电。然而，在极性溶剂的存在下未观察到电晕放电。电晕放电的发生归因于由非极性溶剂在纸头的纤维上产生的电介质层中的电荷积累。具体来说，当电荷接近临界阈值时，在尖端产生电晕放电。然而，在极性溶剂的存在下，没有产生介电层，因此，未观察到电晕放电。基于此信息，选择了三种非极性溶剂，并评估了它们对分析原油中菲和麦芽馏分的敏感性。氯苯提供了最高的信号丰度。因此，建议将其作为PSCI的最佳溶剂。值得注意的是，本研究中获得的PSCI中对电晕放电的基本理解为通过表面改性进一步改进该技术提供了基础。没有观察到电晕放电。基于此信息，选择了三种非极性溶剂，并评估了它们对分析原油中菲和麦芽馏分的敏感性。氯苯提供了最高的信号丰度。因此，建议将其作为PSCI的最佳溶剂。值得注意的是，本研究中获得的PSCI中对电晕放电的基本理解为通过表面改性的方式进一步改进该技术提供了基础。没有观察到电晕放电。基于此信息，选择了三种非极性溶剂，并评估了它们对分析原油中菲和麦芽馏分的敏感性。氯苯提供了最高的信号丰度。因此，建议将其作为PSCI的最佳溶剂。值得注意的是，本研究中获得的PSCI中对电晕放电的基本理解为通过表面改性进一步改进该技术提供了基础。