Chemical and Analytical Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008/Bldg. 5510, 37831-6365, Oak Ridge, TN.
J Am Soc Mass Spectrom. 1996 Feb;7(2):157-62. doi: 10.1016/1044-0305(95)00627-3.
This article reports the first electrospray (ES) mass spectrometry observation of molecular dications that were formed in solution by sequential one-electron oxidation of the neutral molecules [viz., nickel(II) and cobalt(II) octaethylporphyrin] via the controlled-current electrolytic (CCE) process inherent to electrospray. Dication formation was found to require (1) the addition of electrolyte to the sample solution, which increased the magnitude of the ES current and, therefore, increased the extent of analyte electrolysis in the ES capillary, (2) a relatively low solution flow rate, which increased the electrolysis time (i.e., the time the analyte remained in the capillary), thereby providing more time for the analytes to diffuse to the metal-solution interface and react, and (3) the use of a platinum ES capillary, which, because it is difficult to oxidize, increased the proportion of the faradaic current that might be provided by electrolysis of solution species compared to that proportion available when the typical stainless steel capillary is used. These interpretations of the data are made on the basis of the known characteristics of the CCE process inherent to ES, supplementary data obtained from direct solution-phase observation of the metalloporphyrin redox products formed within the different metal ES capillaries by means of a novel ES ion source, and off-line cyclic voltammetry studies of the metalloporphyrins performed by using platinum and stainless steel working electrodes.
本文报道了首例通过电喷雾（ES）中固有的恒流电解（CCE）过程，依次对中性分子（即镍（II）和钴（II）八乙基卟啉）进行单电子氧化，在溶液中形成分子二价阳离子的电喷雾质谱观察结果。二价阳离子的形成需要（1）向样品溶液中添加电解质，这增加了 ES 电流的幅度，从而增加了 ES 毛细管中分析物的电解程度，（2）相对较低的溶液流速，这增加了电解时间（即分析物在毛细管中停留的时间），从而为分析物扩散到金属-溶液界面并反应提供了更多的时间，以及（3）使用铂 ES 毛细管，因为它难以氧化，与使用典型的不锈钢毛细管时相比，可能由溶液物种电解提供的法拉第电流的比例增加。这些数据的解释是基于 ES 中固有的 CCE 过程的已知特征、通过新型 ES 离子源在不同金属 ES 毛细管内直接观察到的金属卟啉氧化还原产物获得的补充数据，以及使用铂和不锈钢工作电极进行的金属卟啉离线循环伏安研究。
