Lübbert Christian, Peukert Wolfgang
FAU Erlangen-Nuremberg, Institute of Particle Technology, Erlangen, Germany.
J Mass Spectrom. 2019 Apr;54(4):301-310. doi: 10.1002/jms.4315.
The presence of electrochemical reactions occurring in an electrospray processes at the point where the current enters the liquid is discussed since the early 1990's. This current transfer to the liquid results in oxidation or reduction of either electrolyte species in the liquid sprayed or of the electrode material in contact with the liquid. As a result, new chemical species are generated. These products of the electrochemical reaction might be detected as altered species in mass spectra; they might be volatile and not recognized at all or accumulate on the electrode surface and cause cross contamination later on. In other cases, it might happen that the products of the electrochemical reactions are the only detectable species formed from an otherwise nondetectable analyte. An electrospray setup in which electrochemical reactions do not interfere with the analyte under investigation excludes the electrochemical reaction as source of sample contamination and sample altering and may serve as reference setup for experiments focused on the electrochemical reaction itself. We present a simple and inexpensive current coupling approach and specify operation conditions for which any impact of the electrochemical reaction on the sample under investigation is inherently excluded. On the basis of a practical example, we show the impact of the electrochemical reaction on sample composition and demonstrate the benefit of using the proposed current coupling method. Because of the obvious benefit of this method and its simple realization, it has the potential to be employed as standard feeding approach, especially for electrosprays operated at small flow rates.
自20世纪90年代初以来，人们一直在讨论在电喷雾过程中电流进入液体的位置发生的电化学反应。这种电流向液体的转移会导致被喷雾液体中的电解质物种或与液体接触的电极材料发生氧化或还原。结果，会产生新的化学物种。这些电化学反应的产物可能在质谱中被检测为改变的物种；它们可能是挥发性的，根本无法识别，或者积聚在电极表面，随后导致交叉污染。在其他情况下，可能会出现电化学反应的产物是由原本无法检测到的分析物形成的唯一可检测物种的情况。一种电喷雾装置，其中电化学反应不会干扰所研究的分析物，排除了电化学反应作为样品污染和样品改变的来源，并且可以用作专注于电化学反应本身的实验的参考装置。我们提出了一种简单且廉价的电流耦合方法，并指定了操作条件，在这些条件下，电化学反应对所研究样品的任何影响都被固有地排除。基于一个实际例子，我们展示了电化学反应对样品组成的影响，并证明了使用所提出的电流耦合方法的好处。由于这种方法具有明显的优势且实现简单，它有可能被用作标准进样方法，特别是对于以小流速运行的电喷雾。
