Sub nanoampere ionization was investigated using glass emitters and paper spray substrates. An electrometer was set up to measure ionization current as low as 20 fA, while the ion trap mass spectrometer was operated to analyze ion current as low as 1 ion per second. Femto amp (100 s fA) ionization currents were generated using glass emitters with 90 nm tip or 4 μm tips. Using the 4 μm emitter tips, both the fA mode and the regular nanoESI mode were generated. Mass spectra produced by the fA mode ESI were >3 order of magnitude less intense than those produced by nanoESI mode. Beyond generating ESI type of ions, fA mode ESI generates native cytochrome c charge states without using any buffering agent. Femto amp ionization was also observed when conducting paper spray ionization, as well as when ionizing dry paper substrate without solvent. Ultra-low current ionization allowed direct analysis of undiluted sample matrices without carryover contamination. Samples collected and stored on a dried paper substrate were analyzed with no sample preparation.

使用玻璃发射器和喷纸基材研究了亚纳安电离。设置静电计以测量低至 20 fA 的电离电流，而操作离子阱质谱仪以分析低至每秒1 个离子的离子电流。毫微微安培 (100 s fA) 电离电流是使用具有 90 nm 尖端或 4 μm 尖端的玻璃发射器产生的。使用 4 μm 发射器尖端，生成了 fA 模式和常规 nanoESI 模式。fA 模式 ESI 产生的质谱比 nanoESI 模式产生的质谱强度低 3 个数量级以上。除了生成 ESI 类型的离子，fA 模式 ESI 生成天然细胞色素c不使用任何缓冲剂的电荷状态。在进行纸喷雾电离时，以及在没有溶剂的情况下电离干燥的纸基材时，也观察到了毫微微安培电离。超低电流电离允许直接分析未稀释的样品基质，而不会产生残留污染。在没有样品制备的情况下分析收集并储存在干燥纸基材上的样品。