National Institute of Standards and Technology, Materials Measurement Science Division, Gaithersburg, MD, USA.
Analyst. 2013 Oct 7;138(19):5665-73. doi: 10.1039/c3an01164j.
Desorption electro-flow focusing ionization (DEFFI), a desorption-based ambient ion source, was developed, characterized, and evaluated as a possible source for field deployable ambient pressure mass spectrometry (APMS). DEFFI, based on an electro-flow focusing system, provides a unique configuration for the generation of highly charged energetic droplets for sample analysis and ionization. A concentrically flowing carrier gas focuses the liquid emanating from a capillary through a small orifice, generating a steady fluid jet. An electric field is applied across this jet formation region, producing high velocity charged droplets that impinge on an analyte laden surface. This configuration separates the jet charging region from the external environment, eliminating detrimental effects from droplet space charge or target surface charging. The sample desorption and ionization processes operate similar to desorption electrospray ionization (DESI). DEFFI demonstrated strong signal intensities and improved signal-to-noise ratios in both positive and negative mode mass spectrometry for narcotics, i.e., cocaine, and explosives, i.e., cyclotrimethylenetrinitramine (RDX), respectively. A characterization of DEFFI ionization mechanisms identified operation regimes of both electrospray and corona discharge based analyte ionization, as well as limitations in overall signal. In addition, the DEFFI response was directly compared to DESI-MS under similar operating conditions. This comparison established a wider and more stable optimal operating range, while requiring an order of magnitude lower applied gas pressure and applied potential for DEFFI than DESI. These reductions are due to the physical mode of jet formation and geometric configuration differences between DEFFI and DESI, pointing to a potential benefit of DEFFI-MS for field implementation.
解吸电流动聚焦离子化（DEFFI）是一种基于解吸的环境离子源，已被开发、表征和评估为现场可部署环境压力质谱（APMS）的潜在源。DEFFI 基于电流动聚焦系统，为分析和离子化提供了一种独特的配置，用于产生高电荷高能液滴。同心流动载气通过小孔聚焦从毛细管中流出的液体，形成稳定的流体射流。在这个射流形成区域施加电场，产生高速带电液滴，这些液滴撞击载有分析物的表面。这种配置将射流充电区域与外部环境分开，消除了液滴空间电荷或目标表面充电对其的有害影响。样品解吸和离子化过程与解吸电喷雾离子化（DESI）类似。DEFFI 在正离子模式和负离子模式下的质谱分析中均表现出较强的信号强度和改善的信噪比，分别用于分析麻醉剂（可卡因）和爆炸物（环三亚甲基三硝胺（RDX））。DEFFI 离子化机制的表征确定了基于电喷雾和电晕放电的分析物离子化的操作模式，以及整体信号的限制。此外，在相似的操作条件下，将 DEFFI 的响应与 DESI-MS 直接进行了比较。这种比较建立了更宽和更稳定的最佳操作范围，同时与 DESI 相比，DEFFI 所需的施加气体压力和施加电势降低了一个数量级。这些降低归因于射流形成的物理模式和 DEFFI 与 DESI 之间的几何结构差异，表明 DEFFI-MS 可能具有现场实施的优势。
