Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Desorption Electro-Flow Focusing Ionization of Explosives and Narcotics for Ambient Pressure Mass



Thomas Forbes, Timothy M. Brewer, John Gillen


Desorption electro-flow focusing ionization (DEFFI), a desorption-based ambient ion source, was developed 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 high velocity fluid jet. An electric field is applied across this jet formation region, producing high velocity charged droplets that impinge on an analyte laden surface. The sample desorption and ionization processes operate similar to desorption electrospray ionization (DESI). The DEFFI characterization presented here 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. The DEFFI mass spectrometric response identified regimes of maximum analyte signal intensity and optimal signal-to-noise ratio as a function of applied potential. Transmitted current measurements and a scaling analysis were developed to identify the regimes of operation observed by the MS response. This analysis identified the functional relationship between DEFFI parameters and the optimal applied potential. In addition, the DEFFI response was directly compared to DESI-MS under similar operating conditions. This comparison established a wider 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, clearly demonstrating DEFFI's field compatibility.


Flow focusing, Ion source, Mass spectrometry, Desorption ionization


Forbes, T. , Brewer, T. and Gillen, J. (2013), Desorption Electro-Flow Focusing Ionization of Explosives and Narcotics for Ambient Pressure Mass, Analyst, [online], (Accessed June 22, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created August 5, 2013, Updated November 10, 2018