Cover story of the Journal of the American Society for Mass Spectrometry reports findings of Stevens Scientists on a novel ionization technique for mass spectrometry

Desorption Ionization by Charge Exchange (DICE) for determination of compounds such as cholesterol


Hoboken, NJ – “If only elephants could fly!” At least that was a lament of scientists analyzing biological macromolecules by mass spectrometry before the year 1984.

At that period of time, it was difficult to produce gaseous ions from nonvolatile big molecules.  Recently, Chang-Ching Chan, a Ph.D. student of Professor Athula Attygalle of Stevens Institute of Technology, Chemistry Department, along with two other collaborators, has made a significant advance in the process of producing gas phase molecular ions from difficult molecules such as cholesterol. Together, the group has developed a new desorption ionization technique called Desorption Ionization by Charge Exchange (DICE), that has been used to analyze compounds that do not necessarily ionize well by traditional Desorption Electrospray Ionization (DESI). 

Professor J.B. Fenn of Virginia Commonwealth University (Richmond, Virginia) was the first to revolutionize the world of mass spectrometry in 1984 by inventing the Nobel prize-winning technology Electrospray Ionization (ESI) which he called in his Nobel lecture: “Electrospray Wings for Molecular Elephants.”  This ESI technique is very efficient in generating ions from biological macromolecules.  However, many sample preparation steps have to be taken before the “electrospray wings” can be finally attached to those “molecular elephants” by the ESI technique.

Professor Cooks of Purdue University (West Lafayette, Indiana) made the next major technological breakthrough in mass spectrometry with the introduction of DESI in 2004. The DESI technique is an ESI-related method that eliminates prior sample preparation and can ionize compounds directly in their native form. Because of its ease of use, sensitivity and a wide dynamic range for quantification, the DESI technique has found many applications ranging from homeland security, forensic science, pharmaceutical, environmental and biological analyses. A limitation of the DESI technique, however is that it does not generate bursts of gaseous ions from some important compounds, particularly, from relatively less polar compounds such as cholesterol.

The ionization mechanism of DICE and DESI are different: DICE ionizes analytes primarily by removing an electron from the neutral entity whilst DESI mainly removes or adds a proton, or adds an anion or a metal cation, to the compound of interest. Because of this difference in the ionization mechanism, under positive-ion generation mode, DICE ionizes some compounds such as cholesterol (steroid molecule), 1, 4-hydroquinnone (ecotoxic), limonene (flavor) and thymol (antiseptic) better than DESI.  In addition, DICE has shown to generate little, if any, metal cation adducts which some scientists consider as undesired complications. For example, DICE can ionize cholesterol (deliberately spiked) from a salty biological matrix such as human urine without detecting any of the common salt such as sodium or potassium.

Although the DICE technique has advantages over the DESI method for certain compounds, the DICE technique is not universal; DICE works better for some compounds while DESI works better for others. Another important feature about DICE is that it can be easily combined with DESI to broaden the range of compounds that can be analyzed by mass spectrometry within a single experiment.

The significance of the DICE technique has been recognized by the scientific community by selecting it to be featured on the cover page of the September issue of Journal of the American Society of Mass Spectrometry.  Stevens filed a provisional patent in October 2009 for the ownership of DICE technique.
For more information, please contact Dr. Attygalle at

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