FY2010 - Oak Ridge National Laboratory

Seed Money Fund—
Chemical Sciences Division
Results and Accomplishments
A new type of detector for large ions was tested. A small amount of low-vapor-pressure ionic liquid was
applied to the surface of a metal conversion electrode to enhance the detector response for large ions, for
which commercial detectors do not work well. Several observations were made in these preliminary
experiments. The ionic liquid tested permitted a high vacuum of up to the 10 -7 torr range to be achieved, a
sufficient condition for operation of most mass spectrometers. However, the ionic liquid self-ionized
rapidly once the electrode applied electric field was larger than a certain threshold. To prevent such
ionization, a small metal mesh electrode was inserted at the opening where the large analyte ions enter the
detector. The voltage applied to this metal mesh electrode was typically 100 V. Sharp corners near the
liquid were all rounded to give a fairly uniform electric field. Most of the effort was spent in optimization
of the detector geometry design and testing. Ions were generated by electrospray ionization at ambient
conditions. The ions were introduced from an aerodynamic lens and guided through the quadrupole ion
guide. The detector was placed just below the guide exit lens. The distance to the electrode was also
optimized during this study to avoid self-ionization of the ionic liquid. This was necessary because the
applied voltage on the quadrupole rods was different for different molecule sizes. The detector response
was monitored during operation of the quadrupole ion guide, with a limiting orifice at the entrance of the
aerodynamic lens open and closed. On several occasions, our setup showed significant response to the
large ions. At optimized conditions, no background signals were detected. Once the analyte ions were
introduced into the aerodynamic lens, the detector responded. Overall, the heavy-ion detector worked for
large ion detection. However, a more clever design will be required to prevent self-ionization of the
liquid.
Our work with low energy ions (