According to a recent study published on Analytical Chemistry, a novel electrostatic field ion funnel focusing technology called direct current (DC)-ion funnel, was proposed by researchers from the Hefei Institutes of Physical Science (HFIPS) of the Chinese Academy of Sciences (CAS). It realizes ion focusing with only a DC electric field, thus improving the sensitivity of mass spectrometers.

Proton transfer reaction mass spectrometry (PTR-MS) is a valuable tool in many fields. However, how to ensure the high sensitivity while reducing volume and power remains a difficult problem for miniaturized mobile PTR-MS (M-PTR-MS). To improve the sensitivity of PTR-MS instruments, researchers generally use a radio frequency (rf)-focusing electric field in drift tubes to focus ions, which increases power consumption and volume and is therefore not suitable for M-PTR-MS.  

In this study, the researchers replaced the traditional ring electrode with five curved electrodes and a metal mesh welded to the curved electrode. The diminishing inner diameter of the five curved electrodes they designed helps the efficient ion focusing. That’s how they realized the DC-ion funnel focusing in DC electrical field.

The new structure has many advantages. Compared with traditional drift tube, the sensitivity of the DC-ion funnel tube was increased from 3.8 times to 7.3 times. In addition, the new DC ion funnel drift tube retains the soft ionization in PTR-MS.  

The researchers applied this DC-ion funnel technology to the M-PTR-MS for mobile monitoring of atmospheric volatile organic compounds. And the result was impressive.

In addition, the DC-ion funnel can easily be coupled to other types of mass spectrometers to improve their detection sensitivity, which can provide key technical support for the development of frontier mass spectrometers.  

This work was supported by the National Natural Science Foundation of China, the Youth Innovation Promotion Association of CAS, the Anhui Provincial Key R&D Program, and the HFIPS Director's Fund, etc.

Focusing effect of the DC-ion funnel. (Image by ZHANG Qiangling) 

Cover art of the paper. (Image by ZHANG Qiangling)