Dual-Channel Off-Axis Ion Funnel With a Deflection Electrode

Rationale

In electrospray ionization mass spectrometry (ESI-MS) systems, two critical challenges persist: (1) under-expanded supersonic jets at the atmospheric pressure interface (API) cause ion losses and reduced transmission efficiency; (2) residual solvents and charged droplets entering vacuum stages lead to contamination and elevated chemical noise, degrading analysis accuracy.

Methods

A dual-channel off-axis ion funnel with a deflection electrode (DC-OFIDE) was developed to address these challenges. This device integrates three core components: an ion drift channel (IDC), an ion funnel channel (IFC), and a deflection electrode. The IDC and IFC are separated by conjoined gaps. Ions within the gas stream emanating from the API are extracted from the IDC via a deflection field, while a retarding axial field prolongs ions' residence time, ensuring efficient transfer to the IFC. This DC-OFIDE features an enlarged entrance aperture (Φ18 mm) to accommodate a multi-capillary interface, enhancing compatibility with high-conductance sample introduction systems.

Results

Compared with the original conventional ion funnel (CIF), the DC-OFIDE achieved a threefold enhancement in caffeine ion intensity and a broader m/z transmission window. It demonstrated robust neutral and droplet suppression, maintaining 80% ion intensity even under tripled serum volume infused. In drug screening of hair samples, baseline noises in drug ion peaks were reduced by 36%–82%, with a quadrupled signal-to-noise ratio improvement observed for 6-monoacetylmorphine.

Conclusions

This DC-OFIDE significantly enhances ion transmission efficiency and chemical noise suppression in ESI-MS, establishing its potential for high-fidelity analysis of complex samples.