iFunnel Technology for enhanced sensitivity in triple quadrupole LC/MS

By Paul Momoh, Anabel Fandino, Ed Aisawa, Tim Schlabach, Ken Miller, and George Stafford
Agilent Scientists and Engineers

Triple quadrupole mass spectrometers are quantitation workhorses in many labs, where a number of applications demand the lowest possible limits of detection. Whether you analyze trace pesticides in food, low-level metabolites in serum, or biomarkers in plasma, better sensitivity means robust analyses and the ability to detect critical compounds at trace levels. With Agilent’s revolutionary iFunnel Technology on the Agilent 6490 Triple Quadrupole LC/MS System, you can benefit from up to 10-fold better sensitivity than previous systems.

Figure 1. The new Agilent 6490 Triple Quadrupole LC/MS with iFunnel Technology, shown here with the Agilent 1290 Infinity LC System, enables analyses at the zeptomole level.

Reducing the ion bottleneck in tandem LC/MS

Electrospray ionization (ESI) is robust and widely applicable for the analysis of many types of chemical compounds, but only one in 10³ to 10⁵ ions passes through the system and triggers a signal response at the MS detector.[1] This bottleneck fundamentally limits the sensitivity of LC/MS systems.

Agilent’s new iFunnel Technology combines the high ion generation and focusing of Agilent Jet Stream (AJS) thermal gradient focusing technology with a hexabore capillary sampling array. This setup enables a much larger fraction of the ESI spray plume to enter the mass spectrometer ion optics. A unique dual-stage ion funnel allows increased ion transmission, while evacuating a much higher gas load. The iFunnel Technology enables a new era in high-sensitivity analysis with zeptomole (10^-21 mole) detection limits achieved for the first time in a quadrupole-based tandem mass spectrometer at conventional flow rates.

New hexabore sampling capillary delivers more analyte ions

Prior to development of the iFunnel Technology, studies demonstrated that many ions formed in the collimated ESI plume were not captured by the mass spectrometer. Experiments that varied the lateral position of the AJS plume in front of the entrance capillary for the mass spectrometer revealed that the area of maximum ion generation occurs across a 3 to 5 mm horizontal region at the center of the plume. This means that even in the highly sensitive Agilent 6460 Triple Quadrupole LC/MS System (the previous generation instrument), many ions fail to enter the single-bore capillary.

Researchers have shown that multiple capillaries increase ion sampling efficiency and maintain good desolvation performance. A circular arrangement of six capillaries was chosen for the 6490 Triple Quadrupole system. However, increasing the number of capillaries increases the gas load on the mass spectrometer. The single-bore capillary on the Agilent 6460 Triple Quadrupole conducts about 1.5 L/min of atmospheric gas, while the hexabore capillary sampling array conducts about 9 L/min. The array samples many more ions from the collimated ESI plume, but requires their separation from a much larger volume of gas.

Figure 2. iFunnel dual ion funnel assembly removes atmospheric gas and neutral species, and focuses and directs ions into the low-pressure optics of the Agilent 6490 Triple Quadrupole. (Enlarge image.)

Figure 3. This sensitivity comparison for alprazolam, 1 pg on-column, shows that the 6490 Triple Quadrupole LC/MS with iFunnel Technology has 10-fold better sensitivity than the 6460 Triple Quadrupole system. (Enlarge image.)

Figure 4. 100 attograms of verapamil, on-column, demonstrates the excellent sensitivity of the new 6490 Triple Quadrupole LC/MS. (Enlarge image.)

Innovative dual ion funnel focuses ions while reducing pressure

The solution to this challenge is the addition of an ion funnel system – an ion optics element that efficiently captures and confines highly dispersed ions, and directs the flow of ions through the initial stages of the MS system, which are under higher gas loads.

A dual ion funnel assembly was chosen. It removes gas in two stages, as shown in Figure 2. The initial funnel operates at high pressure and is pumped by a dedicated rough vacuum system. The funnel voltages and radio frequency (RF) fields propel ions forward, and focus the ion trajectories to align with the entrance to the second, low-pressure funnel. The process is repeated with the second ion funnel.

Dramatic sensitivity gains

Relative to the 6460 Triple Quadrupole system, the new 6490 Triple Quadrupole LC/MS with iFunnel Technology shows a ten-fold gain in signal-to-noise ratio for alprazolam, with both systems using Agilent Jet Stream technology (Figure 3). Significant gains in sensitivity for many compounds in both positive ion and negative ion modes have been observed with the new 6490 LC/MS.

Dramatic gains in signal intensity achieved with iFunnel Technology translate into significantly improved limits of detection. Injection of just 100 attograms of verapamil on-column produces a response that is clearly distinguishable from noise (Figure 4). The limit of detection in this case is approximately 100 zeptomoles of verapamil.

In summary, Agilent’s iFunnel Technology combines unique Agilent Jet Stream technology with a hexabore capillary sampling array and a dual-stage ion funnel assembly to increase ion sampling and transmission from the AJS spray plume into the 6490 ion focusing optics. This new technology produces:

Significant, stable gains in tandem LC/MS sensitivity
Dramatic improvements in both positive ion and negative ion sensitivity
Zeptomole detection limits for some compounds

If you need more sensitivity for your triple quadrupole analyses, learn all the details by reading the full technical overview about iFunnel Technology (5990-5891EN). Then contact your Agilent Representative for additional information.

Reference

J. S. Page, R. T. Kelly, K. Tang, and R. D. Smith, “Ionization and transmission efficiency in an electrospray ionization-mass spectrometry interface,” J. Am. Soc. Mass Spectrom., 18:1582-1590, 2007.

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