In AB SCIEX systems, we have developed the QJet® ion guide, a form of RF quadrupole that focuses the ions while allowing the gas to be pumped away. For the AB SCIEX QTRAP® 6500 System, our new and highest-performance instrument, we have developed a two-section QJet that captures the ion beam from the first orifice and focuses it through the following aperture with an efficiency of approximately 50%, an impressive figure of merit under the circumstances.
As indicated by the growth curve in Figure 1, the current level of sensitivity achieved by the QTRAP 6500 System represents a significant improvement over the earlier generation AB SCIEX QTRAP 5500 system. This improvement is due to the increased efficiency provided by the heating and desolvation in the IonDrive™ Turbo V ion source combined with the larger orifice and two-section IonDrive™ QJet described above.
An important development in this product has also been to increase the dynamic range of the pulse-counting detection system so that count rates of greater than 50 million ions per second can be measured without saturation. This is a major improvement over the more conventional pulse-counting detection systems that were limited to an upper count rate of only about 5 million ions per second.
The combination of a high-dynamic range continuous-dynode multiplier and a new amplifier that provides low noise and allows operation of the multiplier at a relatively low gain has resulted in a dynamic range of greater than six orders of magnitude, which now better matches the dynamic rage of the ion source.
As the analytical needs of the bioanalysis community continue to increase, more and better approaches to generating, sampling, and detecting ions by mass spectrometry will be required. However, the growth curve of sensitivity will become more and more difficult to maintain as we approach the limit of measuring and detecting nearly every ion injected.
The most significant challenges ahead are in developing mass spectrometry techniques that are more selective (to reduce noise from isobaric interferences), faster, and more cost efficient. The need for creative physicists, chemists, and engineers to answer this challenge in instrument design will continue.