MCP microchannel plate detector

The detector is located at the end of the time-of-flight mass spectrometer and is responsible for converting incoming ions into electrical signals that can be recorded. An MCP (Microchannel Plate) is an electron multiplier comprising numerous extremely fine glass capillary channels: when ions strike the entrance of a channel, they excite secondary electrons, which are then multiplied in a cascading manner under the influence of the electric field within the channel, ultimately forming a readable pulse at the exit. The New Source ProC series utilises MCP detectors, which can achieve a gain of 10⁶ (one million times), amplifying the faint signal from a single ion to a level sufficient for accurate counting.

High gain offers two advantages. Firstly, sensitivity: even if only a very small number of ions arrive, they can still be detected; combined with a high-transmission-efficiency ion lens, this enables the instrument to respond to concentrations in the ppb range. Secondly, suppression of pulse interference: the MCP responds rapidly to short-pulse ion clusters and has a low background, enabling it to effectively shield against pulse interference signals and produce spectra with a high signal-to-noise ratio (S/N). This is particularly important for capturing transient radicals in online monitoring, or for distinguishing weak-signal molecules in imaging—weak and noisy signals are often not due to a lack of ionisation, but rather because the detector cannot ‘hear’ them clearly.

It is important to understand that detector gain, mass resolution and sensitivity are distinct factors. Gain determines ‘whether the signal is amplified to a measurable level’; resolution determines ‘whether peaks can be separated’; whilst sensitivity also depends on the efficiency of ionisation and transmission in the front-end. Only when these three factors work in concert can a mass spectrometer perform stable and accurate real-time analysis. To draw an analogy: resolution is like the focus of a camera lens (separating details), gain is like the amplification of an image sensor (making dark areas visible), and the ion lens is like the amount of light entering the lens (how much light is collected)—if any one of these elements is lacking, the final image will be distorted. Xin Ceyuan has optimised all three of these aspects simultaneously in its ProC series, enabling 10 ppb sensitivity, a resolution better than 3500, and a high signal-to-noise ratio to coexist within a single instrument.