HOW TO MAINTAIN THE MCPS IN A SCIEX TRIPLETOF.

As the set of MCPs in a TripleToF nears the end of it’s life, the instrument optimisation will give a warning, usually at ~2400V. On average the MCPs in a 4600 and 5600 last 2 to 3 years but this is highly dependent on instrument usage. Simply, the number of counts that hit the MCPs, the lesser the lifetime. Therefore, running high concentration samples will have a significant impact on longevity.

The relationship between the ITC value and the detector is also simply explained. The ITC value represents the percentage of the ions going to the detector and there is a linear relationship between the ITC and amount of counts hitting the MCPs, e.g. when the ITC is set to 1, the output onscreen is 100 times the amount of counts hitting the MCPs.

This importance of these relationships is highlighted when comparing the life expectancy of the 6600, which has an ADC (Analog to Digital Converter) detector, compared to either the 4600 or 5600, which have TDCs (Time to Digital Converter) detectors. The upper limit on detection of a TDC, which controls the number of counts at any one time, is lower than an ADC. When using a 4600 or 5600, a TDC sync error will appear in the analyst sample queue when it has reached its upper limit on detection. By contrast, the ADC on the 6600 has such a high upper limit on detection, the number of counts does not present a significant issue when/in terms of…. Using an ADC detector (with higher ITC values) will, therefore, expose the MCPs to more ions resulting in a reduced MCP longevity. With a 6600 what you gain in terms of sensitivity, can be sacrificed in MCP replacement. The good news is that it is possible to maximise the signal with a good cleaning and servicing regime. However, there are different contamination issues to consider.
Due to TDC detector’s lower upper limit, more ions become trapped in a 4600 or 5600 by the ITC whereas in the 6600 ions are allowed to pass the ITC lens, into Q0 and onto the detector. Therefore, in a 4600 or 5600 most contamination issues will be due to a dirty ITC lens, but in a 6600 issues mainly arise with the ITC lens along with the Q0, IQ1 and Q1.

Trouble shooting
You will become aware of contamination issues if you get a false value in the detector during instrument optimisation. If your TripleToF is contaminated, ramping the detector can lead to higher MCP voltage (which in turn negatively impacts detector longevity). If your MCP voltage is rapidly increasing over time, you may need to clean the interface region of the TripleToF.
Contamination issues can mean that your sensitivity will be decreased especially at the lower masses, and a good indication that you have front-end issues is when you see a lot of rapid up and down spikes in the base-line and the top of peaks. We recommend that the first thing to try is a simple vent-and-clean. If the problem persists, your instrument may need a more thorough clean. Please don’t hesitate in contacting me if I can be of help.