Abstract
In this short technical paper we demonstrate how aging of the micro-channel plate (MCP) detector in a PTR-ToF-MS instrument induces strong mass discrimination and detection non-linearity effects. Based on exemplary data from an 11-week measurement campaign we show how detector aging led to an m/z-dependent loss in detection efficiency in the m/z 33 (−19%) to m/z 205 range (−67%). Ion signals in the upper m/z range did not increase linearly with analyte concentration (0–150ppbv) when the MCP detector was not operated in the saturation regime. Both effects may lead to large errors in VOC quantification by PTR-ToF-MS if the instrument is not externally calibrated on a frequent basis. We also demonstrate that the current practice of minimizing ion feedback in the MCP detector will trigger the described problems. Our study may serve as a guide for diagnosing and optimizing PTR-ToF-MS detector performance.
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