Detector aging induced mass discrimination and non-linearity effects in PTR-ToF-MS

摘要

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 (0-150 ppbv) 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.