Photo-ionization detector (pid) with multiple measuring cells and process using such a pid

A process for detecting an ionizable substance in a gas, the process comprising:

• providing a photo-ionization detector comprising:
• a radiation source;
• a measuring cell carrier;
• and a plurality of measuring cells mounted on the measuring cell carrier, each of the measuring cells comprising a measuring electrode having a measurable electrical property and each of the measuring cells being associated with a respective state of the photo-ionization detector;
• operating the photo-ionization detector sequentially in at least two different associated states, with operation of the photo-ionization detector in the state associated with one measuring cell of the plurality of measuring cells comprising the steps of:
• establishing a fluid connection between an environment of the photo-ionization detector and the associated measuring cell of the plurality of measuring cells such that the gas reaches the associated measuring cell of the plurality of measuring cells;
• emitting ionizing electromagnetic radiation from the radiation source towards the measuring cell carrier such that at least a part of the emitted electromagnetic radiation reaches the associated measuring cell of the plurality of measuring cells;
• with an ionization of ionizable substance in the gas changing the measurable electrical property of the associated measuring cell of the plurality of measuring cells, generating with the associated measuring cell of the plurality of measuring cells a signal depending on the electrical property, which signal correlates with a presence of ionizable substance in the gas;
• and
• separating at least one another measuring cell of the measuring cells from the environment.