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We present an effective procedure to differentiate instrumental artefacts, such as parasitic ions, memory effects, and real trace impurities contained in inert gases. Three different proton transfer reaction mass spectrometers were used in order to identify instrument-specific parasitic ions. The methodology reveals new nitrogen-and metalcontaining ions that up to date have not been reported. The parasitic ion signal was dominated by [N 2 ]H + and [NH 3 ]H + rather than by the common ions NO + and O 2 + . Under dry conditions in a proton transfer reaction quadrupole interface time-of-flight mass spectrometer (PTR-QiTOF), the ion abundances of [N 2 ]H + were elevated compared with the signals in the presence of humidity. In contrast, the [NH 3 ]H + ion did not show a clear humidity dependency. On the other hand, two PTR-TOF1000 instruments showed no significant contribution of the [N 2 ]H + ion, which supports the idea of [N 2 ]H + formation in the quadrupole interface of the PTR-QiTOF. Many new nitrogen-containing ions were identified, and three different reaction sequences showing a similar reaction mechanism were established. Additionally, several metal-containing ions, their oxides, and hydroxides were formed in the three PTR instruments. However, their relative ion abundancies were below 0.03% in all cases. Within the series of metal-containing ions, the highest contribution under dry conditions was assigned to the [Fe(OH) 2 ]H + ion. Only in one PTR-TOF1000 the Fe + ion appeared as dominant species compared with the [Fe(OH) 2 ]H + ion. The present analysis and the resulting database can be used as a tool for the elucidation of artefacts in mass spectra and, especially in cases, where dilution with inert gases play a significant role, preventing misinterpretations. KEYWORDS artefacts, industrial gases, parasitic ions, proton transfer reaction time-of-flight mass spectrometry, volatile organic compounds 1 | INTRODUCTION In the last decades, chemical ionization mass spectrometry (CIMS) 1,2 was established as a new and powerful tool for the on-line monitoring of trace amounts of volatile organic compounds (VOCs) without requiring additional pre-separation techniques such as gas chromatography. One of the important improvements of CIMS was the use of the hydronium (H 3 O + ) cation as primary ionization ion, which has led

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The utilization of industrial off‐gases as raw material requires a detailed knowledge on their time‐depending composition, especially with regard to trace components. Within the framework of the HüGaProp project (Hüttengas Properties) a measuring container and the analytical methods for the characterization of trace components in the three raw metallurgical gases was developed. The mobile container is deployed in the project Carbon2Chem® to characterize the available off‐gases at a steel mill and provide fundamental data to determine the required gas cleaning as well as the background for the further process design.

Selected ion flow tube mass spectrometry (SIFT‐MS) and proton transfer reaction mass spectrometry with switchable reagent ion capability (PTR+SRI‐MS) are analytical techniques for real‐time qualification and quantification of compounds in gas samples with trace level concentrations. In the detection process, neutral compounds—mainly volatile organic compounds—are ionized via chemical ionization with ionic reagents or primary ions. The most common reagent ions are H3O+, NO+ and O2+•. While ionization with H3O+ occurs by means of proton transfer, the ionization via NO+ and O2+• offers a larger variety on ionization pathways, as charge transfer, hydride abstraction and so on are possible. The distribution of the reactant into various reaction channels depends not only on the usage of either NO+ or O2+•, but also on the class of analyte compounds. Furthermore, the choice of the reaction conditions as well as the choice of either SIFT‐MS or PTR+SRI‐MS might have a large impact on the resulting products. Therefore, an overview of both NO+ and O2+• as reagent ions is given, showing differences between SIFT‐MS and PTR+SRI‐MS as used analytical methods revealing the potential how the knowledge obtained with H3O+ for different classes of compounds can be extended with the usage of NO+ and O2+•.