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

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.

A qualitative analysis was applied for the determination of trace compounds at the parts per trillion in volume (ppt v ) level in the mass spectra of nitrogen of different qualities (5.0 and 6.0) under dry and humid conditions. This qualitative analysis enabled the classification and discovery of hundreds of new ions (e.g., [S x ]H + species) and artifacts such as parasitic ions and memory effects and their differentiation from real gas impurities. With this analysis, the humidity dependency of all kind of ions in the mass spectrum was determined. Apart from the inorganic artifacts previously discovered, many new organic ions were assigned as instrumental artifacts and new isobaric interferences could be elucidated. From 1140 peaks found in the mass range m/z 0-800, only 660 could be analyzed due to sufficient intensity, from which 463 corresponded to compounds. The number of peaks in nitrogen proton transfer reaction (PTR) spectra was similarly dominated by nonmetallic oxygenated organic compounds (23.5%) and hydrocarbons (24.1%) Regarding only gas impurities, hydrocarbons were the main compound class (50.2%). The highest contribution to the total ion signal for unfiltered nitrogen under dry and humid conditions was from nonmetallic oxygenated compounds. Under dry conditions, nitrogen-containing compounds exhibit the second highest contribution of 89% and 96% for nitrogen 5.0 and 6.0, respectively, whereas under humid conditions, hydrocarbons become the second dominant group with 69% and 86% for nitrogen 5.0 and 6.0, respectively. With the gathered information, a database can be built as a tool for the elucidation of instrumental and intrinsic gas matrix artifacts in PTR mass spectra and, especially in cases, where dilution with inert gases plays a significant role. K E Y W O R D Sgas impurities, gas traces, industrial gases, proton transfer reaction time-of-flight mass spectrometry, volatile organic compounds

The use of purified process gases as feedstock for subsequent processes requires a detailed verification of the gas purity to ensure long lifetimes of applied catalysts. Herein, the analytical infrastructure for the measurements of the cleaned gases is presented. An overview of all sampling points for the off‐ and on‐line analysis is given. The detailed decryption of the composition of the cleaned blast furnace gas, its main components as well as its traces are presented. Thereby, over 99 % of the overall signal strength of this complex gas matrix measured with a proton transfer reaction mass spectrometer with H3O+ as reagent ion could be revealed. Furthermore, by the example of the catalyst poison H2S, the necessity of monitoring continuously the gas matrix for certain compounds was proven.