Chemical Ionization Mass Spectrometry (CIMS) is one of the most powerful tools for real-time monitoring of volatile and semi-volatile organic compounds. Until now, however, positive reagent ions to detect moderately oxygenated and basic molecules under ambient-pressure conditions where either toxic, corrosive or elastomer-degrading. Our new work solves that problem with uronium—a reagent cation generated byX-ray desorption of solid urea.
Unlike reagent gases that demand careful handling or frequent replacement, urea is a benign, non-volatile solid. Exposed to a controlled X-ray source in our MION2 inlet, it continuously produces uronium ions for months-long operation—no daily tuning, no consumable refills, and no toxic or corrosive byproducts.These ions form exceptionally strong, humidity-resistant clusters with target analytes, achieving detection limits in the pptv–ppqv range without sacrificing stability.
Operating entirely at atmospheric pressure, uronium CIMS eliminates complex vacuum interfaces and accelerates sampling response times. In practice, it fills a critical gap in positive-mode ionization: making the direct analysis of amines, moderately oxygenated, and other traditionally “tricky” compounds far more straightforward, even in the presence of water vapor or mixed pollutant streams.
Here’s how it works in three steps:
Our recent calibration experiments demonstrated a linear, humidity-robust response to a wide panel of amines, ethers, and semivolatiles. In atmospheric oxidation studies of α-pinene and dimethyl sulfide, uronium CIMS captured a wide spectrum of reaction products, complementing both low-pressure positive and negative-mode techniques. In a field comparison with a QC-TILDAS laser spectrometer, uronium CIMS achieved 10s ppt-level accuracy and good agreement with the standard method for ambient ammonia measurements
We’ve published these findings as a preprint to share this breakthrough ASAP, and we invite the community’s feedback. Whether you’re in atmospheric science, environmental monitoring, or process control, your insights and questions will help refine and expand uronium CIMS applications.
🔗 Read the full preprint on ChemRxiv
💬 Join the conversation: Share your thoughts or suggestions on social media or the pre-print site.
Thank you to everyone at Karsa, the University of Helsinki, Tampere University, and our instrumentation partners for making this work possible. We can’t waitto see how Uronium CIMS will drive the next generation of trace-gas analysis!
We’re proud to share that Uronium CIMS is currently patent-pending.
