Detecting Nitrosamines in Drinking Water Using GC–IMS

A study by researchers from Bonn-Rhein-Sieg University of Applied Sciences (Rheinbach, Germany) and the University of Duisburg-Essen (Essen, Germany) reported on the development, optimization, and pre-validation of a gas chromatography–ion mobility spectrometry (GC–IMS) method for the detection of nine N-nitrosamines (N–NOs) in drinking water (1). The method included a two-step enrichment strategy using solid-phase extraction (SPE) followed by in-tube extraction (ITEX). The study was published in the Journal of Chromatography Open.

N–nitrosamines are a class of organic compounds classified by the International Agency for Research on Cancer (IARC) as probable human carcinogens (2). Their detection in drinking water is critical due to their formation during disinfection processes and their presence in industrial and pharmaceutical waste. Regulatory limits for compounds like N-Nitrosodimethylamine (NDMA) are typically set in the low ng/L range in countries such as Germany, the US, the UK, and Canada.

Mass spectrometry (MS) is commonly used for trace-level analysis of N–NOs but can be resource- and cost-intensive. GC–IMS presents an alternative robust detection strategy that may be suitable for laboratories with limited access to high-end MS equipment.

The study combined SPE and ITEX as sequential preconcentration steps before GC–IMS analysis. SPE was used to isolate N–NOs from 1-L water samples, with elution in dichloromethane. The eluate was then dried, concentrated, and subjected to ITEX using a Tenax TA-packed syringe for analyte trapping and thermal desorption. Parameters for the ITEX process were optimized using a simplex self-directing design (SSD) algorithm, which adjusted extraction and desorption temperatures and agitation time. Optimization led to improved signal intensity for low-abundance nitrosamines, allowing the method’s calibration range to be reduced 10-fold, from 50 to 5 ng/L. Calibration was performed using seven concentration levels (5–50 ng/L), with external standards analyzed in triplicate. Signal intensities were based on the summed volumes of monomer and dimer ion species for each analyte, adjusted relative to a solvent-based surrogate peak. Regression analysis confirmed the suitability of a linear calibration model for all nine nitrosamines, with R² values ≥0.94 for most compounds.

Recoveries from four different water matrices (ultra-pure, tap, branded drinking water, and fountain water) ranged from 27.3% to 114.5%, with most analytes exceeding the 70% threshold recommended in EPA Method 521 (3). Exceptions included NDMA, N-Nitrosomethylethylamine (NMEA), and N-Nitrosodi-iso-propylamine (ND-isoPA), which had lower recoveries, likely a result of volatility and matrix effects.

Detection limits calculated using both US EPA and German DIN methods varied by matrix and analyte. Using the DIN EN ISO 22065 approach (4), detection limits for most compounds were between 1.12 and 12.48 ng/L. These detection limits are within or near the required regulatory limits for drinking water in a number of countries.

By implementing two enrichment steps during sample preparation, GC–IMS demonstrated comparable performance to GC–MS/MS, offering sufficient sensitivity for monitoring nitrosamines in drinking water at regulatory-relevant levels. The solvent-free nature of ITEX and the reduced instrument complexity of IMS present operational benefits, though the authors acknowledged that manual steps in SPE and extract handling may introduce variability. The method offers lower instrumentation costs and operational simplicity, with performance metrics—particularly for detection limits and recoveries—falling within the acceptable range for many regulatory applications. Further optimization, including automation of the SPE step and compound-specific validation, could enhance reproducibility and broaden the method’s applicability.

References

(1) Hinz, J.; Wickneswaran, K.; Telgheder, U.; Wirtz, M. (2025). Development, Optimisation, and Pre-validation of a Gas Chromatography–Ion Mobility Spectrometry Method with Preliminary Twofold Enrichment for the Sensitive Detection of N-Nitrosamines in Drinking Water. J. Chrom. Open 2025, 7, 100220. DOI: 10.1016/j.jcoa.2025.100220

(2) Agents Classified by the IARC Monographs, Volumes 1–138. International Agency for Research on Cancer website. https://monographs.iarc.who.int/agents-classified-by-the-iarc/ (accessed 2025-05-13).

(3) Munch, J W. METHOD 521: DETERMINATION OF NITROSAMINES IN DRINKING WATER BY SOLID PHASE EXTRACTION AND CAPILLARY COLUMN GAS CHROMATOGRAPHY WITH LARGE VOLUME INJECTION AND CHEMICAL IONIZATION TANDEM MASS SPECTROMETRY (MS/MS). (U.S. Environmental Protection Agency, Washington, DC, 2005).

(4) German Institute for Standardization, DIN ISO 22065:2020 workplace air - gases and vapours - requirements for evaluation of measuring procedures using pumped samplers (2021).