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

• Sensitive and selective analysis method for nine N-nitrosamines in drinking waters. • Twofold enrichment via subsequent solid phase extraction and in-tube extraction. • Method development following US EPA guidelines. • Recoveries between 56.1 and 113.6 % for relevant N NOs in drinking water. • Method LODs and LOQs of 1.12 – 12.48 ng/L and 3.35 – 37.44 ng/L, respectively. N Nitrosamines have long been identified as a relevant contaminant in potable water due to their identification as probable human carcinogens. Thus, highly sensitive detection of these pollutants in the ultra-trace range is imperative to comply with strict regulatory specifications. To this end, many institutions rely on mass spectrometry-based analysis methods, which have the disadvantage of being cost- and resource intensive. This study aims to develop, optimise, and evaluate a gas chromatography-drift tube-ion mobility spectrometry (GC-IMS) based method with a twofold enrichment strategy consisting of solid phase extraction (SPE) followed by in-tube extraction (ITEX) of the eluate for nine different nitrosamines in drinking water in order to offer a sensitive alternative to the current state of the art. Optimisation of ITEX parameters was successfully performed using a simplex self-directing design approach, so that a calibration range between 5 and 50 ng/L could be achieved. The suitability of a linear regression model was demonstrated via analysis of variance (ANOVA) criteria. The analysis of different spiked drinking water samples allowed for the determination of the method’s accuracy (27.3 – 114.5 % across different nitrosamine analytes and matrices, with most above 70 % recovery) and detection limits (1.12 – 12.48 ng/L across different nitrosamine analytes and matrices), which fall within the range of required limit values. Tested drinking waters show innate nitrosamine concentrations well below detection limits and can thus be deemed free from contaminants.