A derivatization gas chromatography isotope ratio mass spectrometry (derivatization-GC-IRMS) method is developed to access nitrogen isotope values during degradation processes for further mechanistic insights.

The continuous introduction of micropollutants into the environment through livestock farming, agricultural practices, and wastewater treatment is a major concern. Among these pollutants are synthetic sulfonamide antibiotics such as sulfamethoxazole, which are not always fully degraded and pose a risk of fostering antimicrobial resistance. It is challenging to assess the origin and degradation of sulfonamides with conventional concentration measurements. Compound-specific stable isotope ratios (¹³C/¹²C or ¹⁵N/¹⁴N) can provide additional information because they can trace different sources of the same chemical by their different isotopic fingerprints and detect transformation in the environment based on the detection of associated isotope effects. This study introduces compound-specific isotope analysis of nitrogen-isotope ratios at natural abundances by derivatization-gas chromatography hyphenated with isotope ratio mass spectrometry (derivatization-GC-IRMS) as a new and more precise method for tracing the origin and degradation of sulfonamides. Here, sulfamethoxazole was used as a model compound to develop and optimize the derivatization conditions using (trimethylsilyl)diazomethane as a derivatization reagent. With the optimized conditions, accurate and reproducible δ¹⁵N analysis of sulfamethoxazole by derivatization-GC-IRMS was achieved in two different laboratories with a limit for precise isotope analysis of 3 nmol N on column, corresponding to 0.253 µg non-derivatized SMX. Application of the method to four further sulfonamides, sulfadiazine, sulfadimethoxine, sulfadimidine, and sulfathiazole, shows the versatility of the developed method. Its benefit was demonstrated in a first application, highlighting the possibility of distinguishing sulfamethoxazole from different suppliers.  

Publication:

Dou, Q.; Canavan, A.; Fu, Y.; Xiang, L.; Wang, Y.; Wang, X.; Jiang, X.; Dirr, C.; Wang, F.; Elsner, M., Nitrogen stable isotope analysis of sulfonamides by derivatization-gas chromatography-isotope ratio mass spectrometry. Analytical and Bioanalytical Chemistry 2024, 416(19), 4237-4247.