15N-Isotope Analysis of Sulfamethoxazole by Derivatization-Gas Chromatography-Isotope Ratio Mass Spectrometry
P 5.4 in Methods, Models, Standards
Compound-specific isotope analysis is a powerful tool for characterizing degradation pathways through occurring isotopic effects. However, relying solely on isotopic information from a single element can present challenges in identifying transformation reactions in the field. Masking effects can lead to variations in isotope fractionation even if the same underlying degradation reaction prevails. In these cases, observed isotope enrichment factors may not accurately reflect the full isotope effects generated by the underlying reaction mechanism. Therefore, changes in isotope ratios of two elements relative to each other can allow for the distinction of different transformation pathways. The commonly employed technique for measuring polar and non-volatile compounds – LC-IRMS – is, however, restricted to carbon isotope measurements. To overcome this limitation and analyze nitrogen isotope values, we have spearheaded derivatization-GC-IRMS as an alternative. This work shows the development, optimization, and validation of a derivatization-GC-IRMS method for nitrogen isotope analysis of sulfamethoxazole, an antibiotic of environmental concern, as a basis for dual-element isotope analysis. Sulfamethoxazole was derivatized by methylation of the N1-position using TMSD. Different reaction times, temperatures, and TMSD equivalents showed yields of up to 87%, highlighting the potential for compound-specific isotope analysis.