C & N Isotope Analysis of Diclofenac to Distinguish Oxidative and Reductive Transformation and to Track Commercial Products

Abstract

Although diclofenac is frequently found in aquatic systems, its degradability in the environment remains imperfectly understood. On the one hand, evidence from concentration analysis alone is inconclusive if an unknown hydrology impedes a distinction between degradation and dilution. On the other hand, not all transformation products may be detectable. As a new approach, we therefore developed GC-IRMS (gas chromatography-isotope-ratio mass-spectrometry) analysis for carbon and nitrogen isotope measurements of diclofenac. The method uses a derivatization step that can be conducted either online or offline, for optimized throughput or sensitivity, respectively. In combination with on-column injection, the latter method enables determination of diclofenac isotope ratios down to the sub-μgL(-1) range in environmental samples. Degradation in an aerobic sediment-water system showed strong nitrogen isotope fractionation (εN = -7.1‰), whereas reductive diclofenac dechlorination was associated with significant carbon isotope fractionation (εC = -2.0‰). Hence dual element isotope analysis bears potential not only to detect diclofenac degradation, but even to distinguish both transformation pathways in the environment. In an explorative survey, analysis of commercial diclofenac products showed significant differences in carbon and nitrogen isotope ratios, demonstrating a further potential to track, and potentially even to authenticate, commercial production batches.

13C- and 15N-Isotope Analysis of Desphenylchloridazon by Liquid Chromatography–Isotope-Ratio Mass Spectrometry and Derivatization Gas Chromatography–Isotope-Ratio Mass Spectrometry

“…Like most polar organic compounds, however, DPC is not amenable to GC as it decomposes before reaching a boiling point (see Table S1). To analyze the isotopic composition of such polar organic compounds, derivatization-GC-IRMS has been brought forward as alternative strategy 24,25,31,32 . This approach is chosen as the methylation of DPC enhances its GC suitability.…”

Multi-element isotope fractionation concepts to characterize the biodegradation of hydrocarbons — from enzymes to the environment

“…ME-CSIA for hydrocarbons relies on lambda (L) values expressing the slope of changing hydrogen and carbon isotope signatures in the course of hydrocarbon transformation reactions (d 2 H/d 13 C; see Figure 1). The combined analysis of other isotopes, for example, d 15 N/d 13 C [10] or d 13 C/d 37 Cl [11] has been recently also applied to characterize reactions upon substituted organics or micropollutants [12]; hence, ME-CSIA has become the state-of-the-art approach to identify distinct environmental transformation reactions but its relevance has to be thoroughly investigated.…”

Rapid analysis of diclofenac in freshwater and wastewater by a monoclonal antibody-based highly sensitive ELISA

“…It can be obtained as prescribed and as over-thecounter (OTC) with short dosing intervals. In Germany, for example, the yearly consumption exceeds 80 tons [8]. Depending on the efficiency of the WWTP, the parent drug and metabolites enter the environment, followed by bioaccumulation and impairment of aquatic wildlife like mussels and fish, possibly [9][10][11][12][13][14][15].…”