Determination of the cardiac drug amiodarone and its N-desethyl metabolite in sludge samples

• Simultaneous determination of amiodarone and N-desethylamiodarone in sludge.
• Effective extraction with reduced matrix effects during LC–ESI(+)–MS determination.
• Accumulation of the active drug and the N-desethyl species in sludge.
• Persistence in lime stabilized sludge.
• Identification of mono-iodinated forms of amiodarone and N-desethylamiodarone.

For the first time, a procedure for the simultaneous determination of the iodinated drug amiodarone and its major metabolite, N-desethylamiodarone, in sludge from urban sewage treatment plants (STPs) is proposed. Matrix solid-phase dispersion (MSPD) followed by on-line cationic exchange clean-up, in modular configuration, was used as sample preparation technique. Liquid chromatography with tandem mass spectrometry (LC–MS/MS), based on a hybrid quadrupole time-of-flight (QTOF) system, was employed for the selective determination of target compounds. The optimized procedure provided exhaustive recoveries with little effect of the sample matrix in the efficiency of electrospray ionization (ESI). The overall recoveries of the method ranged between 95 and 111%, for samples spiked at different concentration levels. The achieved limits of quantification (LOQs) remained below 10 ng g−1 for both compounds, and the linear response range extended up to 2500 ng g−1. Amiodarone and N-desethylamiodarone were ubiquitous in sludge samples, from different STPs located in the Northwest of Spain, with maximum concentrations above 300 ng g−1 referred to the freeze-dried matrix. They were also present in stabilized sludge (mixed with lime and thermally dehydrated), which is mostly disposed in agriculture fields as fertilizer. Furthermore, mono-iodinated analogues of amiodarone and N-desethylamiodarone were also tentatively identified in some samples from their accurate MS and MS/MS spectra.