In contrast to previous methods [2], [14], [15], [16] and [17], sample clean-up was mainly performed in one step by solid-phase extraction replacing the liquid–liquid extraction protocol. Overall, this resulted in a significant reduction of analysis time and solvent consumption. In addition, SPE is less error-prone and is ideally suited for automatisation. A polystyrene–divinylbenzene copolymer was used as sorbent material which enables a strong and quite selective retention of the nitro-aromatic derivatives (π–π-interaction) while most of the matrix compounds are more weakly retained. Quantitative desorption of the analytes from the SPE column was achieved with 3 ml of ethyl acetate as eluent.