River water samples were portioned into 50-100 mL samples. After immediate spiking of the IS mix, samples were then immediately processed on-site using the iMME sampler (figure ). The spiked river water samples were loaded into 50 mL syringes and pushed gently through GF/D (2.7 μm) and GF/F (0.7 μm) filters onto the conditioned Oasis HLB cartridge (conditioned using 1 mL of MeOH followed by 1 mL of H2O) at approximately 3 mL min -1 . After the river sample had been filtered, air was pumped through via the syringe several times to purge any remaining water. Cartridges were then transported at room temperature to the University of Bath, UK (from <1hrs in the UK to 2 days for samples collected in South Africa) for further processing.