Development and application of the diffusive gradients in thin films technique for simultaneous measurement of methcathinone and ephedrine in surface river water.

In this study, a passive sampling technique, diffusive gradients in thin films (DGT) was developed to simultaneously measure two drugs, methcathinone (MC) and ephedrine (EPH) in surface water. Four types of binding gels and four types of filter membranes were tested for the optimal configuration. XAD18 agarose binding gel and agarose diffusive gel, together with polyethersulfone filter membrane were used for measuring MC and EPH in the DGT device. 5% NH3 in acetonitrile was used as the elution solvent, with the elution efficiency for MC and EPH higher than 71%. At 25°C, the diffusion coefficients of MC and EPH in the diffusive gel were 7.60×10(-6)cm(2)s(-1) and 6.62×10(-6)cm(2)s(-1), respectively. The DGT was effective in a wide range of pH (4-11) and ionic strength (NaCl: 0.001-0.5M). The DGT device was deployed in Beijing urban surface water for successive 7days to measure the time-weighted concentrations of MC and EPH. Results showed that EPH was detected in all samples, while MC was below its detection limit. DGT concentrations were comparable to the concentrations determined by SPE. This study demonstrated that the developed DGT method was effective to monitor the two drugs in surface water in situ.