Development of a miniaturized diffusive gradients in thin films (DGT) device

A miniaturized diffusive gradients in thin films (DGT) device with a sampling window which is 16 times smaller than the conventional DGT device was developed. Its main advantage is the reduced volume of solution necessary for deployment, which extends its potential applications. The design of the miniaturized DGT device was also improved compared with the conventional DGT device, such that the area of the diffusive gel layer that allows the diffusion of metal towards the binding gel layer has the same diameter as the opening in the cap of the device and no additional metal is accumulated due to lateral diffusion as is the case for the conventional device. A good correlation between the metal concentration directly measured and the concentration estimated with the help of the DGT equation was obtained using this device in synthetic solutions (10 μg L−1 Cd, 0.01 M NaNO3, pH 6). The capacity of the device for Cd was ∼20 μg, potentially allowing long term measurements to be performed. Metal accumulation increased linearly with deployment time up to 28 h and showed the theoretically expected dependence on diffusive layer thickness. The diffusive boundary layer thickness of ∼0.2 mm in stirred solution was considered for accurate quantification of concentration. There was no difference between concentrations of labile metal measured in natural waters using the new miniaturised devices and the conventional devices.