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A dual diffusive gradients in thin film (DGT) device method for in situ fractionation of dissolved inorganic Cr was developed by simultaneously deploying two types of DGT devices with different binding phases in tap water. The concentration of Cr(III) in the tap water determined by a DGT device with sodium poly(aspartic acid) (PASP) solution as the binding phase (PASP DGT) was 3.18 µg L−1, and the recoveries of the spiked Cr(III) were 97.9%–105.3%; the concentration of Cr(VI) in the tap water determined by a DGT device with poly(quaternary ammonium) salt (PQAS) solution as the binding phase (PQAS DGT) was 2.92 µg L−1, and the recoveries of the spiked Cr(VI) were 98.2%–107.7%. The ratios of the total Cr measured by DGT to the total Cr measured by ICP-MS were 102.9%–105.7%.

The technique of diffusive gradients in thin films (DGT) for the measurement of Ni2+ in waters was developed using sodium poly(aspartic acid) (PASP) solution as the liquid binding phase in the liquid-type DGT devices (PASP DGT). The Ni2+ uptake of PASP DGT increased linearly with time (r2 = 0.9990) with a DGT-labile fraction (Ψ) of 98.04 ± 1.76% in synthetic solution. The Ψ values of Ni2+ were measured in spiked river water (37.82 ± 2.79%) and spiked domestic wastewater (28.46 ± 1.87%). The stability constant (log K) of PASP–Ni was 8.56, indicating that PASP can coordinate strongly to Ni2+. The binding capacity of PASP DGT decreased with increase of ionic strength, whereas it remained fairly constant in the pH range 4–9. The results show that PASP can be used as a binding phase in the liquid-type DGT device for the measurement of Ni2+ in waters.