A calibration approach for a passive sampler based on a polymer inclusion membrane (PIM) for in situ Zn monitoring in Catalan rivers

Abstract

Time-weighted average (TWA) concentrations of Zn(II) were monitored in a mine-contaminated river in Catalonia (the Osor) by an in situ sampling point-specific kinetic calibration using a polymer inclusion membrane (PIM)-passive sampler. The PIM was composed of a polymer, cellulose triacetate (CTA), an extractant, di-(2-ethylhexyl) phosphoric acid (D2EHPA), and a plasticizer, 2-nitrophenyl octyl ether (NPOE), to allow the transport and preconcentration of free Zn species from the sampling medium to the receiving phase (0.01 mol L⁻¹ HNO₃ solution). Calibration was conducted by measuring the initial permeability under controlled laboratory conditions and by performing in situ kinetics at two different sampling points in the river. Sampling rates (R_s) of the PIM-passive sampler were also calculated, yielding results ranging from 1.7 × 10⁻¹⁰ to 3.0 × 10⁻¹⁰ m³ s⁻¹ for laboratory experiments and R_s values of 1.6 × 10⁻¹⁰ and 1.8 × 10⁻⁹ m³ s⁻¹ for in situ studies. The in situ calculated P₀ (initial permeability) was used as the calibration approach to determine the TWA concentrations of Zn in the Osor River in subsequent sampling campaigns, and values between 2 × 10⁻⁷ and 1.59 × 10⁻⁵ mol L⁻¹ of Zn were obtained. The PIM-passive sampler was then used to screen for Zn pollution in several other rivers without any evidence of pollution by this metal being found.