Elsevier

Environmental Pollution

Volume 193, October 2014, Pages 233-239
Environmental Pollution

Development of a passive sampler for Zinc(II) in urban pond waters using a polymer inclusion membrane

https://doi.org/10.1016/j.envpol.2014.06.040Get rights and content

Highlights

  • A polymer inclusion membrane (PIM)-based passive sampler is proposed.

  • The time-weighted average concentration of Zn(II) in urban waters is measured.

  • The PIM contained di-2-(ethylhexyl) phosphoric acid (D2EHPA) as the extractant.

  • The sampler was calibrated under laboratory conditions in deionized and pond water.

  • A field application in urban waters was conducted successfully.

Abstract

The use of a polymer inclusion membrane (PIM) in a novel passive sampler to measure the time-weighted average concentration of Zn(II) in urban waters is described. The passive sampler consists of a compartment containing an acidic receiving solution, which is separated from the external source solution by a PIM consisting of 40 wt% di-2-(ethylhexyl) phosphoric acid as the extractant, and 60 wt% poly-(vinyl chloride) as the base polymer. Two laboratory passive sampling techniques were tested. One involved immersion of the passive sampler into a source solution (“dip-in” approach) for a predetermined period of time while in the other one the source solution was flown past the membrane of the sampler (“flow-through” approach). The latter approach was found to be more suitable for the calibration of the passive sampler under laboratory conditions. A successful application using the “dip-in” sampling approach in urban waters has been conducted for proof of concept.

Introduction

Elevated zinc concentrations are frequently encountered in urban aquatic environments (Makepeace et al., 1995, Pettigrove and Hoffmann, 2003), especially those receiving industrial runoff (Gale et al., 2006, Sprovieri et al., 2007) and roads (Callender and Rice, 2000). Although Zn(II) is an essential trace element in plants and animals, as it is involved in protein synthesis and metabolism, long-term excessive exposure to it may result in oxidative stress, thus affecting the growth and development of organisms. It has also been found that long-term exposure to Zn(II) can have sub lethal effects on the populations and physiology of fish (Giardina et al., 2009). Therefore, its constant monitoring in natural waters is important in order to detect point sources of Zn(II) pollution and minimize or eliminate their emissions. Passive sampling is a sampling approach that allows the determination of the time-weighted average concentration of pollutants over extended periods of time (e.g. a few hours, or even up to a few weeks). Thus, unlike spot (grab) sampling, episodic pollution events can be easily detected (Namieśnik et al., 2005, Vrana et al., 2005).

Passive samplers are usually composed of a semi-permeable barrier, which separates the source phase, i.e. the external aquatic environment, from the receiving phase, where the analyte is collected (Vrana et al., 2005). The barrier can be selected according to the species being sampled and it also determines how fast a single or multiple species are collected in the receiving phase. Existing passive samplers for metal ions utilize mainly hydrophilic porous membranes or supported liquid membranes, prepared by impregnating the pores of a microporous hydrophobic membrane with a suitable organic extracting solution. Examples of hydrophilic porous membrane devices include the diffusion gradient in thin-films (DGT) device and the Chemcatcher® (Allan et al., 2007, Allan et al., 2008). Examples of liquid membrane devices include various semi-permeable membrane devices (SPMDs) (Prest et al., 1995), the stabilized liquid membrane device (SLMD) (Brumbaugh et al., 2002), and the permeation liquid membrane (PLM) (Slaveykova et al., 2004) sampler.

There are certain disadvantages associated with the passive sampler types mentioned above. In a hydrophilic porous membrane device such as DGT, the inclusion of a time-consuming pretreatment step involving elution of the analyte from the solid sorbent phase using organic solvents and/or acids is the main drawback. Some passive samplers employing supported liquid membranes can overcome this disadvantage in cases when the receiving phase (e.g. an aqueous phase) can be directly analysed. High analyte preconcentration can be achieved in the receiving phase due to the driving force created by a counterion gradient across the membrane. However, the main drawback of supported liquid membranes is their relatively short lifetime due to leaching of the organic extracting solution into the adjacent aqueous phases which results in limited sampler's durability (Chimuka et al., 2004).

In the present paper, a novel passive sampler for measuring the time-weighted average concentration of Zn(II) is proposed which consists of a polymer inclusion membrane (PIM) as the selective semi-permeable barrier along with an acidic aqueous solution as the receiving phase. The polymer-based liquid membrane concept has been known for over 40 years (Nghiem et al., 2006, Almeida et al., 2012). It has been proposed as a possible alternative to conventional solvent extraction and it has also been used in chemical sensing in ion-selective electrodes (Almeida et al., 2012). Only recently such polymer-based liquid membranes have been termed PIMs. Their stability has been proven to be better than that of supported liquid membranes (Nghiem et al., 2006, Almeida et al., 2012), already used in passive sampling. Moreover, these membranes have been shown to have great potential for the selective separation and recovery of target chemical species which has led to exciting analytical (e.g. online separation and preconcentration in flow analysis (Zhang et al., 2012, Zhang et al., 2011, Nagul et al., 2013) and development of paper-based microfluidic devices (Jayawardane et al., 2013)) and industrial (O'Rourke et al., 2009) applications. To the best of our knowledge, their application to passive sampling has not yet been reported.

Polymer inclusion membranes (PIMs) are a type of liquid membranes, where a suitable carrier or ion-exchanger is immobilized within the chains of a plasticized thermoplastic polymer often referred to as base polymer. The carrier is essentially a complexing or ion-exchange reagent, responsible for binding the species of interest (i.e. analyte) at the membrane/source phase interface and transporting it across the PIM. The analyte is back-extracted into the receiving aqueous solution by a suitable stripping reagent thus releasing the carrier that diffuses back to the membrane/source phase interface where it can bind another analyte ion/molecule. The transport of the analyte across the membrane continues even when the total analyte concentration in the receiving phase becomes higher than that in the source phase. This transport process is known as facilitated transport (Nghiem et al., 2006) and it is illustrated in Fig. 1 which presents schematically the transport of Zn(II) across a membrane containing an acidic diprotic carrier (H2L) and a strong mineral acid as the stripping reagent.

The analyte concentration in the receiving phase of the passive sampler can be measured by a suitable analytical method either directly or after derivatization. Due to the facilitated membrane transport outlined above PIM-based passive samplers are expected to provide a high level of preconcentration of the analyte in the receiving phase, thus allowing the use of less sensitive analytical methods. In the present application, a PIM-based passive sampler is proposed using di(2-ethylhexyl) phosphoric acid (D2EHPA) as the carrier. D2EHPA is a common, commercially available acidic extractant proven to have good selectivity for Zn(II), even in the presence of other common metal ions (Kolev et al., 2009). In addition to developing a Zn(II) passive sampler, the research reported in the present paper provides a proof of concept regarding the applicability of PIMs in passive sampling.

Section snippets

Reagents and solutions

p-Tosyl-8-aminoquinoline (p-taq), used for the fluorimetric determination of Zn(II), was synthesised as described by Billman and Chernin 1962. Stock solutions of p-taq were made up in ethanol, and warmed to 50 °C to ensure complete dissolution when preparing working solutions. Two different working reagents of p-taq were prepared according to the pH of the samples to be analysed. Thus, in the case of neutral samples the reagent was prepared by mixing 100 mL of the stock p-taq solution with

PIM extraction and transport of Zn(II)

D2EHPA is a commercial acidic extractant, and a PIM containing this carrier was found to extract Zn(II) (Kolev et al., 2009) in the same way (Eq. (1)) as the corresponding liquid–liquid extraction system (Rydberg et al., 1992).Zn2+(aq)+3/2(HR)2(mem)ZnR2·HR(mem)+2H+(aq)where (HR)2 refers to the dimeric form of D2EHPA and subscripts (aq) and (mem) refer to the aqueous and membrane phases, respectively.

The facilitated transport of Zn(II) across the membrane in the case of a strong mineral acid

Conclusions

A novel passive sampler has been developed for monitoring the time-average concentration of Zn(II) in stagnant pond waters. In this sampler, a PVC-based PIM, containing 40% D2EHPA as the carrier has been used as a selective for Zn(II) semi-permeable barrier separating the aquatic system from the 0.1 mol L−1 HNO3 receiving solution. This application of a PIM represents a further example of the potential of these membranes in analytical separation. The passive sampler has the advantage that the

Acknowledgement

The authors would like to acknowledge Dr David Sharley and Mr. Daniel MacMahon from CAPIM (Centre for Aquatic Pollution Identification and Management) for assistance with the field application of the passive samplers.

References (30)

  • M. Sprovieri et al.

    Heavy metals, polycyclic aromatic hydrocarbons and polychlorinated biphenyls in surface sediments of the Naples harbour (southern Italy)

    Chemosphere

    (2007)
  • L.J.L. Zhang et al.

    The use of a polymer inclusion membrane in flow injection analysis for the on-line separation and determination of zinc

    Talanta

    (2011)
  • L.J.L. Zhang et al.

    On-line extractive separation in flow injection analysis based on polymer inclusion membranes: a study on membrane stability and approaches for improving membrane permeability

    Talanta

    (2012)
  • I. Allan et al.

    Evaluation of the Chemcatcher and DGT passive samplers for monitoring metals with highly fluctuating water concentrations

    J. Environ. Monit.

    (2007)
  • I. Allan et al.

    Chemcatcher (R) and DGT passive sampling devices for regulatory monitoring of trace metals in surface water

    J. Environ. Monit.

    (2008)
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