Technical development and optimisation of a passive sampler based on polymer inclusion membrane for uptake of copper, nickel, cobalt and cadmium in surface waters

The shortcomings of conventional sampling methods as grab sampling has led to the development of alternative approaches especially those based on passive samplers. The challenge of passive sampler’s despite being cheap to use and being integrative in nature is that there are limited commercial suppliers especially for those on water related applications. Further, technical development is still ongoing on the types of design and resin materials. In this work, the technical development, optimisation and preliminary application of a passive sampler based on polymer inclusion membrane is reported. The passive sampler consisted of a chamber made of polytetrafluoroethylene that has a lumen receiver volume of 5.5 mL solution. A membrane synthesised with polyvinyl chloride in the presence of di-(2-ethylhexyl) phosphoric acid as carrier was then placed as a barrier between the receiver and source phases. A screw cap was used to hold the membrane and the chamber together. The passive sampler based on polymer inclusion membrane was characterised using various techniques for stability, morphology and functional groups. The optimum parameters under which the passive sampler worked were as follows; 40% w/w di-(2-ethylhexyl) phosphoric acid impregnated in membrane pores, source solution pH set at pH 6, 1 mol L−1 HNO3 as receiver solution, membrane thickness of 100μm and with deployment time up to 12 days. The passive sampler based on polymer inclusion membrane was found to have large time lag up to five days and then linear uptake observed up to 12 days. The stripping phase into the receiving phase was limiting rate in the transport of the metals across the membrane. Preliminary test of the developed passive sampler in the field proved that it could be used for extraction of the target metals. The order of extraction of the target metals was Cd >> Cu >> Co > Ni. However, other metals were also extracted from the water especially Fe, Zn, Mn, Mg, Na and K. The designed passive sampler holder was found to be very versatile and rugged and is the first reported holder made entirely of polytetrafluoroethylene.