Development of a passive sampler based on a polymer inclusion membrane for total ammonia monitoring in freshwaters

A passive sampler for determining the time-weighted average total ammonia (i.e. molecular ammonia and the ammonium cation) concentration ( C TWA ) in freshwaters, which incorporated a polymer inclusion membrane (PIM) as a semi-permeable barrier separating the aqueous source solution from the receiving solution (i.e. 0.8 mol L −1 HCl), was developed for the first time. The PIM was composed of dinonylnaphthalene sulfonic acid (DNNS) as a carrier, poly (vinyl chloride) (PVC) as a base polymer and 1-tetradecanol as a modifier. Its optimal composition was found to be 35 wt% commercial DNNS, 55 wt% PVC and 10 wt% 1-tetradecanol. The effect of environmental variables such as the water matrix, pH and temperature were also studied using synthetic freshwaters. The passive sampler was calibrated under laboratory conditions using synthetic freshwaters and exhibited a linear response within the concentration range 0.59–2.8 mg L −1 NH 4 + (0.46–2.1 mg N L −1 ) at 20 °C. The performance of the sampler was further investigated under field conditions over 7 days. A strong correlation between spot sampling and passive sampling was achieved, thus providing a proof-of-concept for the passive sampler for reliably measuring the C TWA of total ammonia in freshwaters, which can be used as an indicator in tracking sources of faecal contamination in stormwater drains. Graphical Abstract Cross section of a passive sampler (amplified membrane thickness) with a schematic representation of the transport mechanism for total ammonia across the dinonylnaphthalene sulfonic acid (DNNS)-based polymer inclusion membrane (PIM). Black solid arrows illustrate the extraction process. Grey solid arrows illustrate the back-extraction process