Calibration of a passive, in situ, integrative sampler for monitoring of microbial biotoxins in aquatic environments

In this work, an integrative passive sampler based on a silicone membrane filled with a suspension of γ-Fe₂O₃ at pH 3.5 was developed. The novel device was calibrated for the measurement of microcystin concentrations in water. Laboratory calibration studies of the passive sampling devises under controlled conditions of temperature, water turbulence, and analyte concentration were conducted in order to establish how variable environmental conditions affect the novel sampler's performance. The chemical uptake of microcystin (MC)-RR, -LR, and -YR into the passive sampler remained linear and integrative throughout the 28-day exposure. The relative standard deviations of mean concentrations obtained using silicone-based sampler ranged from 1.42 to 3.74% for microcystin-LR, -RR, and -YR. The values for reproducibility from triplicate samplers ranged from 3.5 to 7.1% for microcystin-LR, -RR, and -YR. The detection limits on high performance liquid chromatography (HPLC) with PDA detection for microcystins LR, RR, and YR were 24.7, 17.2, and 23.8 μg L⁻¹ respectively, calculated as three times the signal to noise ratio. The rate of accumulation of most of the MC compounds tested was dependent on temperature and flow velocity. Furthermore, the sample matrix, e.g. humic substances, had no significant effect on the concentration of compounds trapped in the acceptor solution and once these MC compounds were trapped in the acceptor phase they did not diffuse back during the deployment period.