An environmentally-benign flow-batch system for headspace single-drop microextraction and on-drop conductometric detecting ammonium

This work presents a lab-made automatic flow-batch system for headspace single-drop microextraction and on-drop conductometric sensing ammonium. Sample and NaOH solution are simultaneously pumped into a reaction chamber (RC), where ammonium is converted to ammonia by raising pH. The converted ammonia then diffuses into the headspace of the RC, and reacts with a 100 mM boric acid drop. The conductivity of the drop is measured by an on-drop conductivity probe, which is made by two stainless-steel contacting electrodes. The result shows that the increasing rate of conductivity has a linear relationship to the ammonium concentration in sample (R2 = 0.9945). This method has a linear range up to 400 μM, a limit of detection 2.8 μM, a relative standard deviation of 3.0% (200 μM, n = 10) and carryover coefficient 0.028. Measurements of river waters, lake waters and wastewaters have been demonstrated. The recoveries have achieved from 99.0 to 114%. This method avoids using of harmful or odorous reagents and follows the concept of green chemistry. [Display omitted] •An environmentally-benign and automated flow-batch system for detecting ammonium without using harmful or odorous reagents.•Using liquid drop as a renewable adsorbing interface avoids issues of clogging and biofouling in membrane-diffusion units.•Headspace microextraction and on-drop detection simplify the procedures and increase the sample throughput.