Miniaturized flow-injection-analysis (μFIA) system with on-line chemiluminescence detection based on the luminol-hypochlorite reaction for the determination of ammonium in river water

摘要

A miniaturized flow-injection-analysis system constructed from glass and polydimethylsiloxane was employed for the determination of ammonium in river water. The sample was filtered and delivered to the reactor chip electro-osmotically using a disposable fritted capillary, while reagents were delivered to the system by gravity. Ammonia was mixed with the hypochlorite, to form a monochloramine. Once the alkaline luminol (3-aminophthalhydrazide) was delivered to the system, it was oxidized by the unconsumed hypochlorite emitting a bright blue light (λ-(max)～440nm) that was detected using a miniaturized photomultiplier tube (PMT) located directly under the chip. The calibration model for ammonium standards was linear up to 0.1 μgmL~(-1) (y = - 8.96.x+ 1.02; correlation coefficient, r~2 = 0.9715) over a working range of 0.0-0.5ugmL~(-1). A detection limit of 10±6ugmL~(-1) was achieved with a precision value of (RSD ≤ 6.4%), for n = 5. A direct and standard addition method were used to determine the concentration of ammonium in a river-water sample (from the Humber Estuary, UK) which was found to be 0.075±0.005μgmL~(-1) with a precision value of (RSD ≤3.7%), for n = 9. The results obtained showed good agreement with the average concentration 0.065 μg mL~(-1) (provided by the local environmental agency), for the analysis of ammonia at different sample points on the estuary.