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

Abstract

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 ∼ 440 nm) 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 µg mL−1 (y = −8.96x + 1.02; correlation coefficient, r 2 = 0.9715) over a working range of 0.0–0.5 µg mL−1. A detection limit of 10 ± 6 µg mL−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 ± 0.005 µg mL−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.