Development and application of a portable fluorescence detector for shipboard analysis of ammonium in estuarine and coastal waters

Abstract

Herein, a novel homemade portable fluorescence detector that is simple, smaller, and transportable for the shipboard analysis of ammonium in estuarine and coastal waters has been developed and applied in a flow system for ammonium analysis based on the reaction of ammonium, OPA, and sulfite. The detector incorporates a UV-LED, two band pass filters, a photomultiplier tube (PMT), a modified flow cell, and an electronic circuit with a constant voltage supply and a constant current supply. The modified flow cell of the detector used in this study can avoid the interference of air bubbles in the fluorescence signal. A 100 nmol L⁻¹ ammonium standard solution was continuously measured for 90 min. An RSD of 0.8% (n = 38) was obtained, indicating the good stability of the detector. Compared with the commercial PMT-FL fluorescence detector, the homemade detector was smaller and lightweight and demonstrated better sensitivity (approximately 11.4% higher). Moreover, the parameters of the flow system were optimized. Under optimal conditions, a detection limit of 2.1 nmol L⁻¹ within the working range of 0–300 nmol L⁻¹ was obtained. Using the underway sampling system, the homemade portable fluorescence detector was applied in Jiulongjiang estuary, and the distribution of ammonium in the surface seawater was obtained.